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Stri6lt ar per the now nvised syllabus ot 'G' scheme w'e l acalhmic Fir 2014'201 5

lndustrial
= Fluid Power Third Year DiPloma - sem€ster vI
tlGchrnlcal Engine€ring / Production Engine€ring /
Production Y€Ghnology Enginecring Group

P. K. Ghandrashekara R. B. Mali
xoEto9^ Priccl225/'
@
h-Max"-.,"*.-
lnnovation Throushotr
Prrl]'acchnic lrivinnrn I I ltilll illllllllillililillll[
 Preface
Lel us compare lwo p6rsons, one is a WWF champion and the other is
a school boy o, your school, Whal is th6 diJloronco belweon th6m?
School boy is clever and quicker. He can run last, he can do the things
lasler. Whereas, the WWF champion has lol of power, he can liti heavy load
and he can do alllhings which requiG lol of rorc6 and power.
BLrl, bolh have same pans in lheir body. Parts of stronger man are
stronger and lhose ol small boy a€ nol lhal much. Functioning ol lhose parts
are oxaclly similar, Ey6s, hean, hands,l€gs elc. ars nol diflerent lor them,
We can correlale WWF champion lo hydraulic syslem afld school boy
lo pneumalic system. Hydraulic systems produce huge amounl ol torce, they
can do very heavy iobs. Pneumatic syslems produce comparatively small
lorce, bul they are very lasl in operalion.
Bul, parts oJ hydlaulic syslem and pneumalic system are nol diflerenl
lorm sach othsr. They ar€ one and lhe same. Hydraulic compononls (such as
valves, acluators elc.) are stronger, bigger and heavy. Pneumatic paris are
lighler in weighl, made of light materials. Construclion and lunclioning are

Once we sludy one system, maior pan of siudy ol the olher system is
over. There is no need 10 study lie same lhing lwice under two dillerenl
headings.
ln this way, the syllabus of'lndusldal Fluid Power o, sixth semesier
diploma in mechanical enganeering is very simple and compacl. whalever we
l€am in lirst thrse chaplBrs is snough lo know the rssl o, the things.
We honestly lried to cover eveMhing related lo the syllabus in this
book and to arrange them in lhe most etlicient manfler lor easy reading ol the
book. While doing so, the supporl and cooperation shown by the publishing
leam is extremely admirable.
We are grateful lo ihe leam ol Tech-Tax publicaiions tor thek limely
help and provision of necessary resources. We are thanHul to
Shrl. Sachin S, Shah .nd Shri. Pradlp Lunawat for providing us an
opporlunity lo bring this book in its excellent lom lo hands of our needlul
students.
SLrggeslions and commenls from leachers, prolessionals and students
are mosl welcome for improvemenl otlhis book towards excellence.
P. K. Chandra3hekaaa
R. B. Mali

trtro
(e)
 Syllabus

Name of th€ topic Hrs Marks

l. Basics of oil hydraulic aysterDs

Specific Objectiv6 :
. Idefltify vanous compon€nts in simple oil hydraulic

. List the types of various components in simple oil

hydraulic circuits.
. Explain the construction and working principle of
various components in simpl€ oil hydraulic circuits.
Contents l8 24

. General layout, Applications, Merits and linitations

of oil hydraulic syst€ms.
. Overview of essential prop€rties of oils used in oil
hydraulic cncuirs.
. Construction, working principle, applications and
symbols of Vane pump, gear pump, Gerotor pump,
screw pumP, piston pumP.
(Reler Chapler 1 )

2. Hydraulic valvcs, actuators arld acc€ssori€s

24 Marks

. Select valves, actuato{s and accessories for the given

application of hydraulic circuit.

l8 24
Construction, principle of working and symbols of
-
hessurc control valves pressur€ relief valve
dircct, pilot operated , pressure rcducing, prcssure
unloading. S€quence vahe\. counLerbalanciDg.

- Poppet valye, spool

Direction control valves
\alve, 212, 3D, 42, 5/3, rnethods of actuation.
(10)
 Nrme of lhe lopic Hnj NIarks

Typcs of differEd centcr Frositions. check valves,

pilot operaled ch€ck valves
F'low control valves -
pressure comp€nsated, non
pressure comPensated flow control vdve,

Clasifi cation of actualors

ConstrucrioD, \iorkbg principle and symbols of
Rorary Actuators - Hydmulic motors
Linear Actuarors Cylhders - single actitrg,
double acting, atrd lheir subtypes. Differenl
mouotio8 methods.
Acccssorics
Construction, working principle and symbols of
PiFs. Hoses, Fittings. Oil filters, Serls snd gaskets,

(Fsllr Ch.Pror 2)
3. Oil hydrrulic Cirqlits 15 Drlls
spocihc Obj.c{v6 :
. Draw layout of oil hydraulic circuils.
. Explain workinc ofoil hy&aulic circuits.
. Develop oil hydmulic circuit for diffcrent
applications.

Contents :
I t2
'Metcr in' ,'Meter out', 'Bleed off. Unloading , t{o
cylinder syncbronizinS, regeD€radve,
counre.balance , dual pumP unloadinS circuils.
Sequencing circuit - time dcpeodent and pressure
dependeot.
Oil hydraulic circuils for milling machine, shaper
machine.
(Rel€r ChaPter 3)

(11)
 Name of tte toplc Hrs Marks
4. lntroduction to Ind corDpoDcnts ol pneuEdic
syst ms 12 mar}l
Speclfic ObjcctiY€s :
. Identify various components in simple pneumatic

. List lhe typ€s of various components io simple

pneumatic circuits.
. Explain th€ coostruction and working principle of
various comfroneots in simplc pneumatic circuits.
CoDLtris :
. Applicationsofpneumaticsysicms
. Cen€ral layour, merirs and limirations of pneumaric
. S€l€ction of air compressors for pneumatic circuits
l.t 24
. Constsuction, pdnciple of working and symbols
of
. Pr€ssurE rEgulating valves, DirEctioo control
valves, Flow contml valves

. ConsEuction, working ahd symbols of

. Rotary Acirators - Pneumatic motors
. Lilear Actuators - Cylinders - singl€ acring,
double acting.

. Constsuction, wo*iog and symbols of Pipes,

Hos€s, filtings, FRL unit.
(R6ler Chapter 4)
5. heumstic Ciftuits 12 mr*s
Sp.ctnc Obj€ctiYd :
. Draw layout of simple poeumalic circuirs.
Cooteots :
0lt l6
. Sp€ed control circuits for doubl€ acting cylinder and
bidirectional air motor
. Sequencrng circuits -
Position based sequencing
circuil and time dela 5)
Tolal 6l l(x)
JJJ
\12)
81,," 1 Tabie ol Conlenis

Chapler 1 : Basics ol Oil Hyd6ullc Syslems 1-1 to l{6

1.1 Fluid Power System ...1-2

I .I L Advantages of Fluid Po*er Systems ...t-2

L | .2 Applications of Fluid Power Systems I,j
I L3. DifferEnce b€twccn Hydmulic Sysl€m and
Pneumadc System .........1-,

L I -4 Differeoce b€tween Hydraulic Moto(

Air Motor ard El€.tn€ Motor l-5

1.2.1(A) General layout of Hydraulic System t-7

1.2.1(B) Compone s of Hydraulic Systcm ...................... ....l-8

t.2.2 Applications of Hydraulic Systems l- 10

1.2.3 Advantages of Hydraulic Systems l -11

1.2.4 Limitatiotrs of Hydtaulic SYstems t-t2

I .3 Properties of Hydlaulic Oil l-13

1.3.1 Mass De.sity .......1-13

1.3.2 WeiSht Density l-13

1.3.3 Sp€.ific Gravity l -13

1.3.4 ComprEssibility l-14

1.3.5.2 Kioematic Viscosity .........1-15

1.3.5.3 Gradas of Hydraulic Oil ..............................'. " 1'16

1.3.6 Viscosity Index (Vl) t-t6

1.3.6.1 Proc€durE to Dcterminc VI of Given Oil -.. " 1-17

1.3.? NeuEaliz.ationNumb€r t-18

I.3.t Flash Poi1l .....- " l-lt

 EP (MSBTE 2

1.3.10 Oxi&tioo Srabiliry ..,....'....,'...,,....'....,....,1-18

1.3.1I Lubricity _.1, t8
t..l Required Properties of Hydraulic Oil
Selection of Oil (Requned Prop€rties of Oit) t-19
1.5 Pump......-. l-20
1.5.1 ClassificarionofPumps t-20
1.5.2 Positive Displacement Pump (PDP) t-2t
1.5.3 Non Positive Displacemenr pulnp (NpDp) ..__..............1-21
l-5.4 WorkinS principle ofPDP and NpDp t2t
I .5-5 Reasons for not using rcciprocariog
pump in hydraulic sysrems ... ..._................................1-72
1.5.6 Reasons for Prcferriry Rotary Pumps in
Hydraulic SysLms (Advantagcs of Rotary pDp) ......... l-23
1.5.7 Compariscn berwe€n PDP and NpDp t-u
L6 Classification of Rorary Pumps t-25
1.6.1 Extemd ct3r Pump t-25
I.6.2 Intemal cear Pump 1-26
1.6.3 Lobe Pump t-27
L6.4 Ci€-rolor (Genemted Rotor) hmp t-28
1.6.5 Screw Pump ........ t-29
1.6.6 Advaniages ofGe3r Pumps t-29
1.6.7 Unbalanced Vane Po.p .-..-...-... l-30
1.6.8 Variable Displacement Vane pump l-31
1.6.9 Balanced Vane Pump t-32
1.6.10 SEaight Axis Piston Pump l-33
1.6-l I B€nt Axis Pislon Pump t-3/
1.6- l2 Stationary Cylinder Radial piston pump t -35
@]u,r, (*."-.) 3 Table ol Conlonls

1.6.13 Rotating Cylinder Radial PistoD ltmp .. .....1-36

1.6.14 Sel€ction Criteria for Hydraulic Pumps - .....1-17

1.6.15 ConFrison bet're€n G€.r PumPs. Vane

Pump and Piston Pump ....1,37

1.6.16 Trouble Shoo.ing of Hydr"aulic Systcms ..... ...-.......... ...1'3,

l;7 Imponant E'ramination Questions and Answers t,43

Chapter 2 : Hydraulic Valves, Actuators & acceas 2'-l lo 2-102

2.t ConEol Valvcs ................ ............. .......2'2

2.1.1 Classificatiotr of CooEoI va1vcs ............. .... ....................2-3

2.1.2 Factors to bc ConsiderEd Whil€ Sclccti.S

Connol valves - -..--........24
2.1.3 Pressure Control Valv€s .2-5

2.1.3.1 PrEssure Relief valve .2-6

2.1.3.2 Importance of Pressure Relief valve .2-7

2.1.3.3 Pressure Reducing valvc .2-a

2. 1 3.4 Comparison between Relief Valve and

Reduchg Valve

2-1.3.5 Uoloading Valve .2,1I

2. L3.6 Comparison b€twecn Relief Valve ard

UnloadioB Vslve ..-..... .... ....2'12

2.1.1.7 Counler brlance lnlve .....2-14

2.1.3.8 Scqucrce Valve .....2-t5

2.1.3.9 PressurE Switch ........ .......2'16

2.1.3.10 Hydraulic Fuse ................2-16

2.1.4 Dir€ctiooContsolvalves.................-.-...................2'17
2.1.4.1 Check Valve 2 l8

2.1.4.2 2nDtre,rnol.Conhl Valve ........ ... .......-..... ..... ...-" 2-19

2. 1 .4.3 3/2 Direction Conlrol valve ... .... .. .2-21
Lfi rrp Tabl6 ol Contents

2.1.4.4 4nDirtlnonCo$uolValve.........................................2-23
2.1.4.5 #3 Dircction ConEol Valve
2.1.4.6 512 DirEcrion Conrol Valvc 2-2a
2.1.4.7 Methods ofActuatioo ofDCV 2-30
2.1.5 Flow CoDEol Valves .................................. ...................2-3t
2.1.5.1 Fixcd ResEicrion FCV .. .2-31
2.1.5.2 Variable Restdction FCV .2-32
2.1.5.3 FCV with Rev€rs€ Fr€€ Flow .2-33
2.1.5.4 Pressure alld Temp€rature Comp€nsated FCy ...._...__...2-y
2.1.5.5 Cam Op€rated l.IV with Inregral
Check Valv€ (De&leration Vdvc) 2-35

2.1.6.1 Time Delay Valve 2-31

2.1.6.3 Twin Pressure Valve .2-39

2.1.6.4 Pilor Opetar.d Ch€.k Valve .24t)
2.1.6.5 3/2 PopFt TyF Dir! tion Contsol Valve 243
2.2 Actualors io Hydraulic Systcm ................................ ....................245

2.2.1 ClassificaaionofAcruarors 245

2.2.2 Limar Actuaton (Cylind€N) 24
2.2.2.1 RotatingCylinders 247
2.2.2.2 Non-Rotatiry Cylind.rs .248
2.2.2.3 Other Types of Cylind€rs .2-56
2.2.2.4 CylinderMourtirss .2-A
2.2.3 Rotary Actuarors .2-62
2.2.3.1 Limited Rorarion Actuators ....-.................. ........_..........242

2.2.3.2 Continuous Rotation Actualors (Rotary Motom) .........2-&

E]o,., (r."r.) 5 Table ol Conienls

2.2.3-3 Comparison between Hvdraulic Pump and

.2-',72
Hydraulic Motor

2.3 Pipe Makrials fot Hydraulic Sysl.ms .-...... ""- " '2'-13

2.3.1 nexiblc Hos. .......................2-73

2.3.2 R€quircments ofFluid Po*er Plumbing

2.3.3 Requirerne of Hoses and Hos€ Fittings _.................2-7 6
. _

2.3.4 Pipe Size Specification . - - "-" - '2:77

2.3-5 various l,ocsas in PiFs . *----- - " " 2'78
2.3.6 PiPe Fittings and Tube Fittings -'-,-'-" 2'79

2.4 Seats in Hydraulic Sy$.m " - 2-80

2.4.1 Classification of seals . ... " " " " 2_80

2.4.2 Futrctioos ofsal " 2-81

.2-82
2.4.3 Causes for Failure of Seals

... .2-83
2.5 Filter in Hydraulic Syst€m
.2-83
2.5.1 ClassificationFillel!
2.5.2 Surfa.e TW€ Filtcr " 2'U
2.5-l Edge TrF Filter

2.5.4 Deplh TWe Filter

2-85
2-5.5 By- Pass TYPe Filter
2.5.6 FulFlowFilt{ " '2-86

2.5.7 Proportioml Frlter "" " - 2-86

2-8',7
2.5.8 FiltrationMethods
.2-89
2.6 Hydraulic Rcservoirs

2.7 HydrNlicAccumulator-""2_91
2.7.1 classification of Accumulators "" " " 2'c2

2.7.2 Ac,;usulaaot Circui! ..... --'-_--"-'--' " - 2-91

2.A htensifrers or Pressure Boosters " " ,' " 2-95

 Eff,r" 1r""r.) 6 Table of Conienls

2.8.1 Singl€ Acting Boosrer ............ ................ ..._.........2-96

2.8.2 Double Actins Booster .. .........2-96
2-9 lrnponant Examination euesrions and Answers ._..... ._........._....2-98

Chaptor 3 : Oll Hydrau c Circutts 3_1 to 3_S9

3.1 Op€rating SAC using l/2 DCV .3-2
3-2 Operating Uni-dirEctional Motor using 32 DCV 33
3.3 Operaring DAC using 4/2 DCV
3-4
3.4 Operating Tuo SAC using One 4/2 DCV
.3-5
3.5 Operaring Only One SAC using a 4/2 DCV ............................._...3_6
3.6 OFrating DAC usinS 4/3 DCV .. .............. ........ .. ......................3_7
3.1 Op€rathg Bi-diredional Moror using.t/3 DCV
3,9
3.8 Two Hand Opera.ion Circuit -.._-.-..._.._-...._.......... ................3-10
3.8. I Two Hand Op€ration of SAC Usitrg Two 3/2 Valv€s....3,10
3.8.2 Two Hand Op€rarion ofSAC Using
Twir pressure VaIve ........_._--_...--._..........._...........3_ll

3.8.1 Tiyo Hand Op€ration of DAC Using Two 3/2 Valves .3_12
3.9 Operaring DAC using 5/2 DCV .............................. ........._........._3-13

3.10 Auromaric Conrinuous Op€rarion of DAC

l-14
3.lO.l By using Limit Swirches atrd Double
Solenoid 4/2 DCV ............._l_14
3.10.2 By using Limir Valvcs atrd Doubte pilor ztl2 DCV ......3_15
3.l l SFld Control Circuirs .......................3_17
3.ll.t MeGr-inCircuirforDAC.............................................3-17
3.1 1.2 Meler-out Circuit for ExteDsion of DAC ......................3-19
3.11.3 Bl€ed-off Circuit for DAC 3-20
3.II.4 Types oft ad on Hydrautic Cylhder
@,r" (u"ur.) Table ol Contents

3.11.5 Applications of Merer-in, Meter-out & Bleed-off

Circuits
3.11.6 Adva ages and Limitations of Mcter-oul
Meter-in and Bleld-off Circui6
" " 3-23
3.t2 Scqucming circuits using s€quencc valves " " -,' -,' 3-25
3.12.1 Circuit to OFmL Two SAC in Seque,ce " " 3-25
3.12.2 Cttuit to OPcrate Two DAC in
scqucnc. in Orc Dtrection oDly - 3-26

3.12.3 CirEuit ro OFrate Two DAC itr

Sequcnce in Both Dir€ctions ...... --" " 3'27

.......3-D
3.13 S.quencing Citcuils usiDg Limit valves

3.14 Sequeocing Circuits using Limit switches " " "" 3-3I

3.15 Sy.cfuooizing Circuit -"" " 3_33

3.16 Hydraulic ShaPer Circuit .. . 1-A

3.11 Hydraulic Milling Machine or Hydraulic Surface

3-36
Grinding Machine -................

Circuit .. ........ .........3-38

3.18 Regenerative

3.19 Hydraulic Cncuit for Fast Approach. Slow

1-1t1
Curing and Fast R€lum of Machine Table

3.m Dual Pump Hydraulic Ctcuit .. .." -"""

3.21 Hydraulic Pr€ss Circuit usiog Unloading valve " --" " 3{6
.3 48
Hydraulic Circuil using Counter Balaffe Valve
3-,19
3.23 D€crleration Circuil or Cushioning Circuit

3.24 Application of Shude Val "-" " 3'50

3,5t
3.25 Apptication of Twin Pressure valve

3.26 Applicatiotr of "Pilot-tcoPeo Check va'lve" -- " " 3-52

........3-54
3.27 Hydraulic Time D€laY Valve Circuit
 E' IFP (MSBTE) 8 Tabie ol Contents

3.28 Power Saving" in Hydraulic Sysrems ........................................3-55

3-29 Imponan Examination euestions and Answ€rs .... __......._...........1_5j

Chapter 4: lntroduction to and Components ot

pneumatic Systems +.t to 4-07
4.1 Inrlducrion ........_.......... .._...................4-2
4.1.1 GeDeral liyout of pneumatic Sysrem 1-2
4.1.2 ComponenrsofpneumaticSystem.................................4-3
4.1.3 FacroN to be considered while Selecting rte
Componenb of pneumaric System .u
4.1.4 Advantages of pneumaric Systems
.4-5

4.3.1 Air Filter ................................+12

4.3.3 Air Lubricaror ...',,'.,,,...',,..,,..4.13

Condensation of Warer ..................................+15
4.4.1 Moisrure Sepamtor ........_........_.. .4-t5
4.4.2 Coatescence Element Type Filler .4-16
4.4.3 Air Dryers ..4 t7
4-4.3.1 RefiigeratedAirDryers......_............................._...........+tj
4.4.3.2 Chemical Air Dryers...... -,''...,,,.-.'4.18
.15
.... .. ... . .... ......+19
4.5.1 ClassificationofcontsolValves. ...........+20
EEl,r" (r."r.) 9 Table ot Contonts

4.5.2 Factors io be consideBd while sele'ting

conrrol valves " 4-21
4.5.3 Pressue Control va1ves .. .. ..."'--- " -" " 4-22
4.5.3.1 Pressure Relief Valv€ ... ......... - -" "4-23
4.5.3.2 Pressue Reducing Valve (Pressurc Re8plator) " --" 4-24

4.5.3.3 Sequence Valve -"" "'+25

4.5.3.4 Pressure Swit€h "" " " 4-26
4.5.4 Direction Control Valves ... .... . "---"-" - 4-21
Check valve
.,,..-,+28
4.5.4.1
2/2 Dircction ConEol Valve
......+29
4.5.4.2
3/2 Dir€ction Control Valve ... ...-..+31
4.5.4.3
...._.+33
4.5.4.4 4f2 Direction Control valve

4/3 Dircclion Conrol val ......4-35

4.5.4.5

5/2 Direction ConEol valve

.......+31
4.5.4.6
Melhods of actuation of DCV ... .......4-39
4.5.4.1

4.5.5 Row Control Valves -- -.- .-"'-" " " " 440
4.5.5.1 Fixed Restriction FCv .............. - +4O
4.5.5.2 variable Restdction FCv ..-.-..- -"_ ,' " 4_41

4.5.5.3 rcv with Reverse Free Flow ..."-_'.._-- - -- _ 442

4.5.5.4 Cam opeBted FCv with lntegral
Check Valve (Deceleration Valve) - .443
.445
4.5.6 SPecial tlTe valves
.445
4.5.6.1 Timedelayvalve .

.4.46
4.5.6.2 shuttl€ valve
4.5.6.3 Twin Pressure..."
Valve ' ..................447

4.5.6.4 Quick Exhaust Valve .-" ' ...... ........................,r-48

4.5.6.5 3/2 Poppet Tvpe Direction Control Valve " ' ..449

System .".." -"--"'- .. "" ".._ --'"' ..+50

.1.6 Aduators in Pneumatic
 @1,r" 1r""rr1 l0 Tabie ol Contenls

4.6.1 Classification of Actuators ........._....... __..__..+5t

4.6.2 Limar Actuarors (Cylinders) ........... .. . ..---..-4-52
4.6.2.1 Roradrg Cllinde
4.6.2 2 Non-roraring Cylinders .......... ,..',.',4 53
4.6.2.J OrherType.ofCytinder. ...... ........... .-......4 56
4.6..1 Rohry Acruatoa .....__4-&
4.6.1.1 Lim'redRorationActuators ... .......... ...__.__4_60

4.6.1.2 Continuous rohnon Actuators (Rolajy Motors) ... .....___4_62

1.7 Pipe Marerials for Pneumalrc \)slem\ ......... ..... .... ...... ......4-66
4-7-l Fler.ible Hose -....._4-67
4.7.2 Selecrion ofpipelines for pneumatic Syslem .......
4 7.1 Pressure RabnSs for pipe or Tube ......_4-69
4.7.4 Requirements of Ftuid power plumbins ............. ..__4-70
4.7.5 Requrrenlenr ofHoses and Hose Fillinr\ ............ __..4-70
4.7.0 P'peSizrSpec,fica[on .................... ................ ..._4-71
4.7 7 Pipe Fitun8s and Tube FininSs ..__4-71
4.8 Seals in Poeumatic System
-..4-74
4.8.1 Functions of Seals .__4-',74

4.8.2 Classificarion of Seats .............. ........ .._ .... .... ...4-75

4.8.3 Causes forFailure of Seals _.................................. ...1-76
4.8.4 VariousLossesinpipes ........................_...__.......... .__4-76
1.9 Filre n Pneumarjc Sy,lem
___4 77

4.9.1 ClassificationFilters ...4-7 7

4.9-2 SurfaceTypeFilter ..............._.........._.. ...4-',78

4.q.J Edge T}?e Fitrer ..4 78
4.9.4 Depth Type Fitte ._4-',79
4.9.5 By- Pass Type Filter ........_............-.... ._4-19
El,t" t MSBTE) 11 Table ol Conlenls

.4-80
4.9.6 Full Flow Filter
.4,80
4.9.7 ProPonional Filrc

4.10 Imponant Examination Quesrions and Answen "" " "" .4,81

: Clrcults 5'1to5'29
Chepiers Pneumatlc

5.1 Operating SAC using 3/2 DCV"" " " -" - -"" "5'2
5.2 Operating Uni-directional Motorbv 3/2
DCV " -"" '5-3
5.3 Operating DAC using 4/2 DCv "" - - -- -- '-- " 54
5.4 Operating Two SAC ushg One 4/2 DCV ' "
- " 5-5
5.5 Operating Only One SAC using a 42 DCV ---" "" " " 56
5.6 Operating DAC using 4/3 DCV " - - -"-" -" 5-7
5:l Operating BidirEctional Moror by 4/3 DCv - -"-" " 5-8
5.8 Dual Control (two Hand OPemtion) Circuit
- " " "5-9
5.8.1 Two Hand Opcration of SAC using Two 3/2 DCv " '5-9
5-8.2 Two Hand Operation of SAC using Twin
ftessue Valve " --" 5_10

5.8.3 Two Hand Operation of DAC using

..s-1t
Two ln Val\es
..5-12
5.9 Operating DAC using 5i2 DCV
DAC """ ..5-r3
5.10 Auromanc Continuous Operarion ot

5.10.1 By using Limit Switches and Double

5-13
Solenoid 4/2 DCV

using Limit Valves and Double Pilot 4/2

DCV ....5-14
5.10.2 By
....5-ls
5.ll Sps€d ContlotCrrcurt5
....5-15
5.11.1 Throttling-in Circuit for DAC
5.11.2 ThJonling_oul CIrcurt for DAC """"'"" " " " ....5-17

.....5 18
5.11.3 Bleed-offCircuil
EEl,." '12
Table ol Contents

5.t2 Sequcncing Circuirs using S€quence Vatves .........._........._...._...._5-20

5.13 SequencingCircuirr usingLimir Valves ...... ...... .... ..............5-21

5.13.1 Operate a SAC and a DAC in Sequence
.5-21
5.13.2 To OFrare Ttxo DAC in Sequence

5. t:t Sequencing Circuils using Limit Swilches

5.14.1 To Oprare a SAC and a DAC in Se4uenc€ ...._........._.5_23

5.t4.2 To OFra& Two DAC in Sequence.._......... _........._........5_24

5.15 Inpirlse Operated Pneumatic Circui( ..........................................5-24

5.16 Pneumariccircuilusingquiclexhaustvalve........._...................5-26

5.17 Tine delay valve circuit

-...,............................5-27
5.18 Imporran( Examinarioo euesrions atrd Answers
528
. Appctrdix A : ASTM D2270 Tabte........................,
AI toA-6
. Appctrdlx B : Fluid po*€r Slrrbok..-...,..........,,....8-t
ro B_9

D3D
Chapter

Basics of Oil
Hydraulic Systems

Syllabue :

. General layout, Appllcations, Merits and limitations of

oil hydraulic systems.
. ovetuiew of essential properties of oils used in oil
hydraulic circuits.
. Construction, working principle, applicatlons and
symbols of Vane pump, gear pump, Gerotor pump,
screw PumP, Piston PumP.
 lq EPt r 1-2 Easics ol Oit

'l .1
Fluid Power System

Fhrid Power system is a povrer transmission system in

which, tbe rransmissio[ ofpower ts-kes place by EeaDs of"oil
under presaure" or 'compressed air".
If "oilunder pressure" is used in the system for pow€r
tran8mission, then the system is called "Hyrlraulic system".
If "compressed air" is used in the system for power
transmission then t}le system is called -ptreumstic system".
When_large force alrd low speed is needed, hyalraulic system
should be selected.
Because, oil is incompressible. Its volu.me will not change
with increase in pressure. pressure can be increased to a;v
amount' nothiag bappeos to the voluEe ofoil.
More the pressure of oil, morc will be the force developed.
Hydraulic systems are slower in operation because, oil has
morc viscosity. Oil can not flow fast as compre6sed air.
When less force and higher speed is required, then
pneuDatic syst€m should b€ select€d.
A.s air is compressible itr nature, it catr not be pressurizd
to
large amount of pressure. Since rhe pressure of compressed
air is less fabout l0 barr, force develop€d is also less.
Pneumatic sysrems are faEter in operation because. air has
v€ry less viscosity. It can flow very quickly. Air rushes into
tbe cylirder once the valve is opened and within Do tiEe, tbe
cylinder ext€nds.
If coropressed air is readily available in the industry, then
pneumatic system is prefeEed.
Itr trlady industries, air compreBsor plant i_s alrcady installed,
as compressed air is needed for ditrerent processes. ID such
case, we can use the compressed air for operating pneumatic
system.

1.1.1 Advantages o, Fluld power Systems :

1. Fluid power syst€m avoids mechaDical linkages (such as

belts, pulleys, chains. sprockets, geais etc., to a greater

2 Hence, breakdowns are reduced and will incr€as€.

FoductioD
lql rFP 1-3 Basics ol Oil

t, 'Desisn ald constructioD" of Fluid power system is easy'

as pipes are flexible can be bent and
"I-rf?'*a1"-r""r'
accommodated in the available space
Automatic and salety circuits are possible' which is
very
4_
iripi:rt""i ,. *"**; rate of pioduciior and safew to avoid
accidents.
5 Fi;t; ;"".. svstems are more nexible to cope'up with the
il"i;';hilA Anv modification in desip can easilv
imolemeoted in the existing and fluid power system
6. v;ri*,r." -a noise, wear and tear etc a_re reduced' as tbe
mechanical liDkagps are replaced by pipes'
7. If thJ svstem ;talls TlIe svst€m sta-rts working
"""d".a"a,
once the load is reduced.
8. Maint nao"", lubrication etc aie simple and easy'
""."i"i"g,
1.1.2r Appllcatlons oI Fluid Power Syslems :

Fluid power systems involve hvdraulic and pneumatic

systems-

AI Applicalion ol hyd.aulic systems

1. Machine tools : CNC 6schine, hydraulic shaper etc'
2. Mat€risl haDdti[g equipments : Elevators, forklifts etc'
3. Construction field : Earth moving machines
etc'
4. Automobiles : Hv&aulic hake, hydiaulic ste€ring
gear etc'
5. Aircrafls : tlight controls landing
6. Railways : Hydraulic brake. suspensioD et('
7. urti"" n"fa', Ship steeriDg mechanism' sbip building
B] Applications ol pneumatlc syatoms :
1. Poeumatic tools: Drilling machine' nut runner' screw
driver et .
2. PacLing systems : Packaging
'nachines'
3. Mat€riat haDdling : Clamps, conveyo$' mbotic arms'
4. Mining : Pneumatic t{ols are us€d'
5. Auto6obiles : Ai bnke, Air suspeDsion etc
6. Machhe t ols : PneuEati€ press, clamps' vices etc'
7. Medical and dental equipfients : Dental chair'
oPerating table, Dental &ill etc'
fQZ] trp rft.lserrr 1.4 Bascs ot oitHyd,au,E Svstems

1.1.3 Ditference between Hydraullc System and

Pneumatlc System :

s-2012, W-2011
o. Diflerentiate between hydraulic system and pnoumatc sysl€m.

No- Eydraulic Syst€rn Pneu-matic Syst€m

I Working fluid i6 hydraulic Woiking fluid is compressed
oil
As oil is itrcompressible, oil Air is comprcssible; hence
can be pressurized to very air can be pressurizd to
high pressure. (500 bar or lesser pressure. (Ody up to
10 bar eppmx.)
3 Since pressure is high, force Since preasure is very less,
developed is also very high force developed is very less
(thousands oftons). (up to 1 totr)
1. Since pressure is high, CoEponents of ptreumatic
components are very strong, system are light€r ir
made ofsteel snd are heavy. weight, are made oI

5 As oil has more viscosity, it Air has very less viscosity,

cannot ,low fast. HeDce it cstr llox, fast. I{ence
hy&aulie systeas are slower Pneumatic systems are
iD operatioq. quicker in operation.
6 Due to continuous Harder it ruDs, cooler it
recirculation, t€mpemture of works. Frce expatrsion ofair
in cylinders alld motors
causes chilling etrect.
7 Hydraulic oils ar€ petmleum No chance of fire hazard.
based oils; they are Hence p[eumatic tools arc
inflarnmable and tiere is preferably used inside
every chance of fire hazard, mines, vrhere flammable
if neglectpd. ga$es may preaent.
8. Leakage of oil rcsults in Very clean aDd dry
dirty and Blippery surToullding is maintained.
surroundings, may lead to
accidents.
l,Ef ,..,.,""r., 1-5 Easics ol OrlHvdraulic Svstems

No. llydraulie Syst€m Pneumatic SYstaE

I Puop used is PoEitive No need of pressure relief
displacement PumP. So,
prcssue relief valve i3

10. There is tro need of separate Lubricator is ne@ssary. Oil

lubricatioD system, because, is mixed rvith the
hydraulic oil itr€f is a compress€d air in lubricator
lubricaIIt. and then supplied to the
sYstem

11 Applications : CNC' Applicstions : Mst€rial

m'chine t ols. earth moving handlhg systcms, hatrd
mschines, automobiles, toob minrng works,
aviatron etc. automation, automobiles

In hydraulic systems, oil under very high pressure is used for

obtsiaing huge amount of force. Hetrce the hydt'aulic components
prcssu,e. I'lEy
are made stronger eno ugh to withstand the high
are made of alloy stcels. The pipes, t}e valves and everything
of
hyclraulic system are strcag atrd heaw'
In pneumatic systems, compressed air is used; it is of
pr"""rt
-.r" ooly upto 10 bar (approxiEate) Pneumatic componeots
..a" tilt_ i., weight, are of less cost They are made of
aluminiuD, Pla.stic etc.
1.1.4 Ditlersnce between Hydraullc Motor, Air Motor and
Electric Motor :
w-N11
O, Dillerentate between air motors and eloctric motor'
w-2012
hydtaulic and
O, State any eigttt points of dlfferentiation bstw€en
poeumatc motor8.
w-2011
motor
O. Difterentiate ait motor with electric motor and hydraulic
w h resp€cl to medium used, speed control' weEhvpower
ratio, and
 14 Basacs ol Oit

Sr. Electricel Eydraulic Air Mot r

No. Motor Motor
I Danger of electric Electric shock Electric
proof. proof.
2. Danger of sparks Danger of fire No chsnce of firc
due to which fire hazard due to hazard. Bett€r in
hazsrds. leakage ofoil.
:l It takes more. It is very slow for It is very quick
time to pick
up its operation. and fa.st
the speed. operatiotr.
1 Design and Simple in design, Very sinple iD
conatmction is but .iSd in cotrstructi.rD sDd
complicate and construction, desiga, cheapr ir
co3tly. mediuE cost.
If run for longer ltre temperature Eader it ru4
time, its t€mp. incr€ases cooler it works.
SOeS oegligibly due to this is because,
on
iDcreasing, which friction. But the expanding air
may be dangerous doe$'t creat€ aay iu the moto,
to the wiDdings. serious prcblem. createa cooling
efect.
6. It can not b€ u.sed It should not be Due to the above
in hot in hot property, it can be
surrounditrgs. surroundings, oil used in hot
Windings may viscosity reduces surroundings of
butD out. with increase in temp. up lD
teEperature. 125 "C
7 Dust No conosion. But Absolutely
and dust
moisture damage oil and dust mske resiBtant atrd
it seriously due to the place dirty
and slippery. resbtant.
8. l,ess Noise Less Noise Noisy unless its
exhaust port
muflled.
Ef ,r" (trsere) 1-7 Basics oi Oil Hydraulic Sysiems

I 2 Hvd raulic System

Hvdraulic svstem is a power transmEsion systeE in which'
traasmiision ofpo*er ts}es place *uou8h the hvdrsulic oil

ri8. 1.2.1
qad rat'e
Power transmitted is the product of pressure of oil
of flow ofoil. Pump converu the mechalxical ener$/ int' hydraulic
fori of pressure and rat€ of flow Hvdraulic oil
"".L l"ttti.tft"hvdraulic energ] from pump to sctuator' Actuator
"r-i?"
converts back ibe hyaraulic eoergr irto mechanical energy'
1.2.1(A) General Layout ol Hydraullc System :

9m11, W-201r, W-2013

o- Draw genoral Layout ol hydraulic system and labol it'
w-2014
o. Oraw and explain the wo*ing ol hydaaillic system with its
general layout

Fig. 1.2.2 : kyout of general hydmdfc svstem

 @1,." 1u."r.y 1{ Basics ot Oit Hydraulic Systems

'1.2.1(B) Components
ol Hydraullc System:
92012
o. wrbus componsnts of hydraulic system? E(Illain.
\rrhat aro
92012
o. What is the tunction ol (1) ojt tank (2) Actuators (3) pump
(4) Filter.
s-tu13, W.N13
Q. Lisl out main elements of ic circuit

Basic hydraulic syst€m has the following components

1. Oil reservoir 2. Rotary pump

3. Pressure relief valve 4. Direction control valve
5. Flow control valve 6. Double acting cylinder
7, Pressure gauge 8. Filter
l. Oil Reservoir
. Maid fuDction of "oil reservoit, i_s to store sufrcieEt
amount ofhydraulic oil in the system.
. Apart ftom this, it has other impottant firnctions such
aa:
(a) To cool the hot r€turn oil.
G) To settle dowtr the coDtamhants.
(c) To remove air bubblee.
(d) To sepsrat€ wat€r froh the oil etc.
2. Rotary pump :
. The function ofrotary pump is to pump hydiaulic oil to
the hydiaulic circuit.
. It converts the hecha cal enersr (rotatioD of sha.ft)
ilrt hydreulic ener$a (pl€ssule and llow rate).
. Rotsry pump fu a positive displ&cemedt pump. It caD
deliver constant flow even at hgh plessur€.
 IFP (MSBTE) 1-9 Basics of Oil

3. Plslsur€ r€lld valvo :

. It is aD iDportaDt comDotreat Phich i6 r€quired for
every positive displaceDeot pu.Ep.
. This valve is conoec-tcd at the outlet of PuDp Its hain
function is to rElease the oil back to t€.aL whetr the
pr€ssure iocreas€s beyotrd pre€€t value.
4. Olrrctlor conlrol vrlv. :

It controls the dil€ctiotr of flow of oil, by which it performs

exteD-siotr aDd r€tractio! of the actuqtor (double acting
cylinder).
5. Flow codrol valw :
It coDtrots the rat€ offlow of oil, by which, speed of exteDsion
or retraction of actuator is controlled.
6, Acturtor:
. Actuator pmduces work. There are two t}?e8, linear
aduator aDd mtary actustor'
. Linear sctuator is calted cylinder, rotarjr actuator i3
called motor.
. Double actitrg cylioder is shown in figure 1.2.2.
r Cytinder develops force and mohon. It crtrverts
hydraulic energr in to Eechanical eDei8J..
. Force developed = pressure ofoil x Aree ofPistoE
7, Pr€lrul! gluge :
. It is an import$t coEPonetrt ofhydraulic system.
. It shorcs the pressure reading.
. PEssure settings are made by looking st the pEasur€
aauge.
. Without pressurc gauge, it is not Possible to make tite
presstrlr rclief valYe settin8E, uloading valve 3ettin83

8. Flltlr:
Its main functiotr is to r€move susPeadd solid coDtsoinat€s
froE the oil and to Fovide clea[ hydraulic oil to the system'
@f ,rr 1rsrr.; 1-10 Easacs ot Oil Hydraulic Systems

1.2.2 Applications of Hydraulic Systems:

s-2t 12
O. Write any tour applicalions of hydraulic syst€m
$2013
O. Enlist lour of
1 Machine tools I
CNC (comput€rized Numerical Cootrcl)
machi!€s, hy&.aulic pfesses, hydraulic shaper, et .
Meterial haodling equipEents : Elevatols, forkliftB,
cranes, lifis and hoists etc.
3 Conatnrction Field : Earth mo\ring machines such a.s
excavators, cranes, dozers, loaders, dumpers, tippels, trucks,

1 AutoEobiles :
Hydraulic brakes, hydraulic st ering,
hydmulic suspension, hydraulic clut h, hydlaulic power
tiansmission, hydraulic coupling, hydmulic torque @nverte!,
etc.

5 Mat€rial t4sting laboratory : (IIM (universal testiDg

machine) and other destructive t€sting machines, BP (burst
pressure) t$ting machine etc.

6. Aerospace : Landing gear, brakes, flight contmls (such as),

c6rgo loading door, Rudder, Elevator, Flap, AileroD, etc.

7. R.ailsays : Hydraulic bBkes, hydraulic steerhg, hydraulic

suspension, hydraulic clutch, hydraulic power transDissiotr,
hyd.aulic couplirg, hydraulic tolque convert€r, etc.
8. M.rrin€ field : Ship st€ering syst€m, ship yarde, ship
buildidg
I Medical equipmente : Medical chairs and operatina tables.
10. Agfcufturd EquipEent6 : Harvest€r:s, hactors, field
spra5'em, eeeding machine, fertilizer machitre et .
ffi ,r" (r""r.) I -1 1 Basics of Oil Hydraulic Sysler ns

1.2.3 Advantages ol Hydraulic Syslems:

$2011
O. Write the merils of oil hydraulic system.

s-mr1
O. Usl any lhroe merits ol hydraullc systom with reasoning.

1 Since hydraulic oil is i[coDprersible, oil can b€ Fessurized

to very high value, hence hydraulic eystems can develop
hugo emount of force (tDD6 together).
2 Due to viscosity of hydraulic oil, hydraulic systems arre
€lower in op€retior. Poid to be not€d is, slower speed is
morc sdvantageous for heavier jobs, and it lessens the
chaDces of acodents.

3 very precise speed contml i.s achieved.

4 If overloaded, the system stalls. System will Bbrt *orking

agEin once the load is reduced.

5 Automatic and safety circuits ale possibl€.

6 Hy&aulic systems are eelflubricating. ther€ fu no need of a

s€paratc lubricati0g BFt€m.

7 DesigD aDd constructiotr of a hydiaulic s,€tem ia very easy

and simple, pipes csn easily be bent aod accommodat€d iD
the svailable space.
ffi IFP (MSBTE) 1-12 Basics o, Oil Hydraulic Sysiems

1.2.4 Llmltallons ol Hydraullc Systems

*2011
O. Write lha limRations of hydraulic system.

s-m11
o List lh.ee demerits ot with

1. Leakage of oil causes dirty surroutrdings, slipp€ry floor,

increased chances of accidents.

2. Hydraulic oils aie p€tmleum based oils; hence there are

chances offire hazsds.

Hydraulic systems should not be operat€d at hot

suEoundrDSE. Because oil may become overheated, its
prop€rti* may destroy, oil may becoEe conosive, snd oil
may evaporat€ and may cst{h 6re.

4. Hydraulic syst€ms arc slower in op€ratioD; slow speed may

be a disadvantage if higher rste of work is desircd.

5. Operators working with hy&aulic syst€os should be

extremely cautrous; tiey should be given appropriat€
trainiag r€garding safe8 aspects. One should treve! neglect
the in8ide pressur€ of oil a.nd the force of the leaked jet of oil,
it hay cut the entire huDaD body into pieces.
gZ tFP I MSBTE) 1-t3 Basics oI Oil Hyd raulic Syslems

1.3 Properties ot Hydraulic Oil

1.3.1 tla$ Dansty

MasB deffiity is defitred as the mess of the Iiquid per unit
volume. It is denoted by " P "
MaEs of tiouid
Maas denBrty or Dquro = volume ofliquid
Its utrit in SI Syst€ms is Kglng
Mass deGity of water is 1000 KYE3

1.3.2 Weight Density

Weigit density (specific weiSht) is defired as v.'eight of tlle
tiquid per uait volume. It is denoted by "tr". lts unit itr SI
Systeme ia N/m3
weisht of li4!g
Weisht deosity of liquid = V"lffi; Uq"id
"f
Its unit in SI Syateos is N/m3
weight deDsity ofwatpr iB 9810 N/m3

1.3.3 Specilic Gravity

Specific gravity(rtletlve density) of a liquid is defined as
tlle ratio of density of that tiquid to deffity of water. It is denot€d

It is a ratio and hence it has no unit.

Mass deasitY ofliquid
Specrtrc grsuty oI llquro = Mass density ofc,atFr
Weisht density oI liquid
= weight density of water
Specific gravity of watcr is 1, Specific gravity of Dercury i3
13.6
@f ,r" 1rs"re1 1 -1 4 gasics o, Oil Hydraulic Systems

1.3.4 Compressibillty
It is the sbility of a fluid to get compressed. Gases 3re eorc
compr$sible and liquids are less compressible.
Compreseibility ia the reciprocal of bulk modulus. SI unit of
compressibiliB is m'1lN
Consider a pi-stoa cylinder arrangement aE shown irx
Fig. 1.3.1.
Let pr be the initial pressur€ and Vr be the iDitial votume of
the fluid before compression as in Fig. 1.3.1(a).

E E
-
(r)
Itg. l3.l
I

(b)

Now, cotr-sider a force of F is appUed on ttre pistod as showD

in Fig. 1.3.1(b).
Ipt p? is the final pressure and V, is the final volume of the
lluid alier compresaion.
Change in pressure = dp=pz-p,
Change involume = dV = Vr -Vz
/ Vr-V,\ ravr
Chaoce in volume
vorumetnc stram =
G6ii6iGi --t- I = [q] 1
Burk modurus rrr = q+E++EE+s =
dPN
volumetfrc Etrarn dV
( )

uompressrDrlrtv
fl \ VoluDetric strai!
e[*g" - p*""r*
lx./-,
IE J = = dPN
ffi ,r, (rrsu.e) 1-15 Basics ol Oil Hydraulic Syslems

1.3.5 Viscosity
s-2013
O. Deiine the term viscosity
Viscosity is defined as resrstance offer€d by the liquid to
flow. That is, some liquids can flow easily and some cannot, it is
inlerent prcperty of the liquid and this reaistanc€ t Oow depends
on some other physical prcperties such as t€dlp€ratur€, Pressure,
etc.
Nowton's law ol vlscoslty :
It stat€s, 'The shear stress otr a layer of flowi[8 liquid is
directly prcportiotral to the rate of shear stlain."
Ne*.ton's laer of viscosity says tlat
Shear stress * Bate ofshea.r strain
du
t-d:-
By inttuducing a pmportionali8 conBtsnt (P) ir this relation,
du
r = uxdy
1.3.5.1 Dynamlc viscoslty :
It is also called "absolute viscosit/. In siDPle words, it is tlre
proportionality constatrt itr equatioD ofNee.ton's law ofYiEcosity. It
i-s detroted by 't1".
It is defined as the sheat stless p€r unit rate of shear stlain
Shear strtess
Dynamic viscosity = Rate olshear shair
B du
( dy )

1.3.5.2 KlnemalicVBcoalty:
Kinematic viscosity is deined as the mtio of d)'tramic
viscosity to mass density. It is denot€d bv Y. ItB unit in Sl
Syst€ms is;.
Dynamic
KineDatic viscosit (Y) = Mass density p
Eff ,." (Msere) 1-16 Basics ol Oil Hydraulic SFtems

1.3.5.3 Grades of Hydraullc Oll :

ISO Gradsa :
lte int€mational Standard Oryanizatiotr (ISO) has
estabushed a table of ISO grsdes of oils bss€d on tbeb Lioematic
viscosity (in cst) at standard tcEp€ratur€ 40'C.
r For exanple : 150-46 gmde oil has kineEatic
viscosity of,16 cst (centi-Stokes) at 40'C.
. Difrerent ISO Grad6 are ISO-10, ISO-15,ISO-22, ISO-
32, 150-46, 150-68, ISO-100, ISO-150, ISO-220, and so
on,

SAE Gradea r

The Society of Automotive Engineers hae established

stsndards to specify the hydraulic oils/ensine oils.
. WiDter gr.des are givetr by tests conducted st 0'C.
For example, SAE-oW, SAE-10W, SAn-2oW etc.
. Summer Srsdee arc giveD by tests codducted at
100.c.
For example, SA.E-20, SAE-30, SAE-40 etc.
1.3.6 Viscoslty lndex (Vl) :
s-2014
O. Deline viscosity index.

Dollnltlon:
"Viscosity Index is an arbitrar.y numb€r giveD to hydraulic
oit corresponding to its chang€ in viscosity vrith iespect to chang€
in temp€ratur€".
r Greatcr the viscosity hdex, the less€r will be the chang€ in
viscosity with rcspect to chanae in temperature.
. Vtucosity Iodex should be as high ar possible for hydraulic
oil.
. ViscGity Index is a unit less number. It indicates the
tempemtur€ dep€ndency ofviBcosiry of 6ven oil.
Viscosity Inde! is given by,
/v^-r*)
VI. = \ -::----= I
Ya - YE ,/'r.o'c '
100
&T IFP (MSBTE) 1-17 Basics ol Oil Hydrau lic Sysl6ms

Where, V( is viscoeity bder ofthe given oil.

Y^ is Linematic viscositv of oil A at 40'C
Yi is ki.Eehatic viscosity of oil B st 40'C
Yr is kiDematic viscosity ofthe
given oil at 40'C
. Oil A and oit B ste trro refeEnce oiLs cbose! such that,
(s) vI ofoilA = 0, and VIofoilB=1fi)
(c) At IOO'C, kinematic viscooity of all the tbee oil8 is
aatDe.

1.3.5.1 Proc.dura to Datarmlna Vl ol Glvon Oll :

1. Kinematic viEcosity of the Siven oil is measured lor 4o"C and

100"C. Tbat is, t o and Yrm 6re rDeasur'ed.

2. For the value of the value6 of 1^ro atrd

Y,r@, YEro are tafeD

Eoo ASTM - D2270 tabte (Soe ApPetrdix A)

3. vI is calculat€d by the formula

/l^-rx\
vI' = lr^ - tt- J. ." x too

o. Calcuhte Ut€ vi6co3lty indox c, oil whos€ kinsmatic viscosity is

i 74.2 mm?s at /O'C and 1 2.2 mm% at l OO'C

Given : From table D2270,

For 1,,- = 12.2 ldm2/s ^trlo= 2O7.8 nmzls

l,n= 12.2 m$zls Ysro = 110 7 mm'A

14' = [ r^-Y" .J.,."."' loo

207.a - 174.2
x 100 = 34.6
= 207.8 - 110.7

Viscosity iader of the given oil is 34.6.

ffi IFP (MSBTE) l-18 Basics of Oil Hydrautic Systems

1.3.7 NeutralizalionNumber
92tt14
O. Detine neutralization numb€r.
Due to contamination, the oil becomes acidic. For its use in
hydraulic systees, it should not be acidic. The trumber of
Eilligrams of potsssium hydroxide (KOH) required to neutralize
one gram ofoil is known as Neutrulization Numb€r.

1.3.8 Flash Polnt:

It is defined as the temperatu€ at which the oil gives-of a

momeDtary llash. The flash point should be as lov{ as possible for a
good hydraulic oil to prevent fire hazardE.

1.3.9 Flre Resistance:

It is the Foperty, which rcsisk buming. Fluids, which are

firc rcsistant, are difficult to ignite. They do not support
combustion and propagation of flame.

1.3.10 Oxidation Stablllty :

Oxidatiotr iB s chemical reaction in which oxygen combines

with another element. lD hydraulic systems, oxygen from
atmosphere combiDes with the oil. Due to oxidation, t}le desirable
prop€rties of hy&aulic oil will be sever€Iy affectcd. Hence oil
should have high degr€e oI oxidation strbility (i.e. rcsistance to
oxidizel

1.3.11 Lubricity:
s-ml3
O. De{ine the term
It is the ability
of an oil to r€duce fi.iction and wear tretween
moving compoaents.
Lubricity will reduce wear and tear ofcompooetrts power loss
due to fiction and increase the life oftle componeats.
ffi ,r" (rsrt.) 1-19 Basics ot Oil Hydra ulic Syslems

1.4 Required Properties of Hydraulic Oil

Selection ot Oil (Requ ired Properties oI Oil):
w-20r2
O. Deline lour ol lluid.

Follo*'ing are the required Fop€rties ofhvdraulic oil

1. Oil should b€ incompressible, i.e. it should withstsnd high
pressure so that we can obtain huge abount of force at the
actuator.
2. Oil shoutd have sufficietrt lubricating Proporties 3o as to
rcduce wear and tear.
3. Oil should hsve satisfactory viscoslty iDder so tist it will
perform under oPerating tempemture extreEities.
4. Oil should be cheaicslly st ble, so that it will not teact
with any otler subBtances.
5. The pour point ofoil shoutd be a-s high as Possible so that it
E'ill not solidiry at bw operating t€Epetatur€. Pour point of
oil should be at least 15' F below t}le lowest operating
tempcratuie.
6. the flash Point ofoil should be as hiSh as possible so as to
prcvent fue hazards.
7. The oil should not be scidic so that it will not corrode the
metallic components.
8. I'he oil should have good oridetion rerisbnce.
9. The oil should have enti_wear and anti'rust Properti$'
10. I'he oil should be non'toxic so that it wiU not afrect
operato/s hands.
11. The oil should have snti'foa.E proPerties so that bubbleg
and foam will not be formed

12. The oil should have good del[ulsibility to separate out

wat r contained in it.
Eff,t" (u."r.) 1-2O Easics of Oil Hydraulic Systems

1.5 Pump
Pump is a Dechanical device phich gives energy to the
liquid.
Liquid caD have the eners/ in any of the three forms naDely
kinetic energy, pressur€ enersr and pot€ntial energ/.
thus we can deflre a pump as a mechanical device which
. makes the liquid tD flow,
. will increase the presawe ofliquid or
. will lift the liquid iiom lower level to higher level.
lmporta concept to know :
. lD fluids, conversion ofenergy is autooatic dep€nding on the
situation.
r If there is no restriction, Iiquid flows easily with high speed,
hence kinetic energr is more.
. If restriction (opposition) to flow is mor€, then velocity
Educes and pressure increa.s€s.
. If liquid i6 allowed to ri,se in a verticsl pipe, then f'otctrtial
enelgy will increase on account ofthe pressure energr,
. According to Bemoulli's theoreE, the sum ofure t}uee forms
of ener$/ remains constsnt.
. hessure eaerSy + kiDetic energy + potential energ, = c5ngtail
1.5.1 Cla8sttlcatlon ol Pumps :
w-2014
O. Givo tho classification ol

Posfivs Disfiacomenl pump Non positive displacemenl pump

f ------l
I

Recaprocating pump Roiary pump CentdJugalpump Ariatpump

@1,t" (r"ut.i 1-21 Basics ol Oil HydraLrlic Syslems

1.5.2 Positive Dlsplacement Pump (PDP) :

w'2012
O. What is meant bY PDP ?
Itis a pump whose aisplacement (dischsrge) tu positive'
Here, the word 'positive" ioPlies that, definit€ly t'here wil!
b€ definitc smount of discharge irrespective of increase in
pleasurc.
Whstever 6ay be the prcssure, the pump diecharge remarns
the s3me.
Only such pumPs can be used for hy&aulic sy8tems,
because, hydraulic syst€ms have to develoP larEe amount of
folce, fo, which lar3p amount of pressure is rcquired, and
only PDP can deliver discharge under high pressure'
1.5.3 Non PGltlve Dlsplacament Pump (NPDP) :
92013
O. What do You mean bY NPDP?
In case ofNPDP, the discharge does Dot remain coNtsnt'
Discharge teduces witlt increase in pressure and discharge
becomea zero at BaximuE PressuE.
At higb pr€ssue, the pump can oot deliver oil HeDce NPDP
is ofno use for hydraulic systema.
1.5.4 Worklng Prlnclple ol PDP and NPDP :
For this, otre has to u[derstand the conBtruction of the3e
Purtrp8.
Incase of PDP. the trroYiDg comPonent of pump carries the
liquid fromir et to outlet.
If movin8 co6poneDt Doves, theD t}te liquid has to move'
there is no other way
where a3' in NPDP, t'he high speed 6o\ring compotrent
(called impeller) gives off its kinetic ersrgv to the liquid'
I'he liquid tskes that kinetic enerEv, and with that KE it
Doves froD inlet to outlet.
 1-22 Basics of Oit Systems

. But ifthe oppositrg pressue at outlet is mo!e, thetr the KE of

liquid b€comes insuficient to overcome the opposing
preasute, and the liquid cannot Eove. As there is more
clesrance gap b€tween imp€ller snd casing, ttre liquid etatts
rotstitrg witlin the casing.
. Hence only PDP can pump oil at high preseure and NpDp

1.5.5 Rsaaons lor not ualng r€ciprocs ng pump ln

hydraullc systoms:
. Reciprocating pump hs_s more number of moving
compoaents, piston, crank, coDnectiDg rod, valve etc.
. Due tD tbi.s, cost is more, size is more and mahteaa.ace cost
is more.
. Reciprocating pump has reciproc{tinA parl!.
. Due to this, lot of vibration s.nd aoise is
Foduced, stroDa
foundation is requiEd to absorb the vibrations.
. Due to lluctuating load, pu.mp can dot be directly connect€d
to motoi shaft. Belt-pu ey arratrg€meot is requipd to sbGorb
the fluctuations in load.
. Fb'wheel is rcquired in order to uniform the fluctuating load.
. Due to flrrxheel, belt pulley arraogemeat, craDk, c\onnecting
rod eta, the overall size incrcases. Reciprocatbg pulDp is
bulky.
. Discharge is there during every delivery stroLe. There will
not be any discharge duriDg suction stIoLe.
. Due to this, the pressure and discharye ar€ fluctuatitrg. Air
vessel is necessary in order to daDpeo the fluctuatiotrs.
. CoD-sidering the above said disadvantages, it is clear that,
the reciprocating pump is not at all suitable for hv&aulic
systeEa.
ffi ,t" (r""-.) 1-23 Basics of Oil Hydraulic Syslems

1.5.6 Reasons lor Preferring Rotary Pumps in Hydraullc

Systems (Advantages ol Rotary POP) :

w-dt 2
O. List any lour advantag6s ol POP

9Z)14
O. E,qlajn why ooly rctaty pumps ars prer€ned for oil hydraulic

. Rotary purops are positive displacement pumps The rate of

flow (discharSe) of rotary puop remaiDs mnstatrt
irespective of prcssure. Ihat iB, eveD at very hiSh prcssure,
these puDps can give the same amount of discharge lhe8e
pumpe can dweloP very high Preeeure.

. The dischsrgp or pneasurre of rotary pumPs is sE(toth, not

pulsating. There is no need of atry air vessel.

. Very tess vibratiotr and troise i3 observed with these pump8

therc is tro need of stroag foundahon.
. RDtarv puDps are very coEpact lhey have leae number of
parts. Pump is directty codnected to motor shaft'

. Cost oftot$'y pumps is coDParatively less.

. Maintctrance is easy, and maiDt€na.Bce cost is less'

. Rotary pumps do Dot have rcciprccating codponents Hetrce

thele will not b€ fluctuating loads. HeDce, flywheel tu not
required.
CoDsideritrg the above adv6.shges, rotsry putrps are
preferred for oil hydraulic systems.
 ig IFP (MSBTE) 1-24 Basics ofoil lic

1.5.7 Comparlson between pDp and NpDp :

92011, W-4)11
o. Comparo Positivg Oisptacem6nt pump with Roto-dynamlc

8r. Po8itive disphceoert Non-positivo didpleceDent

No. pumP pump (R,oiDilinanic PuDp)
1. ID mP, the moving In NPDP, the moyins
compoaetrt c€r'ries the component gives ofr its ener$/
Iiquid alo,rg with it IioB to the liquid, due to this; the
i et port to outlet port. liquid will be tttown froo inlet
porb toward-s outlet.
2 In PDP, discharge In NPDP, as prtessure incr€ases,
rcDaina cotrstsDt discharge reducet atrd become
ir€spective of incf,erse in zero at m,;hnh prcs$uc.
pneaaune.

3 Less tlischarge, More diEcharge, less pressurc,

high sp€ed.
--t_-
4. Priming i-s not Decessary Primitrg is necessary for NPDP
for PDP
5. Foot valve is Dot needed Foot valve i6 treeded for i{pDp
for PDP
6. ID PDP, ttre delivery valve In NPDP, tie delivery valve
should trot be closed vhile should b€ opened slowty oDIy
the pump is ruDning. after max. preseure is reached.
7 Prcssur€ relief valve is Preseure rclief velve is lot
nec$aary as a safety needed, becaua€ press(u! does
device iD order to safe not incr€sse beyond certaia
guard system compooents lidit.
8 Elamples are: ExaDple6 are: Cetrtrifugal
Recipmcathg pump, Pump, Aial pump.
Rotary pump: G€ai, Vane
and Pistotr t],!€ pumps
ffi rrp (rJsere) 1-25 Easics ol Oil Hydra

1.6 Classlticetlon ol Rotary Pum

s-2014
O. Give the classilication 01

Classillcation ol Rotary Pumps

G€er pumps :

1. Ext€mal gear Pumpe 2- intertral gear pump€

3. Irbe pump 4. Ge-rctor pump
5. &rew puutp
VaDe pumps :
1. UDbalsnced vane puhP 2. Balaoced vane PumP
. Pbtotr pump:
1. Axisl pistotr PumP
(a) Straight sxiB Ptuton PlrrDP
(b) Beot sxis Piston PumP
2. Radial ptuton PumP
(a) StatiomrY cylitrder tj?e
(b) Rotating cYtinder tfPe
1.5.1 ExtornalGoarPumP:
*z)13
O. Explain of Extemal Goar

0
Fig.l.6.1
l42l rpp orsere 1 -26 Basics of Oil Hydraulic Systems

Fig. 1.6.1 shows ar extemal geat pump- It coDsists of two

spur or helical gear€, which are meEhed with each other and
mourted iEide the cssiDg.
One is driver and other is alriven.
When th€ driver is mtsted by meane of any prime mover (i_e.
electrical motor), driven will also rotat€.
ltus paitial vacuum is creatcd at the idet of the pump.
Oil is forced to eDtrr the pump by atmospheric pressure.
Oil.is trapped in the pockets betweetr teeth and the casing
and carried toi,ard6 the outlet porr.

1.6.2 lnlernal Gear Pump:

It has two gears, one is haring external t€eth and the other
is having int€rnal tceth-
The ext€rnal gear is inside the irrterDal geal. The two geals
are iD mesh with each other. A crescent seal is provided
b€tween these two gears, ehich fiIs the gap between the two
gears.

Flg. 1.6.2

A.s the t€eth of the geais comes out of mesh, a partial

vacuum is created, snd hence oil fiIls io the pockets between
gear t€eth and the crescedt seal, trapped there, aad carried
from inlet to outlet.
@l ,r, (rsutr) 1-27 Easics oJ Oil Hydraulic Syslems

1.6,3 Lobe Pump :

s-2014
O. With a neat lhe lunclion ot lobe

Thi! pump is similar to extemal Sear pump.

It consists of two rotors, one i-s driver and other is alriven.
These lolors have very leae number of teeth' (may be two,
three or four) aDd they are in mesh with each other.
Due to less aumber of t€eti, hiSher discharye is achieved.
Figure shows s lobe puhp with three'teeth' irt each rotor.

Fig.l.53

When the <lriver lobe is rotated by means of any prime

mover, driveo lolr will alao rotate.
lhue partial vacuuD is creatad at the inlet of the pump.

Oil i.s forced to entcr the pump by atmospheric Prcssure.

Oil is trapped i! the pockets betweeD tceth and tbe casing
aod csiried towards the outlet port.
@,r, (u""r.) t2A Bqsics ol Oil

1.6.4 Ge-rotor (cenerated Rotor) pump :

s-2t11
o. O.aw the laboled figure of Ge-rotor pump. Exptain its workino.
w-2012
o. What is G€-rotor pump? Explain its working witr a n6at skotch
w-2r13
o. Explain wo*ing o, Ge-rotor pump with sketch.
w-ml4
o. mp with neal sketch.
This pump has two generated mtors as shown in the
Fig. 1.6.4. oDe is haviDt extcmal t€€th and orber is havitrg
int€rtral teeth
The rctor v{ith external teeth rotat€s inside tie rctor havitrg
htcrnal teeti.
The inner rotor is hsyitrg one tooth Iess thao that of outer

The inner rotor is drive! to which, the shaft of any priDe

mover is coupled.

€ €

Ii& 1.5.4
Consider the gap (1-2) b€tween the rotors a_s a pocket. The
size of the pocket goes oD i[cleasiDg as tbe rotor rotates.
'Ihus more a-nd more oil fitls in the pocket.
AIi€r 180" ofrotations, further rotatioa causes the size of the
pocket t reduce, callsing the oil to llow out of the pocket.
Thus, from oil is sucked in from iDlet port
duriry first -eq+
half of-pocLet,
rotation and oil is delivercd to outlet port
during the next half.
There are pockets; three of them are performing
-sir such
suction and while the rehaining three are deliveriirg the oil."
Hence the flow is continuous.
lql rFP sTE) 1-29 Basics ol Oil Systems

1.6.5 ScEw PumP :

. _two fu a positive displacemetrt Pusp' thic\
The scriew purBp
comes with or three sct€ws Each shaft has a left_hand
screw aird a right_hald screw, for hy&aulic pte8sur€
balance.
. A single scnew version cslled "progressitrS cavity pump'is
showD in Fig- 1.6.5.
orrrl.l

1t

I
I
N\\rSI Wilt
I
II

f
Inl€l
Fig. 1.65

. This pump has one inlet is at each eDd snd the outlet is in
the middle.
. While rutrning, liquid fiIs in tle gap b€tweeD the screws and
the casing and moves it aloag v'.ith the scr€ws froln iDlet to
outlet.
1.6.6 Advanlages ol Gear PumP3:
s-2014
O. Give lour ot
I Simplicity and comPactness
2 Less trumb€r ofPs.rts
3 Low cost
1 Quit€ in operation
5 High operathg spe€ds
6 Less sensitive to contamination
7 Gear pumps are rcveruible-
El',., (MSBTE) 1-30 Basics ol Oil lic Systems

1.6.7 Unbalanced Vane pump:

. It consists of a clindrical rotor, which is mounted $.ith an
ofset inside a circular casing.
. The vanes are seat€d in the radial slots of the rot r and held
against the casing by spring or hydraulic force.
. Hence there will not be any leakage oloil between the vane
tips and the casitrg.
. But still, there is some leakage of oit between the rctor faces
and the body sides. Hence its volumetric efficiencv wiI he
wound 95%.

Iner + * our
"r

Flg. r.6.6

As the mtor rotates, the size ofpockets goes on increasing on

left side and reducing on righr side.
Tlfs causes section of oil at left side aid deliverv of oil at
right side.
Difference in pressrrre between inlet a d outlet ports creats
a side thrust on the rotor shaji, which consequen y ioad
bearhgs. Due to this bearing life reduces.
This problem of side thrust on bearings is nullified in the
design ofbalanced vane pump.
ffi ,r" (r""-.t 1-31 Baslcs ol Oil Hydraulic systems

.1.5.8 Variable Displacement Vane PumP

w-20r3
o Explain !/ith sketch the working ol variabie displacement vane

This pump cotrBists of a cyliDdrical rotor with radial slot3

inside a reactioa ring. Vanes are insert€d in the radial 3lots.
As the mtor rotates, dre size of Pockeb goes on iEcrea8ing on
left side and reducing otr right side.
Ttris csuses suction of o at left side snd delivery of oil at
right side
Spnng

rk. 1.6.7

An aduEting screw is provided to va.rv the discharge. By

turning this scr€w, the rcaction ring can be moved up or
down. This csuses the offset betwe€n mtor cetrtrc and
resctioD ring centre to chatrge.
By chstrgilg this ofrset, we can changB the pocket size, and
by cha[ging the pocket size, the discharge is varied.
@f ,," 1-32 Basics ol Oil Hydraulic Sysiems

1.6.9 Balanced Vano Pump :

In this type of pump two inlets a.od two outlets are employed.
Due to tiis, the equal andopposit€ side tlrusts gEt balaac€d
(nullified), aad hence thie type of pump gives bett€r Eervice
and longer life.
The center exis of the rotor and that of t}te eliptical casinA

0
C6sin9

+
odbr
fig. r.6"E

As the mtor mtates, tbe size of pockets goes od increaeing oa

otre side and reducing oD other side.

This cau.s€s suction ofoil at idet a.trd delivery ofoil at oudet.

ffi,.t BTE t-33 Basics oi Oil ulic

1,6,10 Stralght Axls Pleton PumP :

911
O. Explain axialpislon pump with neat skotci
w-drr3
O. What is the use ol swash plate in axi6l Fiston pump?
w.an1
o. ot axial with neat sketch.
It consisB of a cyliEder block tgith arial bor$.
Pistons aie insert€d ilr the bores, and the other end of the
pistoDs is connect€d to the shoe plat€ with shoe joints
(spherictl joitrb).
In straight axis piston puEp shown in figue 16 9, tie
rylinder block tu fitt€d to the dtive shaft.
The axis of rctqtiotr of rotstion cylinder blocL aad the ddve
ghaft are the same.
I'he sho€ plate is Eounted on a swash plate, which is 6xed at
an argle t, the axis ofmtatiotr. I]re angle of swash platc can
be varied to chaDg€ the di-scharge.

r
/
valvs Plai6
Uo.t
- Cvln b,
'
/ / 7P'M ,sto.or"te

+
od

.> I

n8' l'5'9
When the shrft is mtatcd, it causes the cytiader bloct
mtates, the shoe plate will also rotat€ with it' causiug t-he
piBtoDs to reciEoctt€ h the bor€.
ffi IFP (MSBTE) 1-34 Basics ol Oit Hydrautic Syslems

. Half rotatioo of the cylinder block causes suctiotr of oil into a

bore aild the next half rotstion causeE discharge.
. There sre 8 or 12 trumber of such bores, which are
contitruouEly perfomting suction and discharge in proper
order; heDce the pump dfucharge is smooth and continuous.
F\.ctioD ot swash platc :
. Su,ash plat€ is used to change the discharge
ofth€ pump.
. By changing the angle of swaeh plate, we can change the
stroke length, aDd hence the discharye.
. Yh9" swash ptate is perpndicular to the pump axis, the
discharge is zero.
. Dischar.ge itrcreases with increase in swash platc angle from
this perp€ndicular to pump axis.
1.6.1, Bent Axls pbton pump :
. It consists ofa cytinder block with axial borcs.
. Pistons are inserted in these bores. The other end of the
pistons are coDneded to the shoe platc with shoe joints
(spherical joints).
. In-betrt sxis piston pump shown in Fig. 1.6.10, the shoe plate
is fixed to a flange; the flange is keyed to a drive shaft.

Iig. r.6-10
The axis of cylinder block atrd that of the llaDge are
iDtersecting at an aDgle. A universal link couples the llange
and the cylidde, block.
ffi,r, (r"ut.) l-35 Basics ol Oil Hydraulic Systoms

. When the shaft is rotated, it causes the cvlinder block to

rotate, the shoe platc wiU also rctate with it, causing the
pistotrs in the bores to reopncate.
. Half rctation of the cylinder block causes suction of oil into a
bore and tlle next half rotation causes dischargp.
. There are 8 or 12 number of such borcs, wb,rch are
contiDuously performing suction and dischar8p in prcper
order; hence the pump diBcharge is smooth and continuous.
1.6.12 Stetlonary Cylinder Radlal Plalon Pump:
o Fig. 1.6.11 shows a stationary cylinder t}?€ ladial piston
pump-
. It coEsists of a stationary cylinder block, in which, five
cylinders are arla[ged coplanal with equal angle b€tween
them.

Fig.l.6.ll
. Totally there arc five pistoD-s, one rcciprocating inside each
cylinder.
. All piBtons are connected to a single crank by individual
coDnecting rods a-s shown in figure
. All suction valves are connectd to a single suction Pip€ and
all delivery valves are connected to a single delivery pip€.
. When the shaft is rotated by meaos of any prime mover, the
pistoDs n'ciprocste itr cythder atrd perforo suction and
ielivery of liquid in sequeoce. Pump discharge is smooth and
continuous.
@re 1-36 Basics ol Oil Hydrautic Syslems

1.6.13 Botatlng clllnder Radlal Piston pump:

. R tating Cylinder Rsdial Piston Pump is shown in
Fig. 1.6.12.
. this pump consists of rctating cylinder block. which is
mounted with an offset inside a cssiDg.
. lte cashg has a reaction ritrg with which, the pistoDs
reEains in contact while the cylinder btock is rotating. This
is achieved by centrifiEal force and preBsure ofliquid.

ng. r.6.12
The pistons are assembled inside the radial bores of the
cylinder bloch iolet port and outtet port ate located at the

The inlet port and outlet ports ar€ separatDd by pitrtle.

As the cylinder block mtates, pi-ston will reciprocrte in their
bores,
This caus€s suction of oil during 6rst half of mt tioD a.dd
di8charge during the next h6lf.
there are 8 to 12 nuDber of such bores, which are
codtinuously performing suc,tion a.ud dischsrge in proper
order; hetrce ttre puhp discharge is smooth snd cotrtiDuous.
m IFP (MSBTE) 1-37 Basics ol Oil Hydraulic Svslems

1.6.14 Seleclion Criteria tor Hydraulic Pumps :

w'N11
O. what are the selodion cdl€ia tor hydraulic pumps?
s'21t12
O. List out any four cdtoda tor sal€ctlon ol hyd6ulic pump in
hyd.autic system. Explain €acfi in briel.
w-2013
O. What are lhe crite a for selecton ol

Fsctorr to be considcred lor selection ol hydreullc puDp :

l. Preaaurt :
Gearpuops : 35 to 20o bar
vanepumps: 70 to 140 bar
Pistonpueps: 1'O to 850 bar
2. Ili*h.tge (rot4 offos) :
Gearpump : uP to 45 D3/hr
Vaaepump : uP to 20 m3/lu
PistoD pump : uP to 'l-5 Ds/ht
s. Speed:
Ge-rr pump : 1200 to 2500 rPm
Vanepump : 1200 to 1800 rPm
PistoD Pump : 1200 to 3000 rPn
,1. Volumekic e6ciencY :
Gearpump : 80to90%
Vanepump : 901a95 %
PistoDPump: 95to98%
1.6.15 Comparlson bsturrn Gear Pumpc, Vano Pump and
Plston PumP :

9201,
O. DiffErontiate betwoon gear pump and piston pump on th6
basis ol lunction, construclion, plessurc aarEe and Delivery ol
oi!.
@f ,re (MSBTE) l-38 Basics ol Oil Hydreu Syslems

Gear Pump Vane Pump Pkton Pump

Construction :

It consists of two It cotrsists of a Itconsists of a

gears in mesh s.ith cyliDdrical rotor rvtinder blocL with
each other, with radial slots. axial or radial
mounted inside a Vanes are inserted bores. Pistons arre
closed casing. One io the slots. The iftert€d id the
is driver and the rctor is molrnt€d \orcs. One end of
other is driven. $.ith an otrset in the pistol is
the casing. connected to
rotstitrg

Working (Function) :

When the driver is Rotation of Rotation of t}te

mtated by means of cylindfical rotor Eoving compotreDt
any prime mover, causes the size of causes the pistons
driven will also the pockets to grow to reciprocate in the
rotatc. thus the oil continuously on oae
is sucked, trapped side and to rcduce Hslf rotation of the
between seal t€eth or the other side cylinder
block
and casing, carried This causes frlling csNes suctiol ofoil
from inlet to outlet. of oil on suction iDto the bores and
side and delivery of the trext half causes
oil on the other discharge.
side.
Pr€ssure, discherge, speed s.nd voluEetric efficiency :
p = 35 to 200 bar p = 70 to 140 bar p = 140 to 850 bar

Q = up to 45 m3^r Q = up to 20 m3^tr Q = up t, 45 m3Ar

N= 1200 to 2500 N= 1200 to 1800 N= 1200 to 3000
rpm rpm rpm
Il-r = 80 to 90% 4,o\ = 90 tb 95% 0*t = 95 ta 98%
ffi ,rr (r""r.) 1-39 Basics of Oil Hvdraulic Syslems

1,6.16 Trouble Shooting ol Hydraulic Systems:

w-2014
O. I write the causes and remedies for the lollowing
(i) Excessive heat in oil
(ii) Noisy pump
(iii) Low pressure in system
Valves
Trouble Cause Rcmedy

1. Dirt in sy8t€D 1. Drain atrd flush

s,.ste6. Disassemble
and clea.n.

R€sponse 2. Pilot pressure low 2. Check pilot pre$ure

Stuggish 3y3t€m.

3. Maliunctions of 3. Check for pmper

source voltage and
frequency. R€move

1. Dirt in B,rt€m 1. Disassemble, clean,

and flush.

2. No pilot pr€Bsure 2. Check source of pilot

Spool ia
Mot Moving
3. Solenoids not 3. Check electrical
s,orking source and solenoid
fields.

1. I8prop€r 1. Check installation

drawiags.
Undesil'?d
Reapona€ 2. lmprcper assembly 2. Check pqrts and
ofvalves ttiawinga.
ffi,., 1r""r.y 1-40 Basics ol Oi lic Systems

Cylinders
Trouble R€medy
1. Valves sticking Check for dirt or
bi.ndinA SumrDy depGit.
Check for lPom psrts.
Check for
cont!minatiotr of oil.
2. Cylinder sticking or 2. Chect for dirt or
binding gummy deposit.
Check for worn parts.
lffatic Check for
Action n.baliglmeDt.
3. Pilot pressure too 3. Cotrtrol liDe may be
too smsll or DetcritS
valve lot ,orkitrg
properly.
4. Int2rnsl leatage in 4. R€pair or r€place
cylinder wom park and loos€
_!gs
Fluid Motors
Trouble Csuse Remedv
Rutr ng 1. Incorrect pipe 1. Check circuit and
W.ong corurection. corr€ct it.
Direction
Motor l. Reliefvalve is open 1. Remove dirt under
Rund,'g, Not pressure a4iustment
Developing ball or piston.
Proper Spood 2. Free flow bsck to 2. DCV Eay be in open
tank is being in center po€itiotr or
allowed in the any other r€turn liDe
Byst€m is opeD. Repair or
replace valve.
3. Driven mechanism 3. Bemove motor aad
binding because of checL torque
mis-aligDment requir€ment of alri\/eD
Bhaft.
4. Pump Dot 4. Check the pump
delivering delivery and
surmcieDt pressrr.re pressune.

Ett€r[d 1. Gaskets leakhg 1. ChecL and Replace

Leakasc of oil
@,,e MSBTE) 141 Basics o, Oil

Pumps
Ttouble Csure
l. WroD8 dir€ction of 1. Obe€rve arrow on
pump rotstiotr pump ca8e. Dilection
of mtatiol must
2. I,ow oil level 2. Fill rEervoir so that
surface of oil ie well
above end of suction
line during all ofwork
cycle.
Ercessive 3. PuDp running too 3. Rcduce speed. Speeds
Pump Noiee faBt above rating are
harmful and
eafly failure of
Pump6 Refer to
pump ratitrgr.
4. Coupliry 4. Re-aligD pump and
DisaligDmetrt motor accurat€ly.
5. Air bubbles in 5. Pmvide Eservoir with
irbke liDe baffles.
6. Wom or broLea
6. nephce
Parta.
1. Oil bpassing to 1. Test cir.cuit pressu&
progre$ively. Watch
fo! opeD-cetrter valveB
or other valve8 open
Pump Not
2. Defective pressure 2. Instsll prcssue gauge
Delivering gawq gauSe tioe is knowD to be acc-urat€
Preaaure
shut of. ia a line open to pump
pnessune.
3. Pump speed is less 3. Ch€ck minihuE
speed
rccommendationE
ffi,." {rs"-.) 1-42 Basics of Oil Hydraulic Sysloms

Ttouble Caus€ Remedy

1. Wrong direction of t. Observe arrow on
pump mtation pump case o,
nameplat . Direction
of hust correspond.

Punp not 2. Oil level low in 2. Maintain oil level in

r€Bewoh well above
Delivering bottom of suctiotr line
)rl at all ti6es.
3. Pump running too 3. Increase speed. Ch€ck
slowly minimum speed
recommendatiom t b€
sure ofproper pdmiig.

System

Tr.ouble Cause R€mody

pressure is high R€duce pump prcEsuie

Idle period oay be

Oil is beconring hot
morE, reduce it.

Insufiicient cooling
Install oil cooler.
facilities
Increase res€rvoir
capacity.

Belocat€ power uDit, or

Syot€m High ambient
baffle against radia[t
Exces3ivoly
heat.
Hot
BriDg level of oil up tD
I,ow oil in reservoir
r€comDeDded point.

Iutcrnal parts Bay be

Excessive friction
too ti8ht.

Increaae Bize or ilatall

Beservoir too sEall auxiliary cooling
equipEeDt.
EE] IFP (MSBTE) 1-43 Bascs of Oil Hydraulic Systeir-

'1.7 lmportant Examinatlon Ouastions and

Answers
Please refer ebook for complete solution

1 Please dnwntmd our free e-book for detaited. answers

of fo I ln u ing q ue st ion s.
2. All Questions & Ansuers couer the conplete chaptel

1.1 Fluld Povor Syst€m :

Q. I Differentiate betweetr hydraulic system and

pneumatic system.Isection 1.1.31 (912, W-l1, W-12)

Q.2 Difrereiltiat€ between air motor and hyalraulic motor.

tsection 1.1.41
OR
Q.2 Ditrerentiate between air motoN and electric motor.
tsection 1.1.41 (w-lr)
OR

Q.2 Ditrerentiate air motor with electric motor and

hydraulic motor with respect to medium used, speed
conhol, weighypower ratio, efficiency alld
applications. [Section 1.1.1] (W-r4)
1.S Eydraullc Systea :

Q. 1 Draw general Layout ofhyd8ulic system and lable it.

tSection 1.2.1(Nl (S-11, W-11, W-13)
OR

Q. 1 Draw and exptain the working of hydraulic system

with its general layout. tSection 1.2.1(A) & (Dl $l-t4l

Q.2 What are various components of hydraulic system ?

Explar,r. tsectinn 1.2.1(B)l (S-12)
OR
ffi ,r" (rs"r.) 1-M Basics of Oil Hydraulic Systems

Q.2 what is the tunction of (1) oit tank (2) Actuators

(3) Pump (4) filter.Isectinn 1.2.1(B)l (S-r2)
OR

Q.2 Name any four basic elements used in hydmulic

citc'uit. [Section 1.2.1@), ($r3' f,r-13)
Q.3 write any four applications of hydraulic system.
tsection 1.2.21 (S-r2' S-rs)

Q.4 Write the merits of oil hydraulic system.

[Section 1.2.3] (S.11)
OR

Q,4 List any tbree merits of hydraulic system lvith

reasoaing.
lsection 1.2.31 (S-14)

Q.5 Write tbe Iimitations ofhydraulic syst-em.

[Section 1.2.4] (S- )
OR

Q.5 List any three dements of hydraulic systems with

rcasoL,I.e. fsection 1.2.4] (S.14)

1.4 Prqrertlga of Eydraultc Oll:

Q. 1 Define the term iscos\ty. [Section 1.3.5] (S-13)

Q. 2 Define viscosity idex. tSection 1.3.61 (S-14)

Q. 3 Define neuhalization number.Isecrion 1.3.71 (S-14)

Q. 4 De6ne the term Lnbricity. fsection 1.3.11] (S-13)
1.4 nrqutrGd Propoltt63 of lljrdraulto (xl aobctton of O{l
(RoqElr€d ol (xl)
"roportt€
Q. 1 Define any four important properties of hydmulic
fluid. (W-r2)
1.5 PUED :

Q. 1 What is mea t by PDP ? List its any 4 advantagG.

[Sections 1.5.2 and 1.5.6] (W-12)

Q. 2 What do you mean by NPDP ? fSeclion .z.5.31 (S-13)

 1-45 Easics ol Oil

Q. 3 Comparc Positive Displacement Pullp with

Rotodynamic Pump.lsecrrbn 7.5.77 ($11, W-ll)
Q. 4 Why rcciprocating pump is not pr€fend for hy&aulic
s$tems? [ Section 1. 5.5 ]
Q.5 Explain why only rotary pumps are preferred for oil
hydraulic systems. lsecrion I.5.6J (S.14)
Q.6 Give the classficstion of positive displacement pump.
tsection 1.s.11 (W-r,r)
I .o ClaarlrloatloD of Bot ,ry Puryr :

Q. 1 Give the classification pumps.

of&tary (S-14)

Q. 2 ExpIaiD worLing of External Gear Pump. (S.13)

tsectian 1.6.11
Q. 3 With a neat skekh, explah the tunction oflobe pump.
[Section 1.6.3] (S-14)
Q. 4 Drarv the labeled figure of ce-rotor pump. Explain its
workitrg. lSectinn 1.6.4] ($rr)
OR

Q.4 What is Ge-mtor pump ? Explain its workitrg with a

neat Bketch.lsecrion I.A4l (W.r2)
OR

Q. 4 Explain gemtor pump with Deat sketch. (W-13,W.14)

tSection 1.6.41
Q. 5 Give any four advantages ofgear pumps.
[Section 1.6.6] (9r,r)
Q.6 Explain with skekh the workinA of variable
displacement vane pump. [Sectian 1.6.8] (W-fg)
Q.7 Explain axial pist n pump with neat sket h.
[Section 1.6.10] (9rr)
OR
Q. 7 What is the use of swash plate in axial plate in axial
pistoD pump ? /Spd'lon .1.6.J0l M-13)
OR
@f ,r, (rs"t.) 1-46 Basics ol Oil Hydraulic Systems

Q. ? Exptain working of axial piston pump u'ith neat

sLet h. [Sectiotu 1.6.10] (W'14)

Q.8 LiEt out any four criteiia for selection of hy&aulic

puop in hydraulic system. Erplai! eaah in brief.
lscction 1.6.14] ($12)
OR
Q.8 What are the selection ditaria for hydisulic puEps ?
tsectian 1.6.141 (W-11, W'fS)
Q.e Difrerentiate bctween gear puEP atrd piston pump otr
the basis of : fir.nctioD, coostructiotr, pre$ure ratrge
and Delivery ofoil.ISection I.6.I5J ($11)
Q. r0 Write the cause€ a.trd remedies for tbe followinS:
(i)Excessive heat iB oil
(ii) Noiry puBp
(iii) 16r, pressure in systemlSectioz -f.6.-l6l (W.14)

troo
Chapter

Hydraulic Valves,
Actuators & access

SyllEbus :

Valves I Construction, principle of working and symbols

of Pressure control valves - pressure relief valve -direct,
pilot operated , pressure reducing, pressure unloading,
Sequence valves, counter balancing. Direction control
valves - 2/2,3/2, 4/2,5/3,
Poppet valve, spool valve,
methods of actuation. Types of different center
positions. check valves, pilot operated check valves Flow
-
control valves pressure compensated, non pressure
compensated flow control valve,
Actuators : Classiflcation of actuators Construction,
working pranciple and symbols of Rotary Actuators -
Hydraulic moto6 Linear Actuators - Cylinders - single
acting, double acting, and their subtypes. Different
mounting methods.
Accessories I Construction, working principle and
symbols of Pipes, Hoses, Fittings, Oil filters, Seals and
gaskets, Accumulators
ffi ,." rrau-.) 2-2 Hydr, Valves, Actuators & access.

2.1 Control Valves

In hydraulic systems, we use "oil under pressure" to Perform
sp€cific tasks such as lifti[g, pressiDg, cutti]rg etc.
For doing t}le above said tasks, we have to control thee
important "work parameteG".
They arc
1. Amount offorce applied
2. Speed ofdoing the \r,orl
3. Direction of apphcation offorce.
For controlling the above Baid "work pammeteru', we have to
conhol thrce drffercnt "oil under pressure paraEetels"
They are
1. Prcsaure of oil
2. Rata of flow ofoil
3. Dircction offlow ofoil
For controlling the above said "oil under pressure
parameters', we use thrce differetrt 'control valves".
Pressure Conhol valve (PCV) controls the pressure of oil,
by which we can cotrtrol the force developed by the actuat r.
F = PxA
During extension,
and during rehaction, F =px(A-a)
Flow Control Valve GICV) controls the rate of flow of oil,
by which we can contlol the sp€ed of the actuator.
o
Dunng exteNioD. v = Ji
o
and during retmction. v = I-
Dir€ction Control Valve (DCY) cotrtlols the dir€ction of
flow ofoil, by which we can control the direction of motion of
the actuator.
Extension or retraction of cylinder, clockwise or anti
clockwise rotatiotr of motor are directly depend on direction
of flow of oil.
EEI (rssre) 2-3 Hydr. Valvss, Actuators & acc€ss
'.r
2.1.1 Classilication ol Conlrol valves
(a) Accordlng to functlon :
l. Prerruae coutlol valYes
. Reliefvalve . R€ducing valve
. UDloadingvalve . Couater balatrce valve
. Sequence valve
2. I)irection control velve.
. Checkvalve . Wvalve
. 3/2 valve . 112\ake
. 4/3 valve . 5y'2 valve
3. Flow confuol velve
. Fi:ed n€striction FCV
. Variablo Reltric-tion FCV
. FCV wittr R€verse Free Flol^,
. Pre6sure CoDpeDsatcd FCV
. Temperatur? CoDpeEst€d FCV
. Cam Op€rat2d FCV
(b) Accordln0 to the nrathod actuatlon :

l. Mrnual operrtGd
(a) Ps.lm operatcd
(b) Push button operated
(c) Hard lever opeBted
(d) Foot p€dal operat€d
(e) Cam (roller) operated
2. Pilot opersted
(a) Sitrgle pilot
G) Doubte pilot
3. Solenoid oporetod
(a) Sirgle solenoid
(b) Double solenoid
ffi ,." tr""t.t 24 Hydr. Valves, Aciualors & access

(c) Accordlng to conalruction :

1. Poppett?e: Ball t}?e, codcal poppet type

2, Spool type : Siding spool tlTe, rotary spool lype
3. Flow control : Gate valve, plug valve, needle valve,
poppet valve, buttcrfly valve et .

Valves and actuators are exactly similar for hydr:aulic

systems and pneumatic systems i]1 constmction and functioning.
Or y the difference is, hydmulic components are made
strongpr and hea!ry, they are Dade of steel, because, they have to
work under very high pressure of oil. Pneumatic compoDents are
made of lighter using alumiDum, plastic etc. because the pressure
of compressed air is just about 5 bar.

2.1.2 Factors to be Considered While Selecting

Control Valves :

Following factorc should be considered while selecting

control valves
1. Flow rat€ ofoil
2 Pessurc of oil
3. Force required by cylinder

4. Speed ofoperatioD ofcylinder

5. T}?e ofactuation oftbe valve

6. Port size
7. Space requirement

8. Temperature ofoil
9. Oil under pressure compatibility
10. EEvironmentalconditions
ffi,r" (r""r.) 2-5 Hydr. Valves, Aclualors & access.

2.1.3 Pressure Control Valves :

s.z)11

O. Slate ditteront types (any 4) of pressure conkol valves with

lheir

. Difrer€nt taskE demand clifrerent aDou.at of fotce. To lift a

chalk and tD lift a rock, the forces ate Dot the same.

. In hydraulic hachines, it isne@ssary to coDtrol the fone

genemtcd by the actuatoE (cylhder or motor).

. As we know, folte ofcylinder is the Foduct ofPie63urc ofoil

and arca ofpiston. F=PxA
. To vary the force, we need to vary any of these two, either
the pres6ule ofoil or th€ area of pistoD.
. lte si"€ of a cylinder is 6red; we can't have any kind of
valve to vary the size ofa cylinder.
. But we catr easily vary the pressure of oil by uaitrg a
pressurc cotrtrol valve.
. Pressur€ coDtrol valves are used to cotrtrol the Pressure ofoil
by which, we can contml the force developed by the hydiaulic
actuator,
ther€ aae vsrious types of pteseure coatml valves
. Pressure reliefvalve
. Pressure reduchg valve
. Counter balalce valve
. Unloading valve
. Sequence valve
@f userey 2-6 Hydr. Valv€s, Actuators & access.
'r"
2.1.3.1 Pressure Reliel Valve :

w-2012
Q. What is the funclion ot pressurc loliel valve? Wher€ it is
locat6d? Sketch direcl operating pressure Gtief valv€.
92014
O. With a n6at sketch, explain tho functioning of simpte pressu@
relie, valv€.
It's functioning is siBilar t t}te relief valve of a plessure
cooker of our kitchen.
If pressure inside the syst€m furcreases abov€ pre-set level,
this valve opens to release the oil bacL to tank, so that tlre
aystem pr€ssure comes to Dormal.

.E

B
d
e
E
\\l\\\\\\\\\r &
€
e

Spnnq
g

Fig.2.l.1
. Relief valve consists of an adusting screw, two supporting
plates on either side of the spring, and a conical popp€t
which arc mounted inside the valve bodv as shown in the
Fig.2.1.1.
. WheD the pressure at inlet increases above pre-set liDit, the
conical poppet moves inside against the spring force, and
creates a passage for oil t, flow to outl€t.
. The outlet of relief valve is connected tD the Frervoir in
hydraulic systems, so that oil flows to the reservoir tanh.
. Once the pressure comes to normal, the conical poppet sit
back in ils position on the seat, closes the passage from iDlet
to outlet.
ffi ,r" (^rsrt.) 2-7 Hydr. Valv€s, Actuators & accoss.

2.1.3.2 lmportance of Pressure Reliel valve :

O. Why p.essure reliet valv6 is essenlial for a itydraulic system ?

ID sny hydraulic syst€E, po6itrve displaceDent pump (PDP)

iB uBed atrd there will be linear actuatol€ (cylindeB).
Oil flows in to the cyli.trder during extension and rct action.
But wheo cylitrder completes it€ strote, piston is stoPPed, it
cadBot 6ove further, cylinder is fu[], oil ctDnot [o\r futo the
cylinder.
But, the pump is PDP; it won't see Fhether the cylinder is
full, whether there is any space for oil tD flow It simply
pumps oil.
EveD though there is no space for oil to 6ll i[ the cylinder,
the PDP keeps on punpinA the oil.
Oil coDing from pump does Dot 6trd atry space t fill, snd
hence the presaure will increaae,
A.s oil is iDcompr?ssible, this incrase iD Pre$trlc is very
rapid. Withia fraction of a second, compotrents of the sy8tem
will burst ald oil cohes out (if ttrere is Do pressure relief
valve itr tie ciruit).
Usually, low strength component€ such 6.s seals, pressure
8auge, thiD pipe, defective pipe et . will ruPture at weaker

Every time ends up its stroke, there will be rise

tie cytidder
in pressue to burst the system component€
And hydraulic cyli.trders are U.sed to extend and rctract
coatinuously as we br€athe.
Hence, pressure relief valve is very importatrt, and it should
b€ set for a pressure well below buxt preasure of weakest
component.
Pressure relief va.lve releas€ the o to flow back to reservot
every time the system pressure crosses the pre-set value due
to coDpletioB of strokes of the cylinder.
Thus pressure rclief vslve safeguards the syst€m
coBponeots against dsmage.
]ff,." MSBTE) 2-A r. Valves, Aclualors & access

2.'1.3.3 Pressure Reducing Valve:

*dtt1
o. Draw and explain working of pressurg aeducing valvo.
w-fr11
Explain wlth neal sketch worklng of directly opeaated p.sssuao

1
=
Spring

Fis. ar.2
Pressure reducing valve is used to maintain constant
reduced pr€ssure in the syst€m. It haB an adjusting screw, a
sprhg, a conical poppet fitted to a diaphragE a-s shown in
the Fig. 2.1.2.
If the pressure at outlet 'O' increases, tlle diaphragD defecta
upwards, due to which, the conical poppet vrill also move
upl/aids t close the passage of oil llow. Thut the flow
reduces aDd the pressur€ rcduces to normal.
Once the prBsur€ comes to trormal, the diaphragm deflects
downwards and the conical popp€t moves downwards and it
opens the passage for oil to llow.
This valve is caled 'rcducing valve" ill hydraulic syst€ms,
and pressure regulatot' in pneumatic systems.
ffi 2-9 Hydr. valves, Actuators & accsss.

2.1.3.4 Compalison between Reliel Valve and Reduclng

Valve :

w-2011
O. Give lhe comparison between pressure reliel valve and
pressure reducing valve.
w-2011
O. Ditlerenlial€ between prcssure reliel valve and pressure
roducing valve with respo6't lo its lunction symbol, normal
position ard oPerated element.

E E

fig.2.rj
Sr.. Pressul.e Relief vetve P*ersurc RedueiDg Valve
No.
I T'his is NC (Normally This is NO (Normally Open)
Cloeed) type vl.lve
2 Fitted in by-pa.ss tiae to Fitted h oain line to
rcs€rvoir tsak. system.
3. Outlet is connected to Outlet is connected to
reservot ta-nl.
4. Inlet pre$ure is system Outlet pre$ure is system
pr€saune.
5. lnlet Fessure is tie pilot Outlet pressute is pilot

(; It op€D6 shen inlet It closes when outlet

plessur€ (3]Btem pre$ure pre$ure (system plessure or
or pilot pr€ssuie) bec\omes pilot pressure) becomes more
more than preset value. than preset value-
@re tv 2-10 Valv6s, Actuatorc & ac-c6ss.

Preslure ]lllet valv! ls normllly closod, uhy?

. R€fe! Fia. 2.1.3.

o PreseuE relief valve is fitt€d in the "by-pa.ss line, teadirg

towards oil reservoir.

. Ifthi8 valve is opea in it6 oormal position, ttren the oil

punped by the pump will flow bsck to the reservot, and
syst D will not get oil.
. Hetrce this valve is clos€d in its nornal position. It i.s
NC(oormally closedhype valve.

. It op€Ds only when tle sr€t€D prcssule caosses the pre-set

limit t release the oil t, flow back to reservoir.

PreaauE r.duclng valve ls nomally op€n, why?

. R€fer Fig. 2.1.3.

. I,reseure r€ducitrg valve is fitted in the "main line" leadiag

towardB the sJ,st€D.

. lf this v6lve is clos€d in its Dormal position, then oil can not
flow though it, ard the systan EiIl not get oil.
. Heac\e this valve should be oped ilr its Dormal positioD. It is a
NO (trormally opetr) type valve.

. It cl$es ooly when the system pressrr.re hcresses above ltre

pre-set value, and it opens sutomatica.lly oDce the pressure
come6 to normal,
ffi IFP (MSBTE) 2-11 Hyd r Valves. Aclualors & access

2.1.3.5 UnloadingValvs:
. Beforc going int! tn€ topic "unloading valve", one should
undeEtand "idle period" of anv hy&aulic sFtem'
. Idle Friod i6 thst time duration during v'brch, tlte a€tuators
(cylinders of motor) 6re idle, that is they rchain stationaiy
in either extended position or rctracted position'
. ldle p€riod is trec8sary for l@ding and unloadhg (the worL-
piece in case of machine tools).
. ldle period is very larSp comPsred t actual working Priod,
extension tskes a second and retraction happenE wit}ti[ a
secoDd. But loading and unloaditrS tskes considemble
amount of time, s.trd it ca-n be Einimized t some ext€Dt by
Proper automation.
. Durina this idle period, the purnP is running and con8uming
power, but the oil flows continuously back to the r$ervoir
(because it canEot go to the actuator which is ide) thrcugh
the relief valve at high pressure Gecruse the r€lief valve is
set for high plessure, it opens only if high presBure is
reached).
. Power coDsumption durin8 idte p€riod is sbsolutaly a
big los3. Becaue, tiere is no any output oechanical work'
I'he energy given to pump during idle period Sets convertcd
into heat eDergy and causes over heating of the hydraulic oil'
. ContiDuous flow of larae qutltity of high pressure oil
back to the rcservoir duriog idle period, through the s6all
opening of prcssur€ relief velve causes pover lose and
overheating of oil.
Power consumptioo (watt) ratE of flow (m3/s) x pressure
=
(N/6 :))

To avoid thiB power losa and overheati.og of oil, unloading

valve ie us€d.
Whenever the system is idle, udoading valve lelesses the oil
bsck to reservoir at less pnessune, so that, over heatiDs of oil
a[d power losB is svoided.
ffi IFP (MSBTE 2-12 Hydr. Valv6s, Actuators & access.

Construction ot unloading valve :

E
I
j]ol
I rl$ \Nl\Nt I

Sp.ing

FiE 2.lA
. Unloading valve consists of sn aduiting snew, a spring
loaded conical poppet as shown in Fig. 2.1.4.
. Unloading valve is set for less pressur€.
. When the pilot pressure iDcreases above this preset
pressure, the conical poppet will be liftcd off from its
seat
and opens the connection from inlet to outlet.
. Thu!, oil flows from the pump to rcservoir at less pressure,
and hence it saves power atrd avoids over heating of;il.

2,1.3.6 Comparlson between Rollof Valvo and Unloading

Valve :

E
n
,6
jE
r6

l'is.2.l.s
Eff,', MSBTE) 2-13 Hydr Valves, Aclualo6 & access

Slmllaritles I

. hlet is coDnect€d to
PunP.
. OuU€t is coDnectcd to oil .eservoir.
. Both are NC (Normally ctosed) tvpe valves'
. BotI have 'sprirgl loaded poppet" which sits firmlv on t}le

. Both have "adiustable screr't s€t the sPring tetrsioo,

aDil hence to sdust the piesaure at which the valve
should open.
Dlrl?rEncqB :

Sr. Plessure relief valve Unloading valve

No.

I Its iDlet itself is its Pilot It has a separate Pilot

con[ection.

2. It is r€t for malitnum Itfor the Dinimum

is set
pr€ssuE rcquired for preasrre required during
operation of the systeE. idle p€riod olthe syst€m.

3 It its inlet
opens when It opeos *'hen the Pilot
pressure (maximum systeE pressure (minirnun idle'
pressure) incrcases above period pressure) increaEes
above prcset value.

It is a safety valve which It avoids ovei heating of oil,

avoids damage to the sEd
system components due to It aaves l,ower to a 8r€ater
high pressure. exteBt.

Unloaaling valve saves Iot of power, and it avoids overheating

of oil
Nole: Beler Section 3.2,l lor circuil using unloading valve' and
numerical showi its tn
 @,r" (u""-. 2-14 Vafues, Actuators & acc€ss.

2.1.3.7 Counter Batance Valve :

. The counter balance valve is used to 6eate holdhg pressuie
in the cylinder, in order to prevetrt fallitrg of the load while
descending.

SPnng

Fiz- 2.t.6
. ID other words, it is used to pr€vent over n oning loads
(negative loads or ruIl-arvay loads).

Construction :

. Count€r balance valve siEilar to the pressure lelief valve ilr

construction. But, it has a check valve for reverse fre€ flow.
. Counter balance valve is shown in Fig. 2.1.6.
. It has a spring-loaded conical poppet, which is closing the
inlet, not allowing oil under pressure tD llow throwh it.
. It op€Ds only whetr the pEssure iD the cylinder b€comes
more than the preset spring t€nsion.
. The spriog t€nsion is adjust€d by turntutg adjusting scr€w.
. The counter pressure should be adjusted for a value more
than load-induced pressure (Approximat€ly l.A tiEes).
. Iaad itrduced pressure (LIp) is ratio of "load" to "ar€a of
piston".
Nole : Refer soctlon 3.22 for circuil counter balance valve
ffi MS 2-15 Hydr valv6s, Aclualorc & access.

2,1.3.8 Sequence Vslvs :

. A sequetrce valve is uEed to perform two opeEtions in
seque;ce one aft€r the other. For exaaple frst cylinder_l
will exteod and after that cvlinder-2 will extend'
. It has an aqjusting screw, a spriDg end a codcal poppet'
which arc, mouDted i[side the valve My as ehowo in
Fis.2.1.7(a).

SpnnS

2
2

Flg 2-l,(.'l
. It has oDe inlet port ard two outlet ports, outlet Port "1" aod
outlet port "2'.
. lvhen oil under pressure is supplied to inlet port of sequeBce
vaive. it flows directly to outlei port "1' Hence, firgt cylioder
exteDds.
. Bv mmoletioa of exttnsioD of first cylinder. preseure io the
lle increases and henc€ tbe poppet of sequence valve lift_s ofr
froE its seat gnd atlows oil to flow to port 2", hence
cylinder2 ert€nds
. ibos, s€qrrencing is achieved between the two cylindets'
. Seouence ,alve can allow oil io rever€e directioD Fom po
iii grt it does not allow reverse flow froE port "2"
Retraction of first cylinder is poasible, but rehactioE of
second cylinder is not Possible
Hence, a check valve is essential for revers€ free flov, oI oil
from cylinder-2 to taDk. for tetraction of secotrd cylinder
Noto l Ggnerally s€quenco 3.12 valves come with integ'al check
valve as shown in 2.1
 ffi,r, (u"rr.r 2-16 Hydr Valves, Aclualors & accass

I--
I
2

Fis.2.l.7(b)
Nole Reler section 3.12 tor hydraulic cjrcuits using s€quencing

2.1,3,9 PressureSwitch :
. It is sn electrical ss.it h, which is operatcd due to pressurc of
Iluid. When oil under pressure pressure exceeds the preset
value, this swit{h breaks the electrical contact with electric
motor, so the motor is tripped ofr. Thu.s the pump stops.
. Pressure switrh is a safety device; it avoids ilevelopment of
over pressure and prevents the chances of accidents.
2.1.3.10 Hydrautic Fuse :
. Hydraulic firse is safety device used to avoid development of
of pressure. A very common exaeple is the fuse of
excess
pressure cooker. It is a disL with a tbrough hole at its center.
This hole is blocked by pre-stressed lead.
r If the system pressure increE.ses beyond certain limit, the
fuse raptues, allowing the oil under pr€ssure to flow out.
Thus the system components are protected.
. Once the fuse is broken, the whole set_up will becoBe out of
service until the root cause for high pressure is truced-out
and rectifed. Only afier solving the actual pmblem in the
aystea, a trew fuse should be 6ttcd aod tben oaly, the
machine should b€ staited.
ffi,." MSBIE) 2-17 Hydr. Valves, Actuators & accsss

2.1.4 Direction Control valves I

w-ml1
vaive with
o. Give tho classifi:ation ot D.C. (Direcrion Conlrol)
respoct to lollowing points :
(i) Valv6 elsment used in constnElion
(ii) Number ol Ports and Posilions
(iiu Methods of acluatiorvoPeration.
Dircction control valves are used to conhol the direction of
of
flow of fluid, thereby to control the direction of movement

For extension or rehaction of cylinder and for clockwise or

,"ii"i*f.*i"" rotation of 6otor, we need to change the
iiJio" of no* of lud, which is done by direction contrcl

Classilicatlon ol dlroction conlrol valves :

A) Accordilg t,o the method actuation :

1. Maaual oPerated
(a) PalE operatcd
(b) Pueh button oPerated
(c) Hand lever op€rated
(d) Fmt Pedal oPerated
(e) Cam (roller) operated
2. Pilot operat€d
(a) SiaglePilot G) Double Pilot
3. Solenoid oPerat€d
(a) Single solenoid (b) Double solemid

B) According to tYP. olsPool:

. Poppet tyPe
. SlidinS sPoot tYPe
. Rotrry spool tYPe
C) According to nuEber of t'orts rld lrositiont :
Ctlech,va]ve, W,3n' 42' 43' 5D etx-
Eff,r" (r.rr. 2-1A Hydr. Vatvos, Acluators & accoss

2.1.4.1 Check Valve

s-2012
o. Erplain wo*ino of directy operaled check valve with ne6t
sketch.
w.20r3
o. State lhe tunctaon ol check valve in raulic circuir
Check valve is a uni-directional v3lve (rcn_return valve),
which allows oil to flov{ in only one direction. It will not allow
oil in other direction. Fig. 2.1.8 shows a check valve. It has a
springJoaded ball or conical poppet inside the valve housing.
When oil under pressure is
supplied to port-A, the oil
exerts pressure on the ball
agaimt the spring force;
hence the ball will be lifted a
off ftom it€ seat, aad crcrtes
a pa$age for oil to flow.
Hence oil can llow from porL
A to port-B.
When oil under pr€ssure i_s

supplied in opposite
direction, liat is, t port-B,
the oil forces the ball to Bit
firmly in its seat; heace the
passage is cloaed by ball. the
oil csDnot flow frorn port-B tD Fie.2.l.8
port-4.
Check valve is atr importsnt vatve, which finds applicetion
itr
many circuitr for obt,ihing rreverse fi€e flow. In oae
direction, oil under pressure has to flow timugh flow
cotrtml
valve, sequence valve et . and in the other dircction
it should
be free flow. Io such case, e check valve i_s coDDected
parauel
to the main velve
@F,', 2-19 Hydr. Valves,

2.1.4.2 2l'l, Dlrr,dlai Control vdw :

ltis valYe has tso ports and tso Po€itioDs of sPool lhe two
ports sre inlet port-A aod outlet port_B'

Slldlng lpool tYPe 212 DCV :

. The Fig. 2.1.9 showa a slidiag spool sPri!8 rctum tvpe
NorEalty Closed Z2DCV.
. In normal position of the spool, the ports are ctosed; oil
cannot flow ftoD Port_A to Port-B
Whett the palm buttoD i6 press€d, sPool moves to oPeD
. the
port
passege froD port_A to port-B, and hence oil flol^'s ftoD
A to Port B

t tiI

-
Fig.2.l,9
 2-20

Rotary spool type 2/2 DCV :

s-2013
o. the o,

The Fig. 2.1.10 shows a rctary spool t ,pe ?2DCV.

In first position of the spool, the ports are closed; oil ca.Dnot
flow froh port-A to port-B

Whea the spool is mtated tbmugh 9Oo, it opens the passage

from port-A to po!t-B, and hence oil flows ftom port A
to
port B.

l
I
Fis.2.l.l0
 FP (MSBTE) 2-21 H r Valves. Actuatoxs & access.

2.'t.4.3 3/2 Direction Control Valve:

s-2012
woridng'
O. Oraw a nsat sketch of 3f2 D.C valve Explaln ils
w-2013
O. Draw skotch ol3 x 2 DC pneutrlatk valvo, explain ils working
s-2014
Sketch th€ two posltlons of sliding spool type 32
DCV and
o.
in briel

This valve is used to operate siagle acting cylinderS'

Ithas thre€ Pork nsmety, PuEp port or idet Port "P''
Cylhder port "Al and Tank Port'I"'

3/2 llldlng spool valve :

retum
. The Fig. 2.1.11 sho*s palm buttotr opelated spr,ng
t1ae Vi suaing spool valve lt has a spring-loaded
sPool
t'T€ of
ioiia" tt" ,"t* uav. In frgure, it is palm-operated

. 3/2 va.Ives ar€ used to operate siDSle actiDg

cylinders and
unidirectional 6otor3.
. ln spoot position as show! iD Fi8 2111(s)' there purnp
i3
to
cotrnectiotr from port'P to port'A Oil llows
ftom
single sctriS cyiinder. Hence, the eingle acting cylinder
extends. The tshL, Port_T is closed'
. ln spool PositioD as shown in Fig 2111(b)' the& is

coDnechon from port-A to Port_T Oil flows

Eom single actinA
cylioder to tank. Heoce the single acting cylilder
rctrac'ta

Ttre iBlet Port Port-P is closed'

 191 rp 2-22 Valv6s, Actuators & access.

T
(.)

PT
(b)
Fig.2.l.lr
312 rotary spool valve :
. 2.1.12 shows a.t/Z rcta.ry spool vatve. h has rorary
T",ap
spoot. inside the valve body. The spool is rokted though
lZUo to op€rate tle va]ve.
. In spool position as shown in Fig. 2.1.12(a), tnere is
coD_necdonfroE p to A. Oil uoder preseure flo*" fro_ o,r-o
to sugte actiDg rylioder. HeDce the cylinder ertenas. nre
taDl<, port-T is closed.
. Wlen rhe spool js tumed to 1200. as shown in showE in Fig.
2.1.12(b). thele is connection &om port_A to port.T.
Oil flows
rrom single acting cyliDder to ta_o}. Hence rhe cyliDder
rehacts. I'he inlet port port-p is closed.

T
T
(') o)
Fi& 2.1.12
lg tFP MSBTE) 2-23 Hyd r valves. Aduatorc & access.

2.1.4.4 412 Oi[eclion Control valve

92011
o. Draw a sketch of normal and actuated positions of 4/2 DCV
s.2014
o. Sketch the two positions ot rotary spool typ3 4/2 DCV and
in brief

This valYe is used to operate double actiDg cylinders and bi

di€ctioaa.l Dotolts
It ha6 four ports naDely, PuDp port or inlet port "P''
Cylinder Port "A:'
CYtinder Port S" and
Taak Port 'I-
B

4f2 .lldlng spool valvo :

. trle Fig. 2.1 13 shows spring returtr type sliditrS sPool valve
It has a spring-toaded spool inside the valve body ln
Fi8. 2.1.13, it is palm-operated t1'pe ofvalve'
. ln sPool position as showo iD Fi8 2113(a)' therc is
coDnec'tion from P to A and B to T. Oil fiows to cap eDd port
of rylinder, anal comes out from md end port Hence the
double acting cylinder extendB.
. When the palm button is pressed, the spool position fu ag
shown itr Fig 2.1.13(b), ther€ is coDnection from P t'o B and
A to T. Oil flows to tod end port of cylinder, and @mes out
fioD csp enal port Hence the double acting cylinder tetracts'
 MSAIE) 2-24 Hydr. Valves, Aciuators & access.

(b)
II& 4r.13
ilE rota.y lpool valvr :
. The lig. 2.1.14 sholrs a 42 rotsrJ. spool valve. It has Dtary
spool i-D-side the vatve body. The spool ia rotated tbmugh
90o
to operat€ the vslve.

(.) (b)
Ftg.2.t.t4
In spool Fosition as showd in Fic.2.1.14(a). there i!
connecrion fiom P to A atrd B to T. OiI flotgs to csp edd
of cylinder, and comes out from md end port. ilence'ttre lDrt
double acting cyliDder extcnd_s.
WheD the spool is rct"Et€d tbftugh goo as shovrD itr
!ig. 2.1.14(b), tlpre is coD.EectioD frorD p to B ar)d A to
T. Oil
flows iod end port of cylinder, and comes out froD cap etrd
.to
port. Hence t}le double actirg cylitrder retrscts.
 2-25 r. valves. Aclualo6 & acl€ss.

2.1.4.5 43 Direction Control Valve:

s.201,
O. Explain 4 way 3 position direclion control valve used in
ic with sketch
I'his valve is used to oP€mte double acting cylinder and
bidir€ctional motor.
It has four ports namely, PumP port or itrlet Port'P',
Cylindet Port "A'
Cylinder Port "B" and
TatrL Port -I-'
. It ha6 thi€e positioDs ofits spool.
. In fitst position, there is connection from P to A and B to T,
hence cylinder/motor hoves in oDe dir€ction'
. In the other Position ofspool' there is connection from P to B
and A to f; hence tfie cylinder/motor runs iD opposite
direction.
. In the oiddte position of spool, the cytitrder or motor stoPs, it
E'ill not move in any di.rectioo
Symbol ol 4/3 DCV :
AB
L
operated
I[:PT Detent
tyPe
Closed cenlre

4f! rlldlng .Pool valve :

. ln first positiotr of spool Position as shown in
Fia. 2.1.15(;), ther€ is connectioa ion P to A and B ta T' Oil
flJwe to cap end port of cylinder, and comes out fron rod end
port. HeDce the double acting cylinder ext€nds'
APBT

Fis.2.l.l5(a)
 MSB 2-26 Hydr. Valves, Actuatols & accsss_

Itr s€cond positioD of spool positiol as shown id

Fig. 2.1.15(b), there is connection from p to B and A to T.
Oil
flows to rod eod port ofcylioder, anil comes out froD csp
etrd
port. Hence the double sctiug cylinder rehact€.

Iis.2.l.t5(b)
Wben the spool is kept in the middle position as snown
in
the Fig. 2.1.15(c). all ports ar€ closed, and hence the actuaror
stops.

Fie.2.l.ls(c)
. This is closed centre mid position.
4E rotary spoot vatve (ctosed centre mid-posnlon) :
FiEt ard second positions of T
spool are as explaioed iD ,U2
rotary valve.
Middle position is shown iD
Fig. 2.1.16, all polts are closed, B

and hetrc€ the achrator stopo.

This is closed centre roid
positioD.

Fig.2.l.16
m,r"r"""r., .-r, ,
Dlfterent mld.poaltions ol /y3 DCV :

Sr. Name S)'mbol Erplanation

No.
1 Open center All ports are cotrnected to ta[k.
tTe This valve is good to use if there
is no negative load.

2. Closed center II All pork are clGed, this valve is

tvpe -r -r us€tu1 in holding the falling load.
But it is not us€tul iD avoidiDg
over heating ofoil

3 Tandem _t -! Cylinder ports A aod B are

cent€r t]?e |--l clos€d, heDce it can hold the
falliDg load.
Pump port P is open to taDk port
T, hence it avoiils over-heatiag of
oil and saves power
I Regenerative Pump port P, cylinder port A and
centre type cylitrder port B all arc connected .
TaDk port T is closed. This valve
is used in Regenerative c cuits
5. Float t}?e Both A aDd B ports arc open to
tank port T. Pump port P is
closed.
6. Other t],pes

I
L__l
'r -r _r
EEf,r, (rs"r.) 2-28 Hydr. Valves, Actuators & acc€ss.

2.1.4.6 5/2 Direction Control Valve

5/2 DCV is used to operat€ double acting cylindeE.

It has five ports lamely, Pudp port ?',
Cylinder ports "A" and "B",
TanL ports 'T1" and 'I2".
AB

\
T1 PT2
512 sliding epool valyo :
. The fig. 2.1.17 shows spring rctum t)?e sliding spoot valve.
It has a spritrg-loaded slrool inside the valve body. ID fi8ure,
it is palm button operated spring return type of valve.
. ln spool position as shown in Fig. 2.1.1?(a), tierc is
connection froo P to A and B to T2. Oil flows to cap eod port
of cylinder, and comes out from rod end port. Hence the
double actiag cylinder extends
AB

I
T1 Pf2
Fig.2.l.l?(a)
When the palm button is piessed, the spool position is as
Bhown in Fig. 2.1.17(b), there is coDnection from P to B and
A to T1. Oil flows to rod eDd port of cyliDder, and comes out
from cap end port- Hence the double acting cylinder rctracts.
AB

T1 P12
ris.2.1.17(b)
W IFP (MSBTE) 2-29 Hydr. Valvos. Aclualors & access

5f2 rotary spool valv€ :

It hes mtary spool i$ide tlre valve body. The spool is rotst€d
tbrowh 72't opeEte the valve.

T1
T1
12
I2

B B

Fig.2.l.lE

*2014
O. Explain \rhy M OCV is prelerred lor hydraulic syglems and
5/2 DCV malic
The purpose of 42 \alve aod V2 valve is same, that is, to
operate double acting cylinder.
For hydraulic eyatcEs,
. 4/2 valve is preferred. Because, it has only one tsnk port,
oflly one return pipe line is sumcient per valve.
. Y2 valve h aot prcferred. Because, it has two tsnk ports, two
retum pipes are Equired per valve.
For paeumatic systeEs,
PEeumatic syst€ns does not need retum lines, air is
exhausted to atmosphere at the exhawt port of the velve
itself.
5/2 valve b preferr€d. Because, its coNtructiotr is siDpter
thetr tU2 valve (i!ca-s€ of slidiry spool type). Hence, less cost.
ffi ,r" (r."r.) 2-T Hydr, Valvos, Actuato6 & access.

2.1.4.7 Methods of Actuation ol DCV :

Direction coDtrol valves are us€d to control the direction of

flow of fluid, by which, we can cont ol the directioD of EotioD
of actuator.
By shifiing the spool po6itioD of DCv, we can obtain either
exteflsion or ret actioD of cylinder, aDd clockwise or counter-
clockwise rotatioD of Eotor.
The spool of DCV can be shifted by Beveml ways. Some
rtant methods are given below

Lever operated

Palm button
-l__n
Manual
operated __,Hl
1

l=
operation
Push button
opemted

-il
Foot pedal
operated H
2
Solenoid
operation
Sinsle solenoid
F
Double solemid
{}

3 Pilot operation
Single pilot
F
Double pilot
{}
EEl,r, tr.rt.r 2"31 Hydr. Valves, Acluatorc & acc6ss.

2.1.5 Flow Control Valves:

s-2011
O. What is flow contaolvafue?
. f'bw cootrol valve is used to co rol the rata offlow of fluid,
by which, we can control the speed oftbe actuator.
. If flow rate of oil tu moie, then cylitrder will frll quiclly and
hence the piston will hove faster.
r If flow rat€ of oil is leae, then cylinder will be frlled slowty
snd hence the pi.ston DoYes slo\rly.
. Speed of the actuot r is proportional t, the rata of flow.
Hence controlling the llow controls the speed of actuator.
this is achieved by llow cotrtrol valves.
. Therc arc various t T€s offlow cotrtrol va.lves (FC9.
o Fired Regtriction FCV
o Variable Reskiction FCV
o FCV witlt Beverse fYee Flow
o Pressure CompeDsatcd FCV
o Temperature CompeDsatcd FCV
o Cam Opented FCV

2.1.5.1 Flxod ResHctlon FCV:

This is not a valve; it is simply a restrictior! with a small

openiog (orfice). Whea fitted in the system, the oil has to flow
through this small hole. I'his reduces the flow late of fluid. But it
does Dot have any Eeans to vary the flow rat€ or to vary the area
offlow.
Symlol .
ffi,r" lrsar.y 2-32 Hydr. Valves, Aclualors & access.

2.1.5.2 Varlable Reslliction FCV :

*20r 1
Q, Explain non pressure compensaled llow control valve.

This valve has a hand wheel or knob, by turniag which, we

can change the ar€a offlow, a.od thus we can change the rate
offlow ofoil.
Ordinary water tap is a bettDr example for understandi[g
the tunctionirg.

There are maay t,?es and many desig s, examples arc

leedle valve, gate valve, ball valve, butterfly valve,
diaphragm valve, poppet valve, etc.

TI IT

r\
\J/

Fig.2.1.19

Fig. 2.1.19 shows a needle valve. It has a needle, which

moves up & down by turning the sclew- This alters the
pa.ssage for oil to flow, which intem alt€rs the rate offlow.
@,rp 2- Hydr. Valv6s, Actuators & acc€ss.

2.1,5.3 FCV wilh Reverse Free Flow

Spa.g

<F
+
fi& 2.r:O
this valve is u.sedto control the flow late in one direction
oDly. In the otler dircction, the flow is not coDtrolled, i.e. it is
free flow.
By this, we can have contmlled spe€d of actuator io one
dircctioD alrd unconholled speed ilr tile reverE€ direction.
By this slow forward stroke and quicL return of cytidder is
postible.
Such quick rcturn Eotion is required in machines like
shapers, planels, slottiog Eachine etc.
Fig. 2.1.20 shows a flow control valve with reveme free flow.
By tuining the screw, we can move the needle up and down
to vary the passage for oil rlow.
flhe needle has a drilled hole in which, spring loaded bau is
mount€d. This is check valve, aDd it allolys oil to flow
through it in otre direction only.
From port-B to port-A it is free llow thmugh the check valve;
there is no control over the flow.
trYoo port-A to port-B, the flow is tbmugh the passage
cleat€d by the needle, this is contmlled flow.
@ ,r, (r""rr) 2-34 Hydr, Valves, Acluators & access

2.1.5.4 Pressure and Temperature Compensated FCV :

w-2t t2
O. What is pressure comp€nsal€d flow coatrol valve? How does
pressure componsaiion takes place.
w-2t11, w-m13
O. Explain pressure compensaled flow control valve with neal
sketch.
w-ml1
O. Explain the wofting of pressure comp€nsated llow contaol
valve lsed in raulic
To coatml the mte of flow ofoil, we use flow control valve. By
op€ning the flow contml valve, we can inclea-se the llow of
oil. And by closing it, we can reduce the flow.
we car keep the valve opening for a required flow rat€.
But, flow rate does not remain constant. It gets affectcd by
the chaoges in prcssure and temperature of oil.
IfiDlet prcssure is more, then there will be increase i-n llow.
lf outlet pressure is more, then there will be reductroo in
flow.
If temperature of oil is more, thetr due to decreaae in
viscosity, there will be hcrease i-n flow rate.
So, in orde, to maintair constant flow rate,
"Any change in flow rute which happens due to changes in
pressure and temperaturc should be corrected
(compensat€d)".
And tlis is done by the coErpensatioD mechanism oI the

2
, t \-1,/
1 T
I4"-L
a 1 - Press!.. snsitjv6 spool
2 - Thomd s6nsiiiv€ el€monl

lig.2.l.2l
lZFl,.",u""r., 2-35 Hydr. Valvss, Acluaiors & access.

. The valve ha6 e pressurc sensitive spool snd s temperatue

setrsitive element mounted inside the valve My aa shown in
the fig. 2.1.21.
Prearure compsnaatlon :
. lf inlet pressure (Pi) increases, then rats of flow will
To compensate this, in the mecha.dsm, inlet pressure acts on
the spool from the top, and the spool moves down. Thus, the
area of florv reduces and the flow reduces to normal.
. If outlet pressure (Po) iDcreases, then rat€ of Oow will
decreage.
To comp€nsate thi6, iD the mecbaniEm, outlet pressure acts
on the spool ftom bottom, and the spool moves up. Thus, the
ar€a offlow increases and the flow comes to normal.
Temperature compensalion :
. If temperature (T) of orl increases, then naturally its
viscosity will reduce, and hence rate of flow will increase.
To compensate this, in the mechanism there iE a
"temperaturc sensitive element". It has high thermal
expan6ion; it expands due to rise in temperature and reduces
the passage for oil to flow. Hence the flow comes to normal.

2.1.5.5 Cam Operaled FCV with lntegral Check

Valve (Deceleration Valve) :

II the cylinder is long, that is, if stroke length is more and

the speed is high, then naturally, the pistotr-impact on end-
covers is considerably high. Continuous hsmmering of piston
oD these cover-plates causes loosening of tie rods ard leakage
offluid. Also it will damage th€ cover plates. Hence to avoid
sudden impact of piston on the cover plates, cushioning
c cuit6 are used.
Cushioning means "reducing the speed of piston at the end of
the stroke". That is, making the piston to eDd-up its stroke
slowly. For this purpose, special t ?e ofFCV is used which is
known as cushioning valve or deceleratiou vs]ve.
Actually it is a Cam Operated FCV crith integral chect
vaIve.
m IFP (MSBTE) 2- Hydr Valves. Aclualors & access.

Ithas a roller, which is op€rat€d by any

moving pait ofthe machiDe.

In normal position, it has free flow. When

the roller is preased by any movhg part of
the machine, the llow gers reduced as it
flows througb the FCV. By this, the
?
machine table, which waE fast earlier, is
hade to complete its stroke slovrly.

It has a check valve for leverse free flow. Check valve is

required because, the small coDtrolled flow tbrough FCV
alone cannot iDitiate the rctum stroke of the cvlinder-

t!
-

(a) o) (c)
FIE LI-22

Oil is llowing in ,oMard Once lhe machine labls Duing relum stroke of
darection to cylinder Press€s lhe roll6r ol 2/2 cylind€r, oal is allowed
through 2/2 valve, valve, oil slads llowing to tlow lrs€ly lhrough
h€ncs machin€ labl€ is through FCV. Hence the chsck valve, retum
moving in ,ofterd speed ol cylinder and slrok€ stans with hagh
direclion with high machine table rduces. speed.
sp€ed.
EEI ,tt (r"ttut 2-37 Hydr. Valves, ActuatoG & accsss

2.1.6 Special Type Valves :

2.1.6.1 Time Delay Valve:

w-2011
o. wilh neal skelch the of lim€

Thfu valve i6 used to have required amount of time delay

between two opentions. For example a cylinder extend.s 6rst
and it rctmcts automatically after pr€set amount oI time.
Fig. 2.1-23 shows a time delay valve. It ha.s an in-built
reservoir, flow control, a check valve, aDd pilot operat€d 3/2
direction contml valwe.

T
1

Fig,2.1.23
When the oil under pEssure is admitted through inlet port
of this valve, it llou,s thrcugh check valve fills in the
chamber, and exerts force on the spool. Due to this, the spool
iE pressed against the spring force, mskhg the connection
from port-P to port-C. The cylinder extends.
When inlet prt is open to oil reservoir, oil flows through flow
control valve slowty back to the Eservoir. Pressure in
chamber reduces slo*ly. Once the pressure trecomes less
than the spring force, the spool shilts back to make the
coDrection between port-C to port-T, cylioder rchacts.
Note : Beler sectlon 3.27 for lime circuit.
ffi ,r, (r""r.) 2-38 Hydr. Valves, Actuators E access.

2.1.6.2 Shuttle Valve:

A shuttle valve is shown in Fig. 2.1.24.
It has t{,o inlet porta, A and B ad one outlet port C.
It corl3ists of a ball or poppet inside the valve body.
When oil under pressurc is supplied tD any of the two inlet
ports, inlet port A o, inlet port B, the ball-poppet closes the
other inlet port and oil under preBsur€ llows to cylinder port
C.

"l

(r)

"l

Fig- 2-l.A
Truth Tsblc

Input A Input B C
Yes

Yes Yes
No
Nole : Beler secllon 3.24 for hydraulic shuttle valve circuit
l4l rFP ( MSBTE) 2-39 Hydr. Valves, Aclualors & access.

2.1.6.3 Twln Prossurs valve :

A tvrin pressure valve is shown in Fig. 2.1.25.

It has h{o inlet ports, A and B and one outlet port C.
this valve has AND logic firnction.
AND logic functioD stat meflt is "'when both of input eignals
arc presetrt, theo oDly there will be output sigDal".
Thie valve consists of a spoot inside the valve My. when oil
under pressure b supplied from ooly one iDlet port, the spool clos€s
the outlet. If oil uDder pressure is supplied from both of inlet pork'
then only the outlet port open8.
AND logic ir used i[ ssfety circuit 'two hand oPeration of
press'where, the prees operator has to eDgage both of his haDds t,
start or operat€ the presa, thereby; his handE viill be protected
froE sccident (as he don't have any tiird hatrd to be left below the
punch).
c

Truth l ablc I B

Input Input Output

B C (,)
Yes
c
Yes No
No Yes No
No No No

(b)

I I a

(c)
-
Fis.2.1.25
Note : Refer section 3.25 for valve circuil.
llEl rFp (MsBrE) 2-44 Hydr. Valves, Actuatols & access.

2,1.5.4 Pilot Operated Check Valve

*n)13
O. Explain with neat sketch, construclion ol pilot operated check

O. Explain opposing load and over running load consjdering the

case ol and lowerin the
A normal checL valve has only two ports, ngmely inlet port
"A" and outlet port "B".
Normal check valve is open in forward diEction. and closed
itr the rever€e direction.
Where as, a pilot operated check valve has aa additional port
cslled pilot polt "P".
By the application of "pilot Fessure" through the pilot port
?', the check valve which was closed is made to open, or the check
vslve which was open is made to close.
Accodingly, there sre two twes of "pitot operat€d check

I'hey are, 1. Pilot-to-open check valve and

2. Pilot-to.close check valve.
Both are discussed in parallel for better comparison between theh.

Pilot to-open checL Pilot-to.cloee checl

valve valve
Symbol
B

Function A to B - oil can flow. A to B - oil can flow.

B to A - oil can Dot flow,But, if pilot pressure is
But, if pilot prcssurc is thete, then oil can't flow
there, then oil can flow Iiom A to B.
from B to A. B to A' oil can not flow.
lql rFP (MSBTE) 2-41 Hydr. varv€s, Acruerors & access.

Pilot.teolreB checl Pilot-tcclosG checl

velve velve
Figure

Construction It consists of "spring It coDshts of "spring

toaded conical poppet" loaded conicsl poppet"
atrd "!ist n with a a.trd "ptut d with a
pusher rod" inside tlle pusher rod" i-trside the
valve body. valve body as show[ in
It ha-s three ports figure.
namely, Plessur€ port It has tbree ports
P, inlet port A alld namely, pressure port P,
outlet port B. iDlet port A and outlet
port B.
Working If oil under pressure ia If oil under pnessue is
supplied to port A, then supplied to port A, theD
the conical poppet will the conicsl poppet will
lift away ftom its seat, lift avray from its seat,
and makes passagE for arld makes p8$age for oil
oil to flow from port A to tr] flow from port A to
port B. port B.
If oil is supplied to If pilot plessure is given
outlet port B, then the to pilot port P, theo the
conicsl poppet will sit pisto[ will move toward8
fiImly on its seat, trot the coEical popp€t, to
alowiEg oil to Ilow to puah it to close the
port A ps.ssage, so that, oil can
Ifpilot pre$urc is given not llow from port A to
tD pilot port P, then the port B.
phton will move Ifoil is supptied t outlet
towalds the conical port B, then the conical
popp€t, to push it tD poppet will sit frrmly on
Eake the pa8sage for oil its seat, not allowing oil
to flou, from port B to to flow to port A.
Port A.
Application To lock the clinder to It is used in regenerative
avoid creeping of ove. circuit to i.Dcrease speed
mnning load. ofcylinder.
ET IFP (MSBTE) 242 Hydr. Valves, Acluators & access.

Pilot to open check valve :

a B

AloB BtoA lf pilot pr6ssur6 is

given, then oil can llow
lrom B to A.

Pilot to close check valve :

BloA AIOB
given, then oil can not

Note : Read secllon 3.26 lor hydrautic circuit showinq apptication

of pilot lo open check valve.
Read sectlon 3.18(c) tor hydrautic ckcuit showing
to close check valve.
@l',t" 2-43

2.1.6.5 3t2 Poppet Type Dlr€ctlon ControlValve:

. 3/2 DCV is uBed to oPerate single acting cylinder

(SAC)'
. The 68rrl€ shows 3i/2 spring return tlTe poPpet valve'
. It has a spring_loaded poPpet and a stem inside the valve
body.
When the push button i3
pressed, the st€m pu-shes the
poppet to open the Pa-ssa8€ for
oil to flow frorn Port-P to Port-
A. Otherwise, tlle Port-P i3
closed. T
In st€m position as shown in
Fig. 2.1.26(a), there i3 (a)
connection from Port_A to
port-T. Oil under Presaure
flows ftom single acting
cylinder to tank. Hence, the
SAC retracts. The inl€t Port
port'P is closed.
I
t-
When the push button is T
pressed, first, the stem closes
the port-T. This Position i3 (b)
shown in Fig. 2.1.26(b)
Further pessing t}le Push
button, as shown in
Fig.2.1.26(c), causes the stcm
to push the poppet against the
spring force. The Poppet vrill T
be lifted ofr frorn its seat
maldng a passage for the oil T

utrder pressul€ to flow from

port-P to port-A. Thus, the (r)
SAC exteods.
Fi$.2.1.26
 BTE 2-44 r. Valv6s, Acluatorc & access

"Poppet (seat) type valve', v/s .,Spool type vatve,, :

Sr. Poppet (Seat) *ype Spool t].!'e valve
No,
1 It is operat€d by oil under I t h op€rat€d by atry of the
pressuE and spri[g force. actuation methods
such as
manual, solenoid etc.
2 C,enerally, all .pressure Cretrerally, dl
"direction
contml valves" ar€ poppet coDtrol valves" are spool
tlTe
{or seat) type valves.
Only a few DCVs such as Check valve, U2. 312, 4t2, 4t3.
check valve, W and Al2 512, 5/3, 6t2,6r'3 et . all are of
valves are available ss spool tj?e.
tlre
3. It codsists of a sprirE
I t consists ofa spool inside the
loaded poppet sittins valve body. The spool positiotr
firmly on its seat closins may be shiftcd manuallv. bv
the flow passage. pilot prssure or by energizin;
Wben oil under pr€ssure the solenoid
is supplied from the other By shifiing the spool position.
end, the poppet will be the direction of llow of oil
lifted off from its seat and unde, prcssure gets changed.
makes a passage for oil to
flow
4_ iligh flou, due to larger Les s flow due to smaller port.
port.
5. Closed cr.oss.over : Open cFosa-ovef : During
While actuating the valve, actuation of the valve, there i;
first the exhaust port a tratrsitioD period in which
closed and then the ports get connected for a
pressur€ port opens. while.
I'bere is no transitioD
state.
6. Faster rcsponse. Slower respome,
7 I€Bs wear and More wear arrd tear
longer life. life.
8. Force requir€d f* Force requircd for acruatirg
actuatiDg the valve is the valve is less.
ffi ,rp (r serE) 2-45 Hydr. Valvos, Acluators & access

2.2 Actuators in Hydraulic System:

w-m12
what are actuaiors? How thoy aae classifiod? Draw and label
a double acting hydraulic cylinder.
w.2lt14
o What is actuator ?
Actuators are those componetrts of a hydrauiic system, which
produces mechanicsl work output.
They develop force and displacement, which is rcquired to
perform any specific tssk.
the tssk may be of any kind, such as to move, t-o press, t
lifi, to clamp and so on.
Sp€ed ofhydraulic actuators depends on rate of flow of oil.
Ratc of flow of oil under pressure can be contmlled using
flo\r coDtrol vslves.
Fon:e developed by a cylinder is the Foduct of pressure of oil
under pressure and the pistoE area.
We can contml the force of actuatoru by conkolling the
pressure of oil using pressure control valves.
By controlling the dir€ction of flow offluid, by using direction
coltml va]ves, can conhol direction of motion of actuatols.

2,2.1 ClassilicationolActuators:
92013
o. How hydraulic cylinders are classitied.
i2014
o. Give lhe d€lailod classificalion ol hydraulic acluators.
w-2014
o. Give the classilication of aclualors used in
Actuato$ are broadly classifred iDto two Eroups, Iinear
actuators and mtary actuator€. As the Dame tells, linear actuatorg
produce lin€ar motion and rotary actuators prcduce mtation.
Detsiled clalsifi€tioo is givetr in the classfication chart.
 @f ,'e (MS8TE) ?46 Hydr. Valves, Actuatorc & access

ACTUAToRS

A) Linear actustors B) notary actuators

l. LiDit d rotation
1. Rotating cylinder ectuators
2. Non-rohtirscyri'der l;i Xffjffi
(a) Single acting
cylinder i. Rsck and piniotr
G) Double acting cylinder t?e
ii. Chajn atrd sprocLet
3. Specisl type cyliDder€ t)'pe
6,:oDtitruous trotation
(a) Diaphragm cylinderu -'
i*.r.."
(b) Tandemrylinder (a) Ba8ed on directioD
(c) Double rod etrd cylhder i uniojirectional
(d) Telescopic cylinder ii. Bidirectional
(e) cytinder wfth cushioning tb) BaeT:T:3const.ucuo,,
i. Gear t],pe motor
ii. Vane t Te motor
iii. Pistotr type mot r
. ActuatoG ane common for both hydlaulic systems and
pneumatic systems. Only the difreretrce is, hldraulic
sctuatora are made suftcieDtly strong€r to withstand inside
oil prcssure a.nd to develop huge ,Dount offorce.
. Whereas, the pneumatic actuators are made lighter uling
aluoinum and Elatively thin cylirders as the inside
compreesed air pressure is ju8t about 5 bar.

2.2.2 Llnear Actuators (Cy ndoB) :

. Cylinders are linear actuatoE. T,hey pmduce linear motion,

i.e. reciprocation. Ttey contain a piston iDsid€ the cytinder.
When oil under pressur€ is supplied ftom one end of the
clinder, it exerts force on the pi_ston and heDce the pistDtr
Eoves to other eDd.
. There are two t,?es of cyliDders, narnely, rotating cylinder
and non-rotating cyliDders.
ffi,r" (u"u..) 247 Hydr Valv6s, Actuators & actess.

2.2.2.1 RotatlngCyllnders:
. Rotating cylinderu are used to operate work-holding devices
s"cl as chucLs. wherc the cvlinder being rotsting, t}re ptuton
is extended or rchacted using dircctioD coltrcl valv$'
r The entl coveE are fitt€d to cylinder on ball bearin$ with
omoer seal. The end cover€ at.e fi:ed and the cyliDder'pbton
assembly rotates along wil,h the splcdle ofthe machine'
. I\e piEtotr is contrectcd to the jaws ofthe chuck by meads of
levers. When the piston rctracts, the jaws move toward-s the
center to hotd the work-piece. When the piston extends, t-he
jaws Eo\.e away ftoD the center to release the work_piece'

Porl B Casing

llt !
I.4,
I ll,t

i seal
I I

Cylinder Bea ng
Fig.2.2.l
Rotati-oc cvli-nders are used ia chucks, couates. matrdtels ek
. ftofd- release the work-piece while the spindle is
-a
I'here is no need to stop tfie machhe lor replacing the work-
oiece. As sooD ts the job ir fi-Eished, just aiviag support to
itre ruor.lnsjot {by hand, wearing gloves) snd the lever of
airection colltrot valve is shift€d. ltrus the work-piece
released and rcmoved.
To mount the new work-Piece, just ias€rt it iD the chuck and
shift the tever ofDCV to other gide.
OoeratioD is very easy; there is no need to stoP the machine'
oo need of ctt ci k vs The tunctioD of loadiDg aod ualoading
the job is very quick; it saves the machining tifie'
m IFP lMSBTE) 2-4A Hvdr.

2.2.2-2 Non-Rotating Cy nders :

.I'hese are simple t]?e of cflindels. The cylinder is not

rotating; it is ststionary. The piston extcnds or Etr;cts
dependina
upon the di.ection of flow oI fluid. There are two
types of non-
mtatins cylinders, singte acting cylinder and d;;ble acting
cylinder.
A) Single ac ng cyllndsr I
w-2013
o. Draw a figure of actual construction ot single acting
air cy,ind€r
and lab€l it.
It is used to obtain line* .o""*u"i.
It has only one port, through whi€h the oil under
pressure is €dmitted into it, to move the pisron
in one
drection. PistoD will return or come back iue to spring
force.
3i/^2. is used to operaLe sitrgle acting cylinders
^DCV
{SAC)
Inlel Spnng

Head end Piston rod Rod end

Fie.2-22
Itllsstwo end covers, cap pnd cover and rod eod cover,
whrch covers rhe cylinder from borh ends and are
held
together by tie rods.
O-ring is provided between enal cover and cylincler
interface so as to ensure no leakage ofthe fluid.
cap,end is having inlet port for the oil under pressure
and the rod end is having a veDt hole.
A spriag is pmvided at tie rcd side of the cylinder for
retum stroke.'Ihe rod end is having a btrsb inside
wb,ch tbe piston rod slides. proper seals are pmvided
to prevent leakage of oil under pressure between
cylinder and pistoD.
m IFP (MSBTE) 249 Hyd r. Valves, Actuators & access

B) Double rq.$ng cyllnder:

. It is used to obtain lioear moveme[t.
. It has two ports, through which the oil under pressure
is admitt€d into in either direction, tD move the piston
in both d ections.
. That is, oil under pres6ure is supplied iom cap end
port for ext nsion of pistotr and it is supplied ftom rod
end Port for Etractioo of Piston.
. 4/2 direction control valves operate double acting
cylindeB.
. In first position ofepool of4/2 DCV, oil flows to cap etrd
port of the cylinde! and coltres out ftom t}e rod end
port. Hence, the €Ytinder extends'
. In eecond Position of spool of 4/2 DCV, oil flows to rod
etrd port of the rylinder and comes out from the cap
end port. Heme, the cylinder retmcb.

LLLJ-

\NS

I.ie.2-E
Constiuction :

. Ithas two eDd covers, cap end cover and rod end cover,
$rhich covers the cylinder &om both ends and are held
together by tie rod.s.
. O-ring is provided betwe€n erld cover aod cylinder
interface so 6s to eDsure no leakage of the fluid'
r Both end cover€ have ports tD admit the oil under
pr€$ure in to the cylinder itr eitier direction'
o The rod end cover has a bush inside which the piston
rod slides. Proper seals are provided to prevent
leakage of oil between cvlinder and pkton
 Eff,', 2,s0 Valves, Actualors & access

Packing friction :
. In case of cylinde*, the piston is tightly inserted in the
cylitrder. Due to rubber piston seals and tight fitting, it
requires some amount offorce juBt to move the piston.
. The Einimun) aEount of force which is rcquir€d to
move the piston itr cyliDder under no load conalition is
called packing fi-iction.
. cenerally, packing friction is considered to be same for
both ext€nsion and retraction. I.hat is, same amount of
force is required to pull as well as to push the piston in
the cylinder under noJoad.
. Net force required = working load + packiDg friction
Ex.2.2.1 The prossure at no load condition durino extension
of
DAC is
150 N/cm' and that during relraction is
250 N/cln,. DEmeter of pislon rod is 2.5 cm. catcutate
bore diameter of cylinder and packing Idction.
Soln. :
Data : Pilton rod diameter = d = 2.5 cE
No load conditions
Pr€ssure during extn. = pe = 1SO N/cm,
Pressur:e during retn.
=
pr = 2b0 N/cm,
PistoDdiametc.=D=?
Packing friction = FR = ?
Force during €xtn. Force duriqg r€tn. packiog liiction
= =
(PexA) = tprx(A_a)l
...( Pe x D, )= tPr x (D'_ d,)l
...(1E0xD,)= 1250 xlI], _2.52y1
... Borc diameter = D = B.9E cm

Packing frictio = Pe,A=pe '

'4
= ,_-
fl xA.95,
rcu x ---Z- = l83Z N
ffi IFP {MSBTE) 2-51 Hydr. Valvss,

Ex.2.2,2: ll diamsler ol piston is 60 mm, diam€t,er oJ pi$on.rod is

10 mm, and air prgssure is 100 N/mm'' wnat wll De m€
torc€ in advancs strok€ and retum stoke?
Soln. :
I)ata: Pistotr md diaDeter = d = 10mD
Pieton dis.deter = D = 60 mm
Pressut€ duting extn. = Pe = l0o N/mm'
Pressure duiing retn. = Pr = 100 N/mD'z
Force duthg extL = Fe = ?
Force during ertn. = Fr = ?
,tDz 3.14 x 6e
Area ofpiston = A= 7=!T=2826t - D'
ttD'2 e?
ai 314x 10'z zs s mm'
Area of pbton rod = a = = =

Force during extcnBioD = p x A = 100 x 2826 = 28260 N

Forte duri.Dg retrac'tion = Px(A-a)
= 100 x(2826-78.5) = 274750 N
ex.2.2-3 i A double acling cylinder ol boro
diametor I cm and piston rod diameter
3 cm is used to litt 5 ton load dudng
extension. The cylinder i5 mounted
verlically as shown in figure. The
weight of plattom assembly rs 850 kg' B
Packing ldction behvson pislon and
cylinder is 150 kg.
Calculate pressur€ reliel valve setting
end counler balance valve seltlng.

Soln. :
(a) Ourlng llftlng tho losd :

Durfug liftiag itr upward <lirectioa' load, ptatform weight and

packinJ fiction all ate in opposit' direction to the motion'
Force required = load + platf,ortn weiSht + PacLiDS frictiotr
= 5mO + 850 + 150 = 6000 ka
 2-52

pressure oroir requir€, ri

= i = ## = :gg, = .,s.42 ba/cm2
Generally pressure relief valve is set lor 1.25
times the
marrimum working pressure.
So, reliefvalve setting
= 1.25x11g.42 = 149.27 kCcra2
(b) During towering the toad :
While lowering the load in downward direction, toad,
platform weight are in the direction
of motion and only
packing fi:iction is opposing the motion.

Force rcquired = - load - platform weight + packing friction

= - 5000 _ 850 + 1S0 _ 5700 kg
=

Pressure of oil required F 4xF 4x(.s700)

A-a [^(Dz_drr- ?rx(8,-3r)
- 132.02 kg/cmz
Note. herc that, during rctmction, negative load (over-
running load or run-away load) is causing
the .egative
pressure,
CouJlter balance valve is essential to overcome
talling of
load, and it should be set for 1.3 times
the load induced
pressure (LIP).

Over running load= load + platform weight _ packing

fi,iction
FI
= 5000 + 850 _150 = SZO0 kg
Load induced pressure (LIp)

_ Over-running load Fr
Area ofpistoD =A
_ 4xFI
= nrDP _4x5Z0O
=-;;-= 113.45 kglcm'

So, counter balance valve setting 1.Ax11g.45

= = I47.5 k7lc,r]
El ,t" (r""tu) 2-53 Hydr valves. Actuators & access.

Ex.2.2.4 | Force reourred dunnq exlension ol DAC ot a hydraulic

oress to ounch h6 rolk'piece rs 5200 kg. The DAC is
hounled vertically as shown in figure Oiameter ol
oislon is 6 cm and drameter of piston rod is 4 cm.
;nsrder packing tnction as 180 kg and weighl ol punch
assembly as 500 kg.
Calculate lhe pressure ol oil required _::-
for punching. Determine lhe pressure
reliet valv6 setling.
Calculate the pressure ol oil before
punching during 6xtension, whother
B
I I
aounter balance valve is nec€ssary? lf
so, v,ihat will be its pressure setting?
Calculate the pressure of oil required
lor retraction.
Soln. :

(a) Durlng aclual punching in downward slroke :

Durina actual punchinS, punch s.ssembly weight is over-
rulning load, punching force and packing friction are
opposing load.s.
Force required = punching force + packing friction - assembly
weight
_ 52OO + 500 - 180 = 5520 kg
F 4xl' 'lx552q- rrg.42kgr.62
Pressure ofoil= E=rr.il= rr8,
so, pressue r€liefvalve settiry = 1.25x119 '12 = 149 27 kalco'z
(b) Durlng extsnglon ln downwud dlrsction :
During advatrcement of punch towards work-Piece, punch
a-ssembly weiaht is over_running load, Packing friction ia
opposing load.
Force required = ' punch assembly weight + packing frictiotr
_ _566* 166=-320ke
t;!3?o'
pressurcorol=
I= #+ = = -11-32k4cm2

The Eegative load (over-runaiag load or run-away load) is

caueing tlre negahve pressure.
 rFP ( 2-54 Valves, Actuators 8 access.

Counter balance valve is essential to avoial over-running of

the cylioder, aid it should be set for 1.3 times the ;ad
induced pressure.
Over ru ring load = punch assembly weight packing frictiotr
-
= S00 + 180 = 920 kA
Load induced pressurc (LIp)
Over-runnins load
piston - area olpiston rod
_ Fr 4,Fr _4ag2o
= A-a =; 1p=, =f,, 1Pl4rt= 20.38 ks/cm'z
^
So, counter bela.oce valve setting k/c[ 2
= 1.3x20.g8 = 26.49
(c) Ourlng retracdng ln upward dirrcfion :
While rehacting itr upward directiotr, both punch assembly
weight and packing &iction are opposiag loads
Force required = punch assembly weight + packing friction
= b00 + 180 = 680 kg
*___.... "., F 4yF 4)(680)
- A-a - r y (D,- d,) = rlplli1 = a3 3ttEc6'
Ex. 2.2-5 Cuflingjorce req uired during extension olDrc ola
hydraulic shaper is 750 kg. The cytinder is mounted
horizonlally as shown in figure. Piston diameter is 4 cm
and pislon rod diameter is 2 5 cm. Packi ng friction is
100 kg. Rato of flov{ ot oit is l 50 cmls. calculat€ the
Iollowing
1 Pressure of oil during cuttinq stroke
2 Speed ol toolduing culting stroke
3 Pressuro ol oil during return skoke
4 Speed ol lool during relum slroke

t-

FiE P.2.25
ffi IFP (MSBTE) 2-55 Hydr. Vatu6s,

(a) During cqtting stroke :

. Force required during cuttilg = cutting force + packing

friction
= ?50 + 100 = 850 kg
. Pressure ofoil duning cutting
4 'F:-4^85:o
'- E-
A'nxD2' xx42 =67.6i
kercmz

. Speed oftool during cuttiDg stroke

4'q =414=
-- qA =-rxD'- rr.ga
,rx4' "r,,,,"

(b) During return etroks :

Force required dunng retum

= Packirg friction = 100 kg

Pressure of oil during retum

F 4xF
nx (D'- d')
4x100
13.06 kglcm'
= U' - 2.6') =
^,
Speed oftool du.ing return
_a = tx(
1 x0
-d':)
4x100
' n\112 - 2.52\ = 19.59 crn/s

. ln hydraulic shaper, we need slow cuttitrg shoke and

fast rcturn stloke.
. ln this example, sPeed during cutting stroke is 1194
cm./s, altd speed during rcturn stroke is 19 59 cm/s'
. Retum shoke is 1.64 times fa6ter than the cutting
shoke by default, witiout using meter_in oi met€r'out
cituit.
. Fo! reducing tle cutting BtroLe if needed, s
speed of
flow control valve may be used, and meter_in or meter
out circuit can be made.
ffi,t"r, 2-56

2.2,2.3 Other Types ol Cytinders :

w-20t3
o. Sketch and lab€l lino diagram of pneumatic diaphragm

(A) Olaphragm cylnder:

. t:"9 are used for very smal disptaccEreols. There
w'rl be a diaphragE iDstead of piston iNide tbe
cylinder.
. The diaphragD deflects when oil under pressure
is
admitt€d into the cytinder. me aapt*gin is nitJ
with a piston rod and he""e the piston mi
o.
retracts. "*tenrls

FiE- 2.2,4
(B) Doubte rod end cytinder :
o These cylinders have piston rod on both sides
of the
pist n as 6howD in the Fig. 2.2.5.
. By
Jhls snaDgement, work is carried out on one siale
and the other side is u.sed to operate limit swit h
and
limit valves.

Fig.2.2.5
W) re1 MSATE) 2-57 Hydr. Valves, Actuators & accsss.

(C) Tandem cyllnder :

w-2013
o. What is tandem cylinder ? Explain wilh neat sketch. Draw
of it
Here, the cytinder is divided into two or more
compartEents. f'here will be piston in each
compartment.
All pistom are fitted t! a single piston rcd as shown in
Fig. 2.2.6. Tandem cytinders are used to produce more
amouBt offorce.

u I I
wP. I I'
Ftg.2.L6
(D) Cyllrd€rs wlth cuahlonlng :
. If the cylinder is lon8, that i-s, if shoke lengtl tu more
aod the speed is high, tien natu$lly, the piston-
impact on end-covers is considerably high.
. Continuou.s hamneriDg of piston oD these cover-plstes
causes looEening of tie rcds aDd lealage of fluid. A.lso it
will damagB the cover plat€s. Heace to avoid Eudden
impact of piston on the cover plates' cylinders with
cushioniag are ured.
. A cylinder with cushioDing is shown in Fr9.2.2.7.lt
has intcgral flow contlol valve a[d checL valve in its
end cover plates. The piston rod has a projected Dose
equal to the drameter of inlet port pa$a8p.
(a) Dnring retraction :
lvhen the piston is moving towards left, once the
pistoo Dose enteE the port, the pa.ssage closes. Only the
rcstricted passa8p through tle FCV is left, and hence
the flow r€duces rcsultin8 in further moveEeDt of pfuton
slower. This is hov, the cushioDing (slow end of strcke)
is achieved.
W IFP (MSBTE 258 H r. Valves, Actuators & access,

Fle.2.Z.7
(b) During extension :

. During ext€nsioo, when the pistoD is EoviDg

towad-s right, oil under prcssure is supplied to
"port- A".
. Now, since this port is closed by the nose, oil has to
flow tbrough the rcstricted passeg€ of FCV. It will
not produce suffcient force to stsrt moveEent of
the piston.
. HeDce check valve is provided through which, oil
under pressure flows freely, and move the pistoa.
(E) Telslcopic cytindsr :

s.2o1 1, 2O1 2, W_2O1 1, 201 3

o. Draw and explajn the working ol teloscopic cylinder.
w_2014
o. in lelescopic inder with sketch
Telescopic cylindeN are used in cranes and hoists to
lifi the heary objects to gre3ter height.
A telescopic cylinder codsists of two or more number of
cylinders, one inside the other, which extends one by
one sequentially when oil is supplied under pressure.

HeDce, a compact talescopic cylfutder will extend to

g€at€r length. Fig. 2.2.8 shows 6 telescopic cylinder.
ffi,t" 2'59 Hydr. Valves

fl9.2.28
(O Cyllndor8 wlth a.ntal :

. For autorrahc continuoua 6.trd sequential operatron of

cylinders, it is needed to eenee the displacement and
positioa of pistotr of one cylinder and the siStla.t output
is given as ilPut to the other.
. SeDsors are us€d for this purpce. lhere are several
Wpes of s€Dsbg devices; some of them arc givetr below.

Limit rtelves : Ihey open when the cam oP€rstes the roller
and supplies oil uader pressurt to the pilot
operated valv6.

Limit svritche3 r Makes etectric supply "oD" when carn

operat€s the mller snd supply cuEent to
solenoid operated valves.

Opticel Bensora : lteBe are photo-electric sensors which

seue the light rays and produce electric
sipal, which is amplified and grven as
ioput siglal for soleaoid valv6.

Electronic I'hese sensors s€nse the ma€Detic field of a

perEaDent magnet 6tt€d tD the piston, and
produce electric signal, which ie amplfied
and giveB aE input siSna] for solenoid
W IFP (MSBTE) 2-60 Hydr Valv6s, Acluators E access.

2.2.2.4 CylinderMountngs:
s-2013
O. Enlist ,ou. ol
Several t,,pes of cylinder mountings are used to mount the
cylinder in oil under pr€ssure power systems.
The performance and life of cylinder depends on the way in
which we mount the cylinder.
National Fluid Power A.ssocietion (lJtrpA) has given
nearly 24 t)'pes of cylinder mountings. Some of them are
studied below.
Cyliade? mountingB are classified as follows :

a) Cap end side

1. Tie rod extcnded : b) Head end side
c) Both end sides

2. Squar€ flange type a) Cap end side

b) Head end side

3. Rectangular flange t1'pe a) Cap eld side

b) Head end side

a) Foot side
4. Lugs typ€ b) End side
c) Cedtrc-lhe type

a) Cap end side

5. Turnnion type b) Head end side
c) Int€rmediate

6. End atrgles type

7. Cap etrd clevis
8. Cap end eye
Ef ,." (us"r.) 2-61 Hydr. valv€s, Actuato6 & access.

IigurGs of dilTcrent types ofcylinder mounlings

n.rg.
/;

,1. LUC!
ffi ,r" t,r""t., 2-62 Hydr. Valves, Actuators & acc€ss.

2.2.3 Rotary Actualors :

9201'
O. Stals ttlo dlfarenl types ot air motors. Explah any ong.
w-m1t
o. with neat sketch ot air molor.

2.2.3.1 Limlted Rotatlon Aciualors ;

These moto$ are bi-directional Eotors. Itrey can run in both

directions, but for a linit€d trumber of rotatiotrs.
A) Vane type :
. Fig. 2.2.9 shows vane type limited rotation motor.
. It has a cylindrical block rittr a pairs of finely ground
flat vanes in its rsdisl slot.

Fia.2-2.9

tlrouah port-A, it
When oil utder pressure i3 supplied
exerts pressure on the vaaes and hetrce, the Dotor
shaft rotate in counter clock-wise di€ctioE.
When oil under pressur€ is supplied tbrouSh port-B,
the motor shaft rotates in clock-*'ise direction.
W'r, 2{3 Hydr. Valves, Aclualorc & access.

B) Pllton typ€ (Rsck and plnlon typ.) :

. Fig. 2.2.10 shox,s vane tvpe limit€d rotation motor.

. lt has a ryliader iDside wbich, two pistons aIs
mounted.
. CoDnection &om port-A is talea ftom either etrd of the
cylinder as showtr in figure.
. Connection to port-B is taken at the Eiddle of the
rytinder.

t
fi& 2.2'10

Wher oil under pressurc is supplied tbrough portA' it

exerts pressute on the pist Ds from either ends ofthe
cylinder.
I'he pistons move towards each other. Oil floFs out
throuSh port-B at ttre middle ofthe cylinder.
The pistDDs ar€ fitt€d wit}l ract 8nd pidon
arrangement. Hence ttre pinion rotat€s in counter
clockwise dircctioa.
when oil under prcssure is supPlied throwh port-B, it
ererts pr€ssure on the pistotrs from iDEide out of the
cylinder.
The pistotrs Dove away from each other. Oil flows out
t}mugh port-A, heoce the Pidon lotstzs itr clockwise
diiectioa.
El,r" rr""-.) 244 Hydr, Valves, Actualo6 & access

2.2.3,2 Continuous Botatlon Actuators (Rotary Motors) :

. These motors can run continuously.
. A[ rotary pumps are motors, ifoil urder pressure is supplied
to the port ofa rctary pump, then its shaft rotat€s.
. Botary motors are bidircctional. If ir et and outlet
connections are iDtercha[ged, they caJl run in opposite
direction.
A) External Gear Motot:

*mr2
o. motor with neat sketch.

Fig. 2.2.11 shows an ext€mal gear motor.

It consists of two spur or helical gears, which arc
meshed with each other, aad ar€ mouated inside the
casing.

t
tLt
FiE-22-lt
When oil uuder preasure is aupplied to the inlet, it
exerts force on the gear teeth, due to which g€als
rotet€, shali mtat€s and oil uader preesure comes out
flom the outlet
@l (rsut.) 245 Hydr, Valves, Aclualors E access.
'rr
B) lntemal Ci€rr llotor :

. It has tv{o gears i.e. ooe is having external teeth and

the other is having iot€rtral t€eth.
. I'he extemal gear is inside the int€rtral gear. The two
gpars are itr mesh with each other. A cresceDt seal is
provided between these t*,o gears, which fills the gap
beh{eeD the two gEar€.
out t
f
4
+ s

FiE 2.2.12
When oil under pressurc is supplied to the inlet, it
exerts force on the gear t€eth, due t which g€ar3
rotqt€, shaft rDtates and oil under pressur€ comes out
from the outlet
C) Lobo Molor:
I'his motor is similar to ext€mal gear motor. It consists
of treo lotors, cslled lotres, {,hich are in mesh with each
other and moudt€d inside fhe casing. These lobes have
very Iess truEb€r of'teeth' (may be two, three or four).
When oil under pressure is supplied to the iDlet, it
exert€ force on the lob€ teeth, due to which gears
rotst€, shaft rotates and oil under pressute coEes out
liom the outlet.
@f ,r" luset y 2-66 Hydr. Valvss, Acfuators & accoss

hlsl
FiE 2.2-13
D) Generated rotor (Go-rotor) molor :

This motor clnsists of two getrerat€d mtors a6 shown

in the Fig. 2.2.14.
One is having extemal teeth and other is havirxg
ht€rnal t€eti.
the rotor with external teeth mtates inside the rotor
having iDtemal t€eth. The inner mtor is havhg oae
t oth less than that ofout€r mtor.
Casing

€
O!llel
€

FiE-22-14
When oil under plessure is supplied to the inlet, it
exerts force on the geai t€eth, due to which gears
rotat€, shaft rctates and oil under pressure comes out
from the outlet
ffi ,., ("s"r.) 2-67 Hyd r Valves, Aclualo6 & acc€ss

E) Unbalanced TYPe Vane Molol

w-mt2
O. With a nsal sketch, explain construction and wofiing of vane
air motot

It ofa cylindrical mtor, which is mounted with

coEsist€
sn offs€t ilside a circular casitr8.
The vgnes ar€ seated in the radial slote ofthe rotor and
held agaitrEt the c€.sing by spring or hydraulic force.
Hence there will not be any leakage of oil between tie
vaDe tips a[d the casiDg.

rnrer + + o,xter

fis.2.2.15

Wheo oil under pl€ssure is supplied to the ir et, it

exerts force on the vanes, due to which cylindrical
rctor rotat€s, shaft totst€s and oil under presaure
comes out ftom the outlet
g1l rFp (MsBrE) 2-64 Hydr. Valves, Actuators & access.

D Balanced Type Vano Motor:

. In this t)'pe of motor two iDlets atrd trvo outlets ai€
eEployed.
. The center axis of the rotor and that of the elliptical
casing are the same.
. Pressur€ loading still occtrs, but the two ideDtical
halves ofthe motor creatcd equal but opposit€ loads on
the motor shafts and bearitrg.
. Hence, balaaced vane motor gives b€tt€r service add
laryer life compared to unbalanced tJTe vade motor.
odbl
f

I
Out t

FiA.2.2.16

When oil under prcssure is supplied tD the inlet, it

exerts force on the vanes, due to which cytindrical
rotor mtates, shaft rotatcs and oil under prcssul€
comes out fiom the outlet.
 Valves. Aclualors & access.
@1,', 2-69

G) Slralght Axl! Plston Motor :

. Straight axis pistor motor is shown in Fig 2 2 17'
. In straight sxis piston motor, the cylinder block i3
fitted to the diive shaft, i.e. the axis of mtstion of
mtation cyunder block aDd the dtive shafr ar€ saoe'
. The shoe pLate i5 mounted on a swash platc, which is
fixed at an angle to ttre sxis of mtation'
. The angle of swash plat€ cao be varied to change the
speed ofthe Botor.
r When oil undei pr€ssure is supplied to the inlet, it
exerts force on the pistons, due to which cyli.oder block
rotstes, shaft rotates aod oil under pressur€ coEes out
from the outlet.

Cylindsr
Shoe plale

e u- II
Out

+ w! I r-a
ln
mI
tsig- 2.2.17

tl) Benl Axis Pislon Motor:

. Bent axis pistoD motor is shown in Fig. 2.2.18.
. Ia bent axis piston motor, the sho€ plate is fixed to a
flangp; the llangp is keyed to a diive shsft The axis oI
cylinder block alld that ofthe flange are iatersecting at
an angle. A unive8al Iink couples the flange and the
cylinder block.
l(Pl rrp ru SBTE) 2-7O Hydr. Valvos, Actualors & access.

Iig.2.2.lt
. When oil under pressure is supplied to the inlet, it
exerts fo.ce on the pistons, due to which cylinder block
mtstes, sha.fi rctat€s atrd oil uDder pr€ssure comes out
fiom the outlet.
D Ststlonary cyllnd€r .adill piaton motor :

w-arl1
O. Draw a n€at sketci and exptajn wo*ing radial pislon type
molot,
Frg. 2.2.19 shows 6 ststionarlr cylinder tjlpe radial
pistol motor.
It coDsists of a statioDary cytinder block, in which, five
cylinders sre airanged coplanar vrith equal angle
b€tween them.
Toblly ther€ ar€ five pistons, one reciprocatitrg inside
each cylioder.
All pistos ane coonect€d to a single craok by
individual connecting rod-s as shown ir Fig. 2.2.19.
AIl suction valves aI€ coroectcd tr s single suction pipe
and all delivery valves are coDnected to a single
delivery pipe.
ffi IFP (MSBTE) 2-71 Hydr. Valves,

FE 2Zt9
. When oil rmder pressure ie aupplied t' the iDlet' it
exerts foIte on the pistoas, due to *hich cylinde! block
rotstes, shaft iotstes aDd oil under pressu? coBes out
ftom the outlet.
J) Rotltlng cylindlr tyPo Rldbl pldon rptor :
. This 6otor consists of rotating cylinder block' which is
mouDted with atr o[&€t hside a c€sing'
. The casing has a reaction ring with which, the pfutois
remains i; contact while t'he cytiod€i bloch is rotatitr8'
This ie achieved by cenkifirgal force and pressure of
liquid-

FiC.2.2.m
 Valv€s, Actuators & access

The pistons ane assembld inside the radial borcs of

the cylinder block, iDlet port and outlet port ar€
Iocated as shown in the Fig. 2.2.20. T$o ports are
separatDd by pintle,
When oil under pressur€ i_s supplied to the inlet, it
exerb force oa the pistoDs, due to which cylinder block
rotates, shaft mtates and oil under pressure comes out
from the outlet.
2.2.3.3 Comparlson between Hydraulic pump and
Hydraulic Motor :
s". i Hydraulic pump Eydraulic lrotror
xo. l

1 Pump pumps tlre oil to the Motor pmduces rotatio[

hydreulic systch. and torque.
2 Hydraulic pump converts Hytlraulic motor
mechanical energlr' into converls hldraulic
hydraulic energy. oner$r into Eechanicsl
etrersr.
3 Eydraulic pump is work Hydraulic motor is rvork
consuming device. prcducioa device.
.t When the sheft of hydraulic Wher we supply oil
pump is rotatcd by means of under Fessure t the
any prime mover, it sucks oi1 hydraulic motor, its
fr'om the r€servoir and delivers shali rotat€s.
it to the hy&aulic syst€h. It produces rotation and
torque at iLs shaii.
5. Construction of pump a_ud Construction of rnotor
motor are similar. A hy<lraulic and pump are similar. A
pump can work as hydraulic hydmulic motor can
work as hydraulic
pump.
6 Application : to pump oil to Application : to have
the hydraulic system. rotar'Jr motion in aay
hydmulic system.
@f MSBTE) 2-73 H valves, Actualors & access
't"
2.3 Pipe Materials for HYdraulic Systems
9m13
O. Enlist various matsrials us€d tor hydraulic pipos.
O. How hydraullc pip€s are classili€d?
O. wllat ars tho various types ol hoses Used in pneumatic
sysl€m?
w-z)r3
O. What are tho of used in ?

A) Rigid pip$: Cast iron,

Lw carboo stceb,
Alloy steel6,
StsiDless Bt€el,
Copper and its alloys,
Aluminum and its alloYs.
B) Flerible hoses Ylon braided hoses,
Stcel wire reiaforced rubber hoses,
Poly-uretiene tubes, NYIoD tubes,
polyethyteDe tub€s, PVC tub€s,
polypropylene et .
C) Accordhg to strength Stsndad pipe (STD)
Extra strotrg pipe (XS)
Doubte Ertra stroDg PiPe (rQ(S)

2.3.1 Flexlble Hose:

w-2t 11

O. Whidr lnalsrials ate usod lor layers ot hoses in pngunlatic

sygtgm. Draw cross seclion ol pneumatic hoso pip6'
w-2t13
O. Drary construc'tional delails ot pn€umalic hos€. Why hose is
ired in neumatic circuits.
 2-74 Hydr. Vatues, Actualors & acress

Flexible hose pip€s are ext€nrively employed itr hydrauiic

systems and paeumatic system! as they sr.e easy to
accommodate and to cotnect with in the svailable space.
these pipes arc made of elastic material atral can be bent
easily.
Fhnble pip€ is dade of sev€ral layeE with metsl wire
braiding between ttrem. Thos metal wirc EinforceEedt
incresses the strength ofthe pipe.

E6 9e BO
9;
PE -q:
9a
E}
;i
JE
g
Fis. 23.t

Layer Function Materid

Tube Convels the hy&aulic Polyethylene
oil
First Prctects and Metal wire (steel or
reinforc€met!t strengtheDs the tube copper)
Adhcsive Holds the Rubber
layer reitrforcement layel€,
pmtects agaiEt
vihations.
Second Pmtects the first Woven yam (cotton,
reinfor:cement rehforcement Dylon, polyester
syntletic fiber etc.)
Pmtects boD Polyethylene
abrasions, duBt,
vibrations, su.nrays
@ tFP MSBTE 2-75 Hydr. Valvss, Actuators & access.

Advanlagor ol noxlbl€ plp€a :

. Fl€xible pip€3 can easily bent and accommodatcd in the

available space
. It mskes the systeD simple sIrd compact,
. It c€tr be fitt€d to moving coBponetrt3, a riaid pipe can't.
. It has hiSh streagtl aDd less weiSht.

. It has Sood iesistaDce to corrosioa, 6re, moistuie, abraaiotr

and penetration.

. It ab6orh6 vibratioD aDd noiao.

. It compensatei for thermal erpaneion and contraction.

. Aligtrment is essy and accurat€.
. Suitsble foi wide ratr8e oftemperature-
Diradvantsgca ol lloxlble plp.! :

. Coet is high.
. Need proper support.
. Other coxoponents csnnot be mou[t€d taking its support.
. Use of mole number of fleribte pipes makes the systrm
cluDsy and s.ffects the aesthetic view of the system.
2.3.2 Requlr€monts ol Fluid Pow6r Plumblng :
s2012
O. What are tho requiremenls ot good oal undor pressure power
plumbing?
s-20r3
O. Hoyr good piping system is designed. State their tips.
w-2013
O, write four tips ror ln neumatac
ffi ,r" (r""r.) 2-76 Hydr. Valves, AclualoE & access.

Following poinb are t be considered while desigring a

hy&aulic piping systeE.
1. The conductor (pipe) must be ofsufficieDt sheogth to cotrtain
oil under pressur€ at desircd workidg pressurc, to resist the
highest posBible shock pressure, and to support the devices
that arc mou-ntsd on it.
2. The tcrmidal point€ (unioru, flarges etc.) must be provided
at all junctiotrs to achieve easy removal or dismantury or
maint€nance.
3. Port seab should be designed to reduce oil under pr€*suc
losses.
4. The coDductors must have smooth intemal surfaces to
reduce loss of power due to friction.
5. Correct size should be used which causes best flow
conditions.
6. Use of elbo*s, bedds, reversals etc should be as less as
posBible.
7. Use of manifolds reduces the Deed of joints and lengthy
pipes, thus it improves the s,.stem's efficiency.
8. The lineB must be kept clean and fluehed regularly.

2.3.3 Requiremenl ol Hos€3 and Hoss Finlngs :

1. Hoses should be flexible sumciently.
2. Hoses shorrld be able to work with maximuB system
pressute.
Hoaes should be provided with proper eDd fitting.
4. Hoses should be oil r€sistaht.
5. The inner tube should be oil resistart seamless tube of
rubber.
6. The irEer tub€ should b€ braided with wires of rsyon, t€xtile
or steel for reinforcement.
7. Itre outer cover should b€ oil and weather resistant.
8. While a$embling, care Bhould be taketr to avoid sharp
bend.s, twist atrd t€nsioD iD the hose.
9. Care should be talen while rnstallation rcgarding the
permissible limits of tempemture, which the hose can
withstand.
El',0" tu."r.r 2-77 Hydr. Valves, Actuators & a@ess.

2.3.4 Plpe Slze Specilication :

s-2012
o. ('l) Standard pipe (2) Exl.a strong pipe
C,eDerally, pipe size is sp€cified in the follo$ing three ways :

1- NoEiDal pipe size (NPs) : This nuober indicatee the base

diametcr of pipe in inches.
ExaDple : % inch, % iDch, t hch, 11, ioch et .
2. Schedulc (SCE) : This numbel is ba3ed on wall thickress.
Gr€at€r the SCH, greatar will be the wall thickness of pipe.
A schedule numb€r indicstes the appmximata value of
100xP
s
Where P = s€ryice plrssurc and S = allowable strcss
Er.mplc : SCH number 5, 10, 20, 30,40, 50, 80, eta...
gchedule 4, t0
and 160 art widely used.
3. Pipes aie also cla$i6ed ss StaDdard (Sm), extra strodg (XS)
size, double extra strong OO(S) based on strength.
. Sm is neaily equivalent to SCH 40,
. XS i-s trearly equivaleat to SCH 80,
. )O(S is nerrly equivalent t SCH 160.
For any NPS aumber, OD (out-er diamet r) is fixed.
WitI iocrease ia SCH number, ID r€duces and thiclnesg
iac!€ases.
&ample :
. For NPS of 1 iDch, outcr diametar is 6xed, equal to
1.315 inch.
. But, inside diadeter i6 1.049 for SCH40, 0.957 for
SCH80 and 0.815 for SCH160.
. Hetrce pipe wall thickness is 0.199 for SCH40, 0.179 for
SCH80 strd 0.25 for SCH160.
ffi,r, (r""t.) 2-74 Hydr- Vafuos, AcluatoB & accass.

Table showing pipe size apeciEcationa :

NPS Type SCH OD ID inch Ihicknesa

inch illch
STD 40 1.315 1.049 0.133

1 inch xs 80 1.315 0.957 0.179

)o(s 160 1.315 0.815 0.25

2 inch STD 40 2.375 2.067 0.154

xs 80 2.\',t5 1.939 0.218

)o(s 160 2.3'.t5 1.689 0.343

STD 40 3.066 0.216

3 inch XS 80 2.9 0.3

)o{s 160 2.626 o.437

2.3,5 Varloua Losaes in Pip€a:

1 Major loss of head due to friction i! pipes, carl be calculated
by uBing differcnt formulae, or using Nomogram.

2 Minor losses are due to pipe fittitrgs (such as bends, elbow,

valves etc), the valves and fittingE are given by the
manufacturer, and are "exFessed in the equivalent lengttrs
of straight pipe oftlle same diaEeter".

Heid loss due to leshage.

4. Hesd lo€3 due to bmletr eeals.

5. Head loss due to wastag€ ofair

ffi ,t" tu""t.t 2-79 Hydr. Valves, Acluators & access.

2.3.6 Pipe Fittlngs and Tube Fittlngs:

w-ml2
O. Namo any eight pip€ ard lub€ fitti.gs. Write their turElion in
bdet.

Pipe fittings ar€ the coaDectors r€quired for coDnectiDg the

pipes atrd tubes. Trere aie variouE kinds of pip€ fittitr8B deperding
on the applications. There is very small amount ofpcssure loss in
any pipe 6tting, but when mady numbers of fittings arr tier€ iD
aDy cirEuit, the cuoulative efiect of these lo6s€s is coBidersbly
larse.
Sr. \pe of Application
No. Fitting
1. Male connector This fittilg is us€d t,o connect pip€y'tube
to threaded hole ofthe manifold.

2. Female This fitting is used to connect pip€^ub€

to nipple with ext€rnal thread.

3 Tee Ibis nftiag is used to coDDect tbr€e

prp€s.

4. Cross This fitting i6 used to connect four pipes.

5. Elbow This fitting is used to have sharp riSht
aagle turD itr the pipeline.

6. 45 desre€ elbow tlris fittin8 is us€d to have 6hsrp 45

degree turn in the pipeline.

7. Bend This fitting is used to have long radius

curved right atrgle tur:n in the pipeline.

a. Reducer This fitting is used to coDnect two pipes

of differcnt diam€tels.

9. Double nipple ltris fittiDg is used to cooDect two pipes

havinc intemal threads.
10. Plug This fitting is used to close the ports.
Eff,r, (r"ur.) 2-AO Valves, Aclualors & acc6ss.

2.4 Seals in Hydraulic System :

I'he main function of sesl is to avoid leakage of pressurized

fluid. laakage may b€ oI two types, intemal leakage and
external lealage.
External leakage can be easily traced out, it is seen hom
outside. External leakage results in wastage of prcssurized
fluid. In hydraulic systems, extcrtral lealage causes slipp€ry
floor, dirty surroundings, accidents and 6re hazards.
Intcrnal leakage is difficult to detect, it happens inside the
system, it can't be seen from outside. Internal leakage
,esults in rcduces efficiency, power loss and reduced load
carrying capacity.
2.4.1 Classlrlcatlon ot S6als :

s?013
O. Sketn ths clp seal, and wrile ils applicatioos.
s-2ar'r4
O. Dilierentiate between static seal and dynam:c seal

A) Accordlng lo the method of soallng

. Positive seel I perfect Bealing, 100% leak-proof. Not
evetr a mhut€ drop of oil can pass tbmugh it.
. Non.poaitive Beal : allows a sma]l a$ount of leakage.
This tealaCe of oil serves the purpose of lubricatirg
the spool in-side t}re valve.
8) Accordlng to the appllcallon :
. Static sesl : used b€tweetr mstiag parLs having no
rcIative movement.
. Example : Seali-ng betweeD Flang€s, ga.sket etc.
. Dynamic s€ol : used between mating parts witl
relative motion.
. Exampte : Lneal ootioa seal between rod end cover
and piston rcd, rotary motion seal between pump shaft
and casing, etc,
@f ,re luserey 2€1 Hydr. Valves, Aclualorc & acc€ss

C) According lo the ahape contlguralion :

. O-ring, quad-ring, T-dng, v-ring, U-cap, Hat ring et..

a
o o

l
Pirlor cup 3..1 U{up scrl Piston T-.c.I Rod T-..d
ri& 2.4.t
l{!tad!|g used tor t€ala :

Poly-Teka-tr'luom-Ethylere (P$'E) and Poly-Urettrane(PlD

ensur€ oaximum durability aad Prformance wittr nininum
Eaint€nance. Othe! materials comeonly used are rubber, leather,
Fiber Teflon, plastic et .
U-cup eeals arc used for
1. PistoDE snd pistoD rods ofcylinders
2. Pistoas aDd rods ofaccumulators
3. Pistons ofpumpe

2.4.2 Functions ol Seals :

9m12
O. Whai a.e tho varioug tuncllons ol soals? wdlg the types ol
seals usod.
w-2u3
O. Wrile any four func-tions ol hyd.aulic seals.
g2lr14
O. Give th€ funclions of hydraulic 6sals.
w-2arr4

L O. List the lunction ol Oilseal

ffi,." {us"-.) 2-82 Hydr. Valves, Acluators & access.

Maitr function of Besl ia to stop leak ge offluid, to stop loss of

oil utrder pressure to the surroundings, t retain tlle oil
under pressure withir the systeE.
Other fuactioDs are :

To Leep duat, dirt and contamioant3 away from the fluid, tD

avoid them eDt€rilrg into the oil under pr€ssure from outside.
To avoid powe! los3, and to ioprcve efEcieDcy of the s]Btem.

To keep the surroundingr clean (in case of hydnulic

slatem8).
To avoid slippery floor,dirty surroundiagE, accideDtu and fir€
hazardB (in case of hydlaulic syBtems).

2.4.3 Causes tor Failure o, Seals

w-2ltr1
O. Stale any foul reasons ol failure ol hydraulic seals.

Following are the rcasons for failure ofhy<lraulic seals

. Exccssive heat
. Exce$ive load
. Excessive clearance
. Excesgive pressure
. Improper ittiag
. Improper groove geometiy
. Improp€r filter rating
. Cotrtaminationoflluid
. Idle storage ofs€als
. Age hadening
. AbrasioD
@ ,r. (us"r.) 2{i} Hyd r. Vafu6s, Acbators & access.

2.5 Fllter in Hydraulic System :

s-2012
O. What is oil filter : What is its tunction? List tho tyPs ot filters.
w-*tt2
O. What is tundion of filto, How filters are dassilied? Name any
lour advantages of bypass filter.
w-ax3
O. Give the classiticalion of fil'tors used in hydraulic systom.
Explain ono ol them.
Dust in the working oil u.oder pressure q€ates a lot of
probleEs in the system. It incrcases friciion betweeo the
moving parts; herce theie $ill be wear atrd tear of Part€ and
loss of ederg/ i[ the forB of heat.
The dust forms vanish or get atrd choke up the ports atrd
vei-nB in tie system, which 6eat€s disturbance to the flo$ of
fluid. It incr€as€s tate of oxidatioa of oil. It coEodes the
metgllic surfaces.
The troubles due to dust in the worLhg oil under preesure
are couDtless. Hence the dust has to be rcDoved 6rst and
clean workiDg oil uDder pressure should be supPlied to tie
Br€tem.
2.5.1 Cl$3flcatlon FllteB :
A) Ct ssificstio! occordinS to fuDction
1. Surface type
2. Edgp type
3. Depth tlTe
B) Clasgification accordlng to constructlot!
1. By-pass tyF 6lter
2. Full flow filtrr
3. Proportional Oow 6ltcr
4. IDdicstor type filter
EP,r, (rs"r.) 2-A4 Hydr. Valves, Actualors I access

2-5.2 Surlace Type Filter :

This is also called screen

frlter. In surlace t}?e filter,
the solid impurities are
screened and retained on the
surface of fiIter.
lil
Filter elements are meshes of
metal wires, woven cloth o{
metal wires or yarn etc.
Wirc meshes of different sizes
are used. lhese filteN can be
cleaned and reused. Fig. 2.5.1

2.5.3 Edge Type Fllter

In this t,,p€ of filter, the solid

impurities are happed at
edges of the plates which are
arlaDged parallel to each
other with negligible
clearness between them.

Different twes are disk type,

ribbon tru€, plated type.
These filters can be cleaned
and reused.
Disk t}?e filter is rated at
Dra n plug
98% removal ofparticles from
40 to 125U, Ribbon tlpe from
FiE 2.s-2
25 to 500p.

I
Ef ,r, (rsur.) 2-aS Hydr. Valves, Actuato6 & accoss

2.5.4 Oepth Type Filter :

. In deptl type filters, the solid

impuities entDr into the
frlter element to celtain
deptl atrd trapped there.
. The filter element are hade
of such aE sintpred
'rlaterials
mat2rials po$dels, sbt€red
cerarlic powders, natural aDd
syntletic fib€r3, yarn, cottotr

. Filt€r elemedt of sint€red

powders csn be cleaned t
exteDt by back washing. But
other types, which are Iig. 25J
mentioned above, catrnot be
rcus€d,

2.5.5 By- P.ss Type Fltter :

. It has a spring-loaded by-pass
valve in tetween iDlet and
outlet port.
. Whenever the frlter elemeDt
is chocked up to a gr€ater
extcnt, thi-s v6.[ve opens to
make direct connectiotrs from
inlet to outlet.
. Thue it safeguardr the filtcr
elemert against aDy damage
due to high-pr€ssuie Fig. 2.5,4
difreretrce.
E ,r" (r""r.) 2-86, Hydr. Valves, Actuators & acc€ss.

2.5.6 Full Flow Filter:

As the Dame implies, the firll

flow of oil under pressure is
filt2red.
The oil under pre8sure has to $ l$
flow through the filter elemeDt
completely, and the entire oil is
filtcred and clear oil is coming
out ofthe filt€r.
Fig. 2.55

2.5.7 ProportionalFilter
IB proportiotral filtcr, a
portion of the oil under
pressure oDly passes
tbrough filtcr elemeDt.

R€st of the vollrme of oil

under prcssure passes
diEctly utrfiltcred thmugh t1
the veatuii.
tl
I'his is needed if the
discharge through filtcr
elemetrt is less, that is, the
6lt€r elemetrt is very fine,
and the syst€m need more
discharge. Fig, 25.6
@f ,r" (rserE) 2-A7 Hydr Valves. Aclualors & access

2,5.8 FlltrationMelhods:
Following are the ditrercnt methods of placing the filtc.s

(1) lnlet fitters or strainers - prolecls the pump

Here the filt€r is placed

E
at inlet of the suction
pipe of pump- Hence the
solid ihpuiities
trapped at the begiDning
it€elf, and the pump and
Bystem componetrta aie
pmtDcted froE dust and
solid impurities. Fig.2.5.1

(2) Pr@sure llns tillers - prolecta the syatem

compononts
Here the filt€r is ptaced at outlet of pump. Hence tlte solid
iDpurities are trapped aDd r€moved from the oil under
prssue conoiDg out of the Pump. Herce the s,'steE
components aie prot€c'ted from dust and solid impurities.

gE

Fig.2.5.E
ffi,r" (r,rsare) 2'84 Hydr. Valves, Actuators & access

(3) Return llne lllters - keeps contamination away trom

leaervoh
Here the fiIter is placed at E
9
outlet of system, which is
in the retum line to t}le e
reservoir. Hence, the solid
impurities are trapped
snd removed from the oil
under pressure entering
the reservoir.
Hence oil under pressure
in the reservoir is fiee
l'ig. 2.5.9
from contaminants.
(4) Ofi line tilters - a separate independent filtration
cl.cuit
B D
We can use a sepatate
independent line
containing a pump ard
filt€r, which is operated
aftcr scheduled time
p€riod of operation of
syst€m, to rtemove the
contaminants and to
clean the fluid.

Fig.2.5.10

Function required Ope{ Close

To clean the oil in rcservoir A&B C&D
To clean oil in barrel (drum) C&D A&B
To cha4e (fill) oil into reservoir B&C A&C
To drain out reservoir A&D B&C
El ,r" (rs"r.) 2-89 Hydr. Valves, Acluaiors & access

2.6 HydraulicReservoirs:
Oil reservoir k a storage t5trk to store the oil. It is placed at
a lower level so that, oil flows back in t it by glayity when the
Byst€m fu Bwitched of.

Funcuon! ol oll rglervolr :

. To store suftcient aaouat ofhydraulic oil,

. To cml the hot retur:n oil, and dissipat2s heat to the
surroundiDgs,
. To allow conteminations to settle doryn to renove them,
. To allow air bubbtres to coDe up aDd to vent them out,
. To separate out watcr cootai[ed i[ oil by demulaification,
. To give positive suction pressure to the pump at inlet,
. To mate a coDveDieDt mountiDg place foa pump, Eotor, ard
valves.

S'ghl gla8s Orain plug

Fis. 2.6,1
ffi,r" rr"ur.r 2-90 H Valves, Actuatorc & access.

Parts o, oil reservoir :

I Suficieutly bi8 t6DlI : TaIrk should contain sufficient
aEount of oil to cool the hot rcturl oil.
Thz tink Dolunv should be 2 to 4 tit les thz pump flau in
gprn. If pump delivery is 25-gpm, the resewoir should be of
50 to 75 gallon 3ira.
Bacle platc : It is a vertical plat€ provided between pump
inlet and retuin li.oe. It Bakes the hot return oil to travel a
loDgest possible distrnce in the r€servoir beforc entcring int,
the pump idet. It avoid-s the hot return oil dir€ctly entcring
intD the pump.
During t}is travel oil cools down, contaminants gets settled
down, air bubbles x'ill be rcmoved, snd watrr is separatcd
out,
3 Filler.br.eather cep : It is used for fitling new oil i,lto the
rcservoir. It also serves the purpose of s.tlowirg air to
breathe in and out.

1. Sigtt gles€: lt is used to see the tevel ofoil ia the taDk. If

tevel is low, then fregh oil Bhould be added.

Drai[ plug : It is necessary for rtemovi-trg the uaed oil &om

tlre rcseroir during oil chaDg€. For the purpo€e of easy
removal of oil, tank bottom b stroped down topard8 the drain
plug.

6. Clorn out door : It is oecessary fo! cleaniog tle re-servoi'

inside. Proper eesle and gaekete arc us€d for closing this
door.

Streiner : It is a course frlter 6ttcd to the inlet of suction

pipe; it does not allow contamioation8 to enter into the
pump.
181 re 2-91 Hydr. Valv€s, Actuators & acce:is

2.7 HydraulicAccumulator:
9Nt1
O. Why accumulato6 are used in hydraulic circuit? Explain an
one type ol actumulalor with neat skelch.
*2tt13
Cl. Enlist any lour advantages and disactvantagos ol gas loaded
a@umulalot.
w-2r13
O. Explain lhe tunclion of acGrmulaio6 in hydraulic circut- Dra,rv
symbol ol spring toaded accumulator.
s-N14
O. What is an accumulalof? Why accumulalor is necess6ry for
hug€ hydraulic presses.
w-2014
O. List lhe tu.ction ol A@umulalor
A hydrsulic accu&ulator is a rcs€rvoir taDk which
. Collects and storcs the oil under high pressure during idle
runniDg of pump.
. And releaseB the high prcssure oil to tie syst€m when
needed.
Accumulator has s€veral otier fimctioD-s such as
. To work as ghock absort)€r
. To provide oil make-up itr a closed cfucuit.
. To competrsate for lealsge iD the systsm
. To worL as aD emergencJ. source ofpower
. To work as a transfer barrier to separate oil from other
impurities
MEln purpoas ol accumulalor :
. To seve power duri[g idle !'eriod
. To avoid over-heating of oil
If the hy&aulic circuit has large cylinder, speed is high &nd
idle period b more,
Then by usitrg accumulator, we caa replace large pump by a
small pump, save power during idle period and avoid overheatio:,
ofoil.
l,lPl rrp ru SBTE) 2-92 Hydr. Vatues, Acluators & acc6ss.

2.7.1 Classilicatlon of Accumulators :

'L Dead weighl accumulator :

It has a vertical cylitrder inside which a piston is assembled.

The piston is loaded by {eights. The weight may be balast cast
ircn or concrete steel etc.

fwl

F.om pump To ryst€m

fiB.2.7.1

2, Spllng loadod accumulator :

The piston inside the accumulator is spring loaded. lhe

spring gets compresged as the liquid fills itr the cylj"oder. 'Wtrenever
the system needs oil, the oil flovrs to the system due to spring force.

Flom Pump To qstorr

riB 2-7.2

3, Ah or gas loaded accumulalor :

There are two t5Eres oI air of gas

loaded accumulator,
namely, Non-separator type and sepamtor t}?e.

8) Non-separator type :

In this t}?e of accumulstor, the compressed gas is not

separated from hydraulic oil.
EEf ,rp usere) 2-93 Hydr. Valves, Aclualors & acc.,ss.

b) Sepa.sror rypo :
In this tlTe of accumulat r, the comFessed gas is separated
fiom hy&sulic oil using a pfuton, a diaphragm, or a bladder.

From pump To systgm

I1A.2.73

2.7.2 Accumulator Clrcuit :

H
oAc

il)x{F
ob

FiB.2.7.4

lhe above Fig. 2.7.,1 shows a hydraulic pl€ss cLruit ia which

atr accumulator i.s us€d to Eave the power aDd to avoid overheating
ofoil.
@l ,r" tr"rt.) 2-94 Hydr. Valves, Aclualors & access.

Problem specilication :

1. Power consumption is mor€

2. Oil is overheating
causes (Reasons) :

1. Cylinder is l6rge : Iarge cylinder requires large volume

of oil to exterd and rctract. For t}lis,
a big pump of high dischargp is
needed. Hence, power rcquired to
run the pump is more.
2. Idle period is mor€ : During idle time, the large volume
of oil which is pumped by the pump
flows back to the resewoir
continuouBiy at high pre$ure
though the small rcstriction of
pressure relief valve.
Ihe power giveo to the pudrp is
not utilized in doing any work;
hence, it is lost ir! overh€ating
the oil.
What we can do to solve this Problem?
. We can use an accumulator of capacity more than "tvi'ice
the volume of the cylinder".
Volume of accumulator = 2 x volume of cylitrder
. we can replace the big puEp by a small pump of
discharge equal to "twice the volume of the cvlinder/idle

Accumulator volume
Discharge of small pump = Idle time
2 x volume ofcvlinder
- I.tle time
ffi,r" (rsur.) 2-95 Hydr. valves, Aciuators & access

What we achlsvo by doing 8o?

1. As small purnp is used, power required to rurl the PumP is
very less. So, there is considorsble saving ia Power.
Running coBt of the s]'stem is reduced.
2. During idle priod, oil pumped by the Pump 6113 t}re
accuEulat r. Oil flow bsck to the reservoir at brgh Pressune
is avoided. and overheatilg of oil doee not occur.
3. Cost of small pump is far lesser than that of big pump. So,
initiel cost of the s]'stco is reduced.
2.8 lntensifiers or Pressure Boosters :

Int€Dsfier (boost€.) is used to i.ucr€ase the pl€ssure ofoil.

It consists of two cylinders, namely, inPut cylinder and
output cylinder.
lte diamet r of input cylioder is Dore than the aham€t€r of
output cytinder.
L€t, Ar = area ofinput cyliDder
A2 = area ofoutput cylitrder
p1 = pressure ofoil supplied t the ht€n8ifier
p = pressure of oil delivered by intsnsifier
When oil under pressu.rc pr is supplied to iDPut cylinder, tie
pressure is magnified by the intensification factor A,/Ao and
oil is deliver€d with magnified preesure P2 from the output
cylinder.
prxA,
Pressure of oil delivered = P, = -:6-
If Fr = packing friction in iaput cylindei
F2 = packing frictioa in output cyliade!,
(Pr x Ar) -Fr - Fz
Then, Pressure ofoil delivered = P2 =
@f (*""r.) 2'96 Hydr. Valvos, Acluators & acc€ss.
'r,
2.8.1 Single Acting Booster:
Single actiag prcssur€ boostel is operated by 3/2 directioo
control valve,

In first position of spool of 3/2 DCV, oil under pFessure pr

flows t A port of the input cylinder, pirton moves
downwards, and oil uader intensified pressure p:) is delivered
iiom Q port ofoutput cylinder.
When the spool of 3i/2 DCV is sbifted to the second position,
piBton moves upwads due to spring folce, and oil flows out
from the A port of iDput cylinder. During this shoke, oil is
sucked into the output cylinder tbrough port P.

T
3D OCV

o
Oulpur

Fis.2.E.r

2.8.2 Double Actlng Booster :

. Double acting pressure booster is operated by 4/2 dircction

control valve.
. ln first position oI spool of 42 DCV, oil under pressure pr
flows to A port of the input cylinder, piston moves
downwards, and oil under int€nsified pressure p2 is delivered
from Q1 port ofoutput cylinder.
llYl IFP (MSBTE) 2-97 Hydr. valves, Acluetors & access.

When the spool of 4/2 DCV is shified to the second position,

oil under pressue pr flows to B port oI the input cylinder,
piston moves upwards, and oil under int€Dsfied plcssure p,
is delivered from Q2 port ofoutput cylinder.

B o2

o1

Fle.2.a2
Appllcation! ot prs&Bu.e l onalliers :

. Burst pr€ssure testing 6achioe,

. curing Pie33e6,
. riveting machine,
. high pre$ure damping devices et
Advantagss ol pisssuls lntsnllflsra :

o Expenaive hfuh pressure pumps can be replaced by sEaller

pumP8.
. Much highei Eessure cen be obtained, compared t pumps.
. Overheating of oil is avoided.
r Inside Eitres, electrically op€ratd pumFs cannot be used
due to the dsnger of explosions, air operated pressure
boostcrs csn be employed to obtain high prcssure oil.
ffi,r" (r""r.) 2-98 Hydr. Valves, Aclualorc & access,
2.9 lmportant Examination Ouestions and
Answers
Please refer ebooh for complete solution
Not€ :

1. Ptease dnwnload our free e-bnk for detailzd dnsuers

of fo\ouins qu$tioB.

2.
Nl qwstians & Ansuers couer the complzte

2.1 C@trol VrlT.r :

Q. 1 Statc difrerent types (atry 4) of pt€ssure control
valves with their appticatioDs. lsecri,on 2.I.31 ($ll)
Q.2 with a neat 6k€tc.h, explain ttre futrctioning of simple
pressue r€liefvslve. asectian 2,1.3.11 ($f4)
OR
Q. 2 Wtst is the function of plessure reliefvalve ? Where
it is located ? Sketah dircct operating prcssure rclief
v6lve. [Section 2.1,3.1] (W-12)
Q.3 Drasr and explaiD working of plessure reduciog
Ysive. tsectian 2.1.3,31 ($U)
OR
Q.3 Explain with Deat sketch lvorkioS of <lirectly
operqted pr€ssure.eduoDg vslve. (W-lf )
ISectian 2.1.3.3]
Q.4 Give the coBparisotr between prcssure relief valve
atrd pr€ssure reducrng r,al,le. [Section 2.1.3.4] (W-lll
OR
Q.4 Difieretrtiate betweeE prcssute rclief valve 6nd
prcssure reducitrg valve with respect to its fisction
synbol, BorDal position aDd op€rated elemetrt.
[Sectian 2.1.3.4] (W-l,f)
Q.5 Give cooparisou htween preaaure elief valve and
unloqdiDa valve. Isecr.oz 2.I.3.6J
Q.6 Explai! working of directly operated check valve
($f2)
with neat stetch. fsection 2.1.4.11
Kfl rFP ( MSBTE) 2-99 Hydr. Valves, Actualors & access

OB
Q.6 State the firnction of check valve in
hvdraulic
circ\itlsectinn 2.1.4.1,/ (W-13)
Q.7 Explain the working of rotary spool type valve with
neat skeLhlsection 2.1.4.21 (913)
Q.8 Draw a neat sket h ofr2 D.C. valve. Erplain its
wotk}J:z.lsectian 2.1.4.31 (912' W'13)
OB
Q.8 Sketah the two positions of sliding spool twe 3/2
DCV atrd explain in brief. [Section 2.1.4.3] (91'l)
Q.9 Draw a skekh of nor:Elal and actuated positioDs oI
4|?DCY. lsectinn 2.1.4.4] (9rl)
OR
Q.e SLet h the two positions of,otary spool tyPe 4/2 DCv
and explain in brief. /Section 2.1.4.41 (Sf'f)
Q. 10 Explain 4 way 3 position direction confol valve used
in hydraulic syst€o \rith sket.h. (911)
ISection 2.1.4.51
Q. 11 Exptain why 4/2 DCV is prcferred for hydraulic
systpms and 52 DCV pneuEEtic system.
tsection 2.1.4.61 (914)
Q. 12 wh,t i6 flow contml valve'l tsection 2.1.51 ($11)
Q. 13 Explain noa pressure compensated flow contlol
va]Lve. lSection 2.1.5.21 ($11)
Q. 14 what i6 pressure compeDsatd flow control valve ?
How does pressure compensation tskes place
tsection 2.1.5.41 (w-r2)
OR
Q. 14 Exptain pressure compensat€d flow control valve
with neat sketch.lsection 2.1.5 41 (W-r1' W-13)
Q. 15 Explain with neat skekh the working of time delay
valve. I section 2.1.6.11 (w-rr)
Q. 16 Explain with neat sketch, construction of pilot
operatedcheckvalve.lsection2.I.6.4l (S-13)
OR
 rFP (MS8rE) 2-100 r. Valves, Actralors & accoss

Q. 16 Erptain opposing loed and over runnitrg load

coasideriag the case of &iftirg ad lowenDA the
w eighl. tsection 2. 1.6.11
Q. 17 CoDpsrisoD betwee! "poppet (seat) type valve" aad
'spool type valve". Isection 2.1.6.51
A.a ...trr,torr h Eydrauuc Sy.t D
Q. I What sre actuators ? How tiey ar€ classfied ? Draw
aud lalel a double acting hydraufic cyliader. (W-f2)
OR
Q. 1 Give the detsiled classification ofhydraulic
[Secti,.n 2.2..U ($f8, &14 W-1,1)
^&natar8.
Q.2 Draw labelled diagram of any one actuator us€d io
hydr.aulic systcB. Explain its coDstructiotr and
working. [Sectian 2.2.2]
Q.3 Draw a figur€ of actual coEt&ction of siBgle acthA
eir rylinder and label it. [Section 2.2.2.2(N] (Y-tal
Q.4 Sfetch and label lhe diegram of pneumatic
diaphragmcylinder.ISecrian2.2-2.3(A)l (W.f8)
Q. 5 Wbat is tatrdem cylider ? Exptain with no-t sketah.
Draw symbol of it. lslection 2.2.2.3(Ol (W.f g)
Q. 6 Draw s.nd explain the working oftelescopic cylinder.
tSectian2.2.2.3(E)l (S11, W-rl, &12., W-rg)
OB
Q. 6 ETIain tclscopic cylirder lrith sketah.
[&ction 2.2.2.3@)] (W.1{)
Q.7 Ealist ary four tJ.pes of pneuDatic cylinder
gro\tntiryB. [Sectian 2.2.2.4] ($18)
Q. 8 Stat€ ttre differert types of air motors. Explain s.oy
o\e. [Section 2.2.3] (gu, W-11)
Q. 9 Explain gear motor x.ith neat sket h.
tSection 2.2.3.2(Nl (Sf2)
Q. 10 With a neat sketch, explaiD conetruction alld
working ofvane tjrpe air motor. (W.12)
ISection 2.2.3.2@)]
Q. 11 Draw a [eat sletch and explaitr worting radial
pistotr tyPe hydraulic motm. tSectinn 2.2.3.2(I)l(W-tll
l( I rre tMseret 2-101 Hydr valves. Aclualors E access.
g.A Plpo trrtotLb for tLydrsullc .yttsEB r,[d Pnoumatlo
.yctoD.
Q. 1 Enlist vsrious materials used for hydraulic Pipes.
($ls)
OR
Q. 1 How hydraulic pipes are classified ? (W-13, 9rA)
OR
Q. 1 what are tie various t,pes ofhoses used in
pneumatic system. (S'f3)
Q.2 Which mat€riale are used for layels of hoses in
pneumatic system, Draw cross section of Pneumatic
}:lose pirP'. tsection 2.3.11 (W-rr)
OR
Q. 2 Draw constructional details of pneumatic hose. Why
hose is required iD pneumatic ciicurts.
tSecti.on 2.3.11
(W-r3)
Q.3 Write ary four tip6 lor good piping in pneumatic
aysteltris. [Section 2.3.2] 0-r3)
OR
Q. 3 How good piping system is desiSned. Stat€ their tiPs.
tsection 2.3.21 (Sl3)
OR
Q. 3 What are the requiremetrts ofBpod oil under
pressure power plumbiag? [Section 2.3 2] (912)
Q.4 Explah (1) Standa pipe (2) Extra stmng piPe.
(Sl2)
t9ection 2.3.41
Q.5 Name any eight pipe and tube 6ttings. Write tleir
function id brief.lsecti,on 2.3.6/ (W-f2)
2.a S6als lD Eydraulo AytbE
Q. I Sketrh the cup seal, and writP its applicatioDs.
fsection 2.4.1] (S-19)
OR
Q. 1 Differentiate b€tweeB static seal and dynarnic seal.
[Section 2.4.1] (Sr4)
Eff,r" usere) 2-102 Hydr. Valves, Actuators & access.

Q. 2 What are the various firnctions of seals ? Write the

tl,pes of seals used. lsectian 2.4.21 (912)
OB
Q. 2 Write any four functions ofhydraulic seals.
tsection2.4.2l (W-13,9r4, w-r,r)
Q. 3 Stat€ any four reasons offailure ofhy&aulic seals.
[SectiDn2.4.3] (W-lr)
C.5 trUtsr h EydnuUc f,y.t6m
Q. I What is oil frIter : What is its tunction ? List the
typ€s offilt€rs. (S.12)
OB
Q. 1 What is tulction offilter ? how 6It€N are classified ?
Name sny four advantages ofby.trrass 6lter. (W-f2)
OR
Q. 1 Give the classiicatior of filters used in hydEulic
system. Explain any one ofthem. (W-13)
2.7 Eydr.ultc AoaumBlrtor (tor hydrsullc ayst r!t.3)
Q. 1 Why accumulators sre used in hydraulic cirarit ?
Explain any one t}T,e of accumulator with treat
sLetch. (S"11)
OR
Q. I EDlist any four advantages and disadvantsges ofgas
loaded accumulator. (913)
OR
Q. 1 Dxplain the finction of accumulators in hydraulic
cirEuit. Draw sFnbol of spring loaded accumulator.
(w-13, W.1d)
OR
Q. I What is an accumulator ? Why accumulator is
necessary for huSe hydraulic pr€sses. (S.1,o

EDO
Chapter 3

Oil Hydraulic Circuits

Syllabu3 :

. 't|eter in', 'Meter out', 'Bleed off', Unloading, two

cylinder synchronlzing, regenerative,
counterbalance, dual pump unloading circuits'
. Sequencing circuit - time dependent and pressure
dependent.
. Oil hydraulic circuits for milling machine, shaper
machine.
lB ,rp (usare) 3-2 Oil Hydrsutic Circuits

3.1 Operating SAC usin sU2DCv:

92013
O. Stale the use ot DCV showlng ils posilion in tho circuit.

For op€ratiDg SAC, we use g/2 DCV.

3/2 DCV has thtee ports namely iolet port ?., tank port .p
a]ld cyliDder port "A. .

It has two positioos ofits spool

Iatatlt

rtg 3.l.t
In first position of spool of 3/2 DCV, oil under preseure flows
fiom P to A and T is ctos€d. Henc€ the piston of SAC ext nds.
In second positioo of spool of &2 DCV, oil under pessure
flows fiom A to T and P is closed. Hence the pieton of SAC
 3-3 oil Circuils

3.2 Operati ng Unidirectional Motor using 3/2 DCV :

U iiectiooal motor csn be opelatd by 3/2 Dircction

Control valve.

3/2 DCV has ttEee ports na6ely inlet port "P', tank port "T'
and cylinder port 'A".

It has two positionB of its spool.

118.3.2.1

In 6rst position ofspool of3/2 DCV, oil uoder Pressure flows

ftom P to A aod T is ctosed. Hence the shaft of the motor
ru,1a.

Itr second positiotr of spool of 3/2 DCV, oil under presaue

flowe from A to T and P is closed. Hence the motor stoP6.
ffirre (MSBTE) 3-4 OilHydrautic Circuils

3.3 Operating DAC usi ng /u2 Dcv :

For operatiog DAC, $/e use 42IXt1.

4/2 DCV has {our ports namely inlet port "p", tant port -f,
cylinder port "A.' and cylinder port "B".
It has two positions of its spool.

Fig.3.-1.1

In frrst position of spool of 4/2 DCV, oil under pressure flor rs

from P to A and B to T. Hence t}le piston ofDAC ext nds.

In second position spool of 4/2 DCV, oil under prcssure floy{s

fmmPt B and AtoT. Herce the piston ofDAC retracts.
m IFP (MSBTE) 3-5 Oil Hy&aulic Circuils

3.4 Two SAC using One /V2 DCV :

,!2 DCV has two cylinde, Ports naaelv, cylbder port "A'
aad cylinder port "B". If ther€ are ts/o shgle actiDg cvlhders
we can coDaect each port to each SAC, so that, while one ie
exteDding th€ other will be retracting.
4/2 DCV has two positions of its spool.

a ,q

B
#
T

n& 3.41
In 6rst position of sPool of 4/2 DCV, oil under pressure flowa
fiom P to A and B to T. IIence the cylinder-l extends strd
cylinder-2 rctrscts.
I[ second position spool of 4/2 DCv, oil under pr€ssure llows
from P to B and A to T Hence the cvlirder-2 exteDds snd
cylindor-1 rctracte.
@l ,r" (r"" 3-6 OilHydraulic Circuirs

3.5 Operating On ly One SAC usi ng a 4r2 DCV :

We know that 3/2 DCV is required to operatc a SAC. But, if

you donl have 3/2 DCV. and insread, you have a {,r2 DCV,
then. no problem, you can use it by closina any one of its
cylrnder ports.
C2-DCV hae tvvo cylinder ports DarDety, cytiDder port .A-
and cytinder port "8". If there is oDty one SAC, then connect
any oDe ofthe cylinder ports to the SAC, a.nd plus (clos€) the
other clinder port. Now the q2 DCy acr,s as 3/2 DCV
because out of 4 ports one is plugged add only g alte
remaDrng.
4/2 DCV has two positions of its spool

# B

II

r.ig.3s.l
IB first position of spool of 4,2 DCV, oil under preseure flows
fiom P to A and B & T are closed. Hence the SAC extends.
IIr second position spool of 4/2 DCV, oil under pressrue flowe
fiom A to T and B & P aie closed. Hence the SAC rctracts.
l98l trp 3-7 Oal Hydraulic Circuils

3.6 Operat ing DAC using IV3 DCV :

. We use,US DCV t opelat€ DAC, t ext€ad, retmct ard to

stop atrfrher€ in the middle.
. this valve ha! four ports namely idet port "P', tank port
"T", cylinder ports "A arrd "B".
. It has tiree positions ofits spool.
. Itr 6lst position of spool of 4/2 DCV, oil under pressure llows
from P to A and B to T. Hetrce the piston ofDAC extends.
. Id second posihon apool of 4/2 DCV, oil under Pressur flox's
fromPt B and A to T. HeDce the pistoD of DAC retracts.

c
E
B

ns.3.6.1

In Eiddle position of the spool, the cvtinder Ports are closed.

Hetrce the cylinder stops.
EEf,." (u""r.) 3,8 Oil Hydraulic Circuils

o In the above example,,4*l tsndeD cetrtE mid position DCV is

used.
. In it€ mid position, Port A and port B are cloeed, so that the
cylinder fu locked, cytinder vrill not move due to over-running
load.
. Port P i-s coDnect€d to prt T, which allows free flow of oil
back to tank with no pressul€. It avoids over-heatiDg of oil
and saves power during idle period of the 6yst€8.
Not6 :

ln pneumatic ciEuits, li,e use only closed centrr twe,

because the port 'I- is opeo to atmosphere. We cant us€
tandem center or open center where, compEssed air will be
loBt to atmospherc.

But in hydraulic circuits, the center t,.pe is chosen a.s per the
applicatiotr.
There are maoy ilifrerent t,pe6 of Eid positions of ,U3 DCV
namely closed center, open center, taodem ceDter,
Egenemtive type center, flush t,?e center, alrd otier€.
All are having specfic applications. Functioning of circuit
should be studied and accordingly the ceDtr€ tf,pe ghould be
chosen.
 3-9 Oil Hydraulic Carcuits

3.7 OPeratin g BFdi rectional Molor usin 4/3 DCV :

Fk 3.7.1

The above Fig. 3.7 1 show6 a hvdraulic circuit to operst€ bi-

d.ircctional motor using a tandem centclUS DCV

In 6rst positiotr of 4/3 DCv, oil flows from P to A and B to T'

Hetrc\e the motor ruDs in clockwis€ dircctioB'

In second position oil flows froa P to B and A to T'

rVB DCV

Hence the motor nrns in alttidockwis€ direction'

By operating the flow coDtrol valve, we can vary the flow

rat€ of oil and thereby we can contml the spe€d ofthe motor'

In tandem center typ€ mid position 4A DCV, port A aod B

are clo€ed. Port P i3 connectcd to Port T TheEfore oil from
the ciftuit flows back to reservoir tsnk Thi-6 prevetrts
coEtinuous flow of high_presstrre oil to leservot though t'Irc
small psssaS€ of pressure relief valve, and thus avoids
overheatitrg ofoil.
 IFP iMS 3-10 oit Circuits

3.8 Two Hand Op€ration Circuit:

This is a safety chcuit to safe-guard the hands of the

operator. Here, the operator is msde to engage both of his
hands in operating the valves for making the DAC to extend.
There wont be any third hand teft in betweeD the punch and
die, thus, it avoids the chance of accident or injury to the
hands of the op€rator.
It is "AND" logic circuit. Definition of this logic is "output is
preBent only when both input-A ss well as input-B are

Here, output means ext€nsion of DAC. Input-A means

actuation ofvalve-1. Itrput-B means actuation of valve-2.
3.8.1 Two Hand Operation ol SAC Using Two 3/2 Valves :

Actually, one 3/2 DCV is sufrcieot just to operat2 s SAC. But

for safety of operat ls hands, the safety circuit coDsists of
two 3,2 valves.
Operator hss to operat€ both of these valves together, then
oDly the DAC extends.

T
!l
M

['ig. ].8.1
@ IFP (MSBTE) 3-11 Oil Hydraulic CircuIs

I1te circuit contains two NC 312 valves. NC m€ans, "normally

clos€d'. In normal position, the inlet port "P" is closed and
cylhder port "A" is connect€d to tank port ry'
These two valves are contrect€d in series, thst is, the outlet
port of first valve is connect€d to inlet port of second valve'
When both of thes€ vatves are pressed t gether, oil under
pressure flows ta SAC and tlle SAC ext€nds-

3.A.2 Two Hand Oporation of SAC Uslng Twln Proaaure

valve :
Shuttle valve has AND logic functiotr. If oil unde' pressu'e is
supplied through both of the two iDlet po.ts, inlet port A or
inlet port B, thetr only there will be supply from the outlet
Port c.
Circuit coDsists of two NC 3i/2 valves, valve_l and valve-2'
T'he outlet of valve-l is connected to inlet'A and that of
valve-2 is connected to iDlet_B. The outlet_C oftwin pre$ur€
valve is coDnectcd to SAC.
Whetr both of these vatves are Pressd together, oil under
pressurc flows to SAC and the SAC extetrds'

I
$
T

Fis.3.8.2
@) tFp t MSBTE) 3-'12 OilHydraulic Circuits

3.8.3 Two Hand Operation ol DAC Uslng Two 3/2

Valves:
As we know, a W DCrl has one cylindel port, where the
DAC has two ports. Hence for operating DAC using 3il2 DCV,
we Deed two 3Y2 valves.
Connect one valve to one f'ort of cylinder and the other valve
to othe, port.
Itr Fig. 3.8.3, valve-l is coDnected to cap end port "C" and
valve-2 is to md end port'R".

Fis.333
Valve-l is NC valve, that is, it is norlllally closed typ€ valve.
ln normal position, the inlet port "P' is closed and cylinder
port "A" is connectcd to tank port 'T'.
Valve-2 is NO valve, that is, it is normally open t),pe valve.
Ia normal position, the inlet port "P is connected to ryIinder
port "B", tank port 'I- is closed.
In normal position of these two valves,
o Oil under pressue flows to the cylinder at rcd etrd port
"8" through valve,2, comes out from cap end port "C"
through valve-l atrd flows to the tank. Hence. DAC
rctracts in normal positioE.
w IFP (MSBTE) 3-13 Oil Hydraulic Circuiis

For extcnditrS the cylinde!, operator has to preEs both the

two valves together. BY doing so,
o Oil uncler Pressure floll's tD the cylinder at cap end port
"C" ttrrcugh valve_l, comes out frorD rod end port "n"
through valve-2 atrd flows to the tgnk Hence, DAC
extenilB

3.9 Ope rating DAC using 5/2 DCV:

For op€rating DAC, we csn use t2 DCV-

,2 DCV has frve ports namely inlet port "P', cylinder port
"A" and cylinder Port "B" tank port'T1", tank port'T2"'
5/2 DCV has two Positiom of its spool
I
I
c

T1 t2

fig.3.9.l
In frrst positio[ of spool of V2 DCV, oil under pnessure flows
from P to A and B to T2. Hence the pistoE of DAC ext'nds'
ID second position spoot of ,2
DCV, oil under Pr€ssure flows
fromPtoBatrdAtoTl Hence the piston olDAC rehacts'
 MSBTE 3-14 oit raulic circuits

3.10 Automatic Continuous Operation of DAC:

We can ue€ either of the follofing two tj,p€s of circuits for

obtaining continuous reciprccation of pistoD of double acting
cylinder
o By using limit swit hes and double solenoid 4/2 DCV.
o By using limit valves and double pilot 4/2 DCV.
By adjusting the position of limit switches or limit valves, we
can adjust the length and position of stroke of the cylinder.
Hence these circuits are also called "strok6 control
circuits".
3.10.1 By using Limit Switches and Doubte Solenoid 4/2
DCV :

c
h
LS1
6
L52

sl

Fig.3,l0.l
In this circuit a 4/2 double.solenoid DCV is used.
The!€ are two limit swit hes to operata this 4/2 DCV
ffi ,r" (rs"r.) 3-15 oir Circuils

. Whea a limit switch is pressed, electric curr€nt flows to the

connected soleooid aad hence tle spool of 4/2 DCV shifts to
other position.
. The piston rod, while reciprocating, actuates t}lese limit
swit hes, which intsrtr actust€s 4/2 DCV ThuE automatic
reciprocation ofram is achieved.
. In first position of 4/2 DCV, oil utrder pressure flowB Eom P
to A and B to T. hence the rylinder exten&.
By the end of extension, the cam fitted to piston r'od presses
tlle Iimit switch "IS2".
Hence, electric cuEedt ltows tD soletroid "S2" aDd due to this,
the spool of 4/2 DCV shifts to secoBd Position'
. ID second position,U2 DCV oil under ptessure flows from P
to B ard A to T. hence tlre cvlinder retBcts.
. By the end of retraction, the cam presses the limit swit'h
"rs1".
Hence, electric current flows to solenoid "S1" aDd due to tbis,
the spool of 412 DCV shifts to 6rst po€ition. And the cvcle
continues

3.10.2 By uslng Llmlt Valves and Doublo Pllot /lf2 DCV :

. ID this circuit a 4/2 double-Pilot DCv is used.

. There are two cam operat€d 3/2 DCv which arc caled "limit
valves" to opeBte this 4/2 DCV'
. When a lihit valve is pressed, oil under pressure llows to tlrc
coDne€t€d pilot and hetrce the spool of'U2 DCV shifts to other
po3itioB.
. The pist nrod, while reciprocatinS, sctuates thes€ limit
valves, which htem actuat€s 4/2 DCV.
19 rclMSBTE) 3-16 Oil Hydraulic Circuits

t2 -

s
=
LVI LV2
B

Fi9.3.10.2

ID first positioD of 4/2 DCV, oil uader pressuie flows fiom p

to A and B to T. hence the cylinder extetrds.

By the end of extension, the cam itted to piston rod presses

the limit valve "LVt". Hence, oil under pressur€ flows to
pilot "P1" aBd due to tlis, the spool of 4/2 DCV shifts to
secotrd position.

ID second positioo 4/2 DCV, oil utrder pressuie flows from p

to B and A to T. hence the cylinder rehacts.

By the end of retraction, the caD presses the timit valve

"LV2". Hence, oil under pr€ssure llows to pilot ?2" and due
to thb, the spool of 4./2 DCV shifts to frst position. And the
cycle continues,
 3- t7 oil draulic Circuils

3.11 Speed Control Circuits :

w-21t13
O. How the speed of hydraulic motor is controlled? Explain it with
neat circuit diagram.
w-n 14
O. Comoare meler_in circuit wilh m€leroul circurl wilh respect to
well labelled dlaqram. working. lealures advanlages,
limilations and
Soeed of actuators {cylinders or motors) can be controlled
using flow contml will
Varying the rate of flow of oil
"alves.
vary the 6peed ofthe actuator.
o In meterin circuit, rate of flow of oil is controlled at
inlet ofthe actuator.
o lD moter-out circuit, the rat€ of flow is contmlled at
outlet ofthe actuator.
o In bleed-off circuit, the rate of flow of oil is contrclled
in the by-pass line leading towards the tank (oil
reservoir).
3.11.1 etsr-ln Clrcuit lor DAC :

*24t11
O, Explain with neat skolch the workinq and application of meler
in circuit-
s- 12, W-24r13
O. Oraw and explain meler in circuil.
w-2tt12
O. What is the purpose ol mgter in circuit? Draw tlle met6r in
hydraulc circl.rit lo. regulating lhe spe€d ol piston in cylinder.
9m13
Q. Oraw a circuit diagaam of speed control wh6n pislon move
forward in a .sciprocating hydraulic cylindor.
9m14
O. Sketch and explain meler in hydraulic circuil lo control the
speed of oxtension ol DAC. Explain why m€ter in circl]it is not
for over loads-
in meter-in circuits, the rate of flow of oil going int4 the
cytitrder is controlled by flow contrcl valve. FCV is placed at
iDlet of the cylinder. Cap end port 'C' is inlet for extension
al]d rod eDd port "R" is inlet for retrartion
@f ,., IMSETE) 3-18 Oil Hydraulic Carcuits

I c
c

T T

rig. -l.l l.l i'ie. 3.11.2

Metor.iD circuit for MeteFin cilcuit for
6xtstrrion retraction
ID frst positiotr of 412 DC!, In tust position of 4/2 DCV, oit
oil under pressure flows from under pressure flov{s ftom P to A
P to A and B to T. This flow is aDd B t T. This flow iB through
through flow cootrol valve, check valve. lhis is fiee flow
the fiow is contmlled and Hence the piston extends at
hence piston extends slowly. higher speed, which is not
coDtmlled.
In secood position 4/2 DCV, In second position U2 DCV, oll
oil under pressure flows from utrder pressule llows ftom P to B
PtoBandAtoT. and A to T.
This flow is though check This flow i! through flow control
valve. This is free flow. Hence valve, the flow is contr0lled and
the piston retracts at higher hence piston rehactB slowly.
speed, which i.s not cotrtrolled.
Meter-in conhol is used for oppositrg loeds only.
It canl prcvent rutrnirg away loads, because the rcturn liDe
fiom the cylidder is a fr€e path towards res€rvoir. RunDing
away load will pull the pistotr and pistotr can't r€sist that.
lPf,." qsq1qy 3-19 OilHydraulic Circuils

3.11.2 ltlotor-out Clrcuit lor DAC :

. In meter-out circuits, the rat€ of flow of oil under pressure
comisg out of the cyliqder is conholed by flow contiol valve.
FCv is ptaced at outlet of the cyli-nder.
. Rod end port "R" is outlet for extension and cap end port "C"
is outlet for retraction.
tr

Fig.3.ll.3 ris,3.rl.4
Meter-ut circuit ior Motet-out circrdt for
exteDsion rlatrectior
In first position of 4,/2 DCV, oil In first position of 4/2 DCV, oil
under pr€ssure flows from P to under pressure flows liom P to
A and B to T. This flow is A and B to T. This flow is
through flow cotrtrol valv€, the through check valve. This is
flo$ is controlled and hence free flow. Hence the piston
piston ext€nds slowly. extends at higher speed, which
is not controlled.
Itr second position L/2 DCV, oil In second position 4,/2 DCV, oil
under preseure flows from P to under pressure flows fiom P to
B and A to T. This flow is B and A to T. This flow is
thrcugh check valve. This is fiee through flow control valve, the
flow. HeBce the piston retracts flow is contmlled and hence
at higher speed, which is trot piston rctracts slowly.
contmlled.
ffi IFP (MSBTE) 3-20 OilHydraulic Circuils

. Meter-out cotrtml caE be used fo! both opposiag load as weu

a.s runnitrg rwqy load.

Itcan hold running av{ay loads tEcause therc is FCV at

outlet oI cylhder, which Daintains high-pressure oil under
prBsure at cylinder outlet.

3,11.3 Bleed-ott Clrcult tor DAC :

s-2012
O. Draw bl6ed-0fl hydraulic circuit and label (.
w- 12, W.2013

O. Draw and explain in briel hydrauljc bt6ed ot cjrcuit.

ID bleed-of control circuits, a by-pass line is coDnected to

inlet of cylinder. Cap end port "C" is inlet for extension and
rod eDd port'R' is inlet for rctraction.
A flow coDtrol valve is placed in this bl.pass liDe. This FCV
b)?asses controlled amorrnt of oil to flow back to the
reservoi. Only the remaining amount offlow will flow to the
cylinder. So, by controlling the byaass flow rat€, we control
the flow Iat€ going into the cylinder.
Bleed-ofr cootrol is used for opposing Ioads only. It canl
prevent runnhg away loads. This is because the return line
is a free path tov,,aids the reservoir. Running away toad will
pull the piston and piston cant rcsist that.
The advantaAe of bleed-off circuit is that, it allows cert$in
quantity of oil t flow back to reservoi! thmugh ttre flow
control valve duiitrg idle period. It prevetrts the flow of oil to
Ilow thmugh pressure reliefvalve. Thereby, it reducee loas of
power atrd overheatiag of oil during idle period.
ffi,re l,',tsaTE) 3-21 OilHydraulic Circuils

c -n c

a B

Fig.3.ll.5 l'ig. 3.11.6

Bleed.ofr cir.uit for Bloed-ofi circuit for
e!teasion retractioa
In tust positioD of 4,/2 DCV, oit In fust positiotr ol 4/2 DCV, oil
under pressure flows from P to ulder pressure flows from P to
A and B to T. But this flow A ard B to T. This flow is liee
controlled flow lrcauae a flow. Ttere is no FCV in this
controlled amount of oil is line. Hence the piston extends
released back to tsnk through at high speed, which is not
FCV. Only the remainha contmled.
amount of oil is flowing in to
the cylinder. Piston extends
slowly.
In second positioD 42 DCV oil In secord positioD ,U2 DCV oil
under pressurc flows from P to under pressune flows from P to
B and A to T. This flow is Iiee B and A to T. But this flow
flov{. Therc is no FCV in this contmlled flow because a
Iine. Hence the piston retracts conholled amount of oil is
at high speed, which is not released back to tank thlough
controlled. FCV. Only the remaining ]
amount of oil is flowing in to
cylinder. Piston retracts slowly.
B ,rr tr"qrEl 32? Oil Hydrauiic Circuils

3.11.4 Types o, Load on Hydraulic Cyllnder :

OpposinE load (positlve load):

If load is acting in opposite direction to the motion of
cylinder, then the load is said to be opposing load.
Over-runnlng load (nsgatlvo or runnlng-away load)i
If load is acting in the same direction ol motion of cylinder,
then the Iosd is said to be over-ruaning load.
Examples o, opposlng load:
1. Weight ofload during lifiirg.
2. Cutting force during metal cutting.
3. Packing friction in cylinder
4. Friction between load atrd contact surface
Examples ol over-runnlng load:
1. Weight ofload during lowering.
2. Weight ofpunch assembly during purching dowowards.
3. Weight ofdriU assembly during drilling downwards

3,11.5 Applications ol Meter-in, Meter-oul and

Bleed-off Circuits

Oppositr, loads Runnitrg -ai.ay loads

Meter-in circuit \,ES NO

Bleed off circuit YES NO

Meter-out circuit \TS YES

Meter-in cicuit and bleed ofr circuits are preferred for

opposing loads only. They are not preferred for over_runnitrg
loads. Over-running load will caus€ cylinder lung or jerkv
motion of cylinder.
Meter-out circuit csn be uEed for both opposing load as well
as oYer running load.
ffi,." lrserel 3-23 Oil HydraLrlic Circuiis

3.11.6 Advantag€ and Llmltatlons ot Meter-out, Melerln

and Bloed.oft Clrcults :
Meter.out circuit
Advantages ! . R.tum line has flow conhol valve. Hence, it
can resist over-rrrniiag load. Hence, it catr be
used for both opposing loads end over-
rundng loeds.
r Pressure diop in FCV will not affect force
develop€d.
Diaadvantages:. Prcssur€ int€nsificstion occurs st rod
end if ECV is closed (incase of meter-out for
extension).
. Closing the FCV iDcrea-ses the back
pr€ssure, due to this, net force d€veloped will
Educe,
Meter-in circuit
Advantages : No pioblem of pressure inteD.sification.
Closiog the FCV does not afrect the force
developed.
Disadva-ntages :. B€turn line is a liee path back to the
reservoir. Hence, it can not resist over,
running load. It can be used for opposing
loade only.
Cyliaden may lung during stroke. Cylirder
movement may be jerky.
Pressure drop in FCV may reduce force
develop€d.
Bleed-off circuit
Advantages : Saves energy, avoids over-heating of oil.
Pressure drop in FCV will not affect force
developed.
No problem of pressure intensification.
Closing the FCV do€s not affect the force
developed.
Disadvantsges Return line is a fiee path back to the
reservoir. Hetrce, it can not resist over-
runing load. Hence, it can b€ used for
opposi[8 loads oDIy.
ffi ,rr (r""r.) 3-24 Oal Hydraulic Cncuits

Ex.3.11.1 ln lhe meler-oul hydraulic circuil shown an ligur6, the diamoter

ol pislon and pislon rod ol ths double acling cylind€r are 10
cm and 6 cm respeslvely. Tho pressure reliel valve is sel lor
3Oo bar. Calculate lhe pressures at cap snd and head end oJ
the cylind€r il lhe llow control valvs is closed completoly
during onension o, ths cylinder.
Soln. :
Dats : I
D=10cm,
d=6cm,
PR = 300 bar
a

Fis, P.3.ll.r
ln the met€r-out circuit showB in figur€, iI FCV is closed
during extension, thetr, oil can not flow to cylinde!, henc€ pressure
increases to pressure reliefvalve setting 300 bar.
Pressuie at cap end of cylinder (Pr) becoDes 30o bar.
But, there will be itrt€nsfication of pressur:e at md etrd.
Pressure at rod end becomes more than the Pr€ssurc rclief
valve setting.

= ,,,o-u! = P,"#u, =soo'#% = 468.?5 bar

",
Pressure at rcd end of cyliDder (Pr) becomes 468.75 bar'
Notice here that, pressule at rcd etrd is tllore than pressule
rclief valve setting.
ffi,t, tr"tt.t 3-25 Oil Hydlaulic Circuils

3.12 Sequencing circuits using sequence valves:

3.12.'l Circuil lo Operale Two SAC in Sequence :

E E

1 # #
1

Fi& J.r2.l

Fig. 3.12.1 shows the hydraulic circuit usiDg one sequence

valve to conhol two operations performed in a pmper
sequence in one direction only. In the other directioD, the
op€ratioD i-s simultaneous.
Therc ar€ two sidgle acting cylinders which extend one aftcr
the other. While retracting, they move tog€thei.
Wlten we keep the lever of &2 DCV in first position, oil
under prtessure is supplied to inlet port of sequence valve. It
flows directly to outlet port'l. Hence cylinder-1 extends 6r€t.
By the end of exteDsion of cylinder-l, pressure in the liDe
increases and he[ce the poppet of s€queme valve is lifted ofl
iiom its seat t allow oil under pr€ssurc to flow to port-2,
helce cylinder-2 extends.
When the lever of 3/2 DCV is shiff€d to second poEition, both
cyliaders !€tract siDultsneously.
lgBl rep (MsarEr -?q -
3.12.2 Circuil lo Operate Two DAC in sequence in One
Direction Only :
w-m14
O- Explain with neal skstch the working of sequencing circuil for
the two dolble acting air cylinders.

Example: Stamplng circult

. FiB. 3.12.2 shows the hydraulic circuit using one sequence
valve to control two operations performed in a proper
sequeDce in one direction only. In the other dircctiou, the
operahon is simult€neous.
. In the example an application for stamphg the work piece is
consideEd. It may b€ for embossil8 on metal coins.
2

Fi9.3.12.2
ffi
. During extension, the movablejavr ofthe Yice holds the work
piece frrst, and thea the purch moves downwards.
. During retraction, both will move together.
. Ihere are two double acting cylinders which extedd one a.li€r
the other. \,Vhile retracthg, they move together.
. When we keep the lever of tU2 DCV in first position, oil
under pressure is supplied t-o inlet port of sequence valve. lt
flows directly to outlet port-1. Hence cylinder-1 extends fiIst.
EEI ,r, (usur.) 3-27 Oil Hydraulic Circuits

. By the end of extension of cylinder-1, pressure in the line

incrcases and hence the popp€t of sequence valve is lift€d otr
from its seat to allow oil to florv to port-2, cylinder,2 ext€nds.
. When the lever of4l2 DCV is shifted to second positioD, both
cylinders rehact simultaneously
3.12.3 Circult to Operate Two DAC ln Soquencs in Both
Directlons :
92013
O. State any lwo applicalions ol sequencing circuit.

Examplo No. l: Furnaqr door

. The Fig. 3.12.3 shows the hydraulic circuit using two
sequence valves to control two operations performed in a
proper sequenc€ in both dircctioN. The circuit uses
manually operated 4/2 DCV.
. In the example an applicatiotr for keeping the work piece
inside the furnace is coBsidered.
o The furnace door t b€ opened first, and then the work piece
is pushed in to the fumace.
r ltVhile retracting, the pusher rod is t€ken back first and theD
the door is closed. 2

c2

3
F
3

Dn bil
T
3
T-LI
t----r-i

EZTTN
Fig.3.12.3 EIZ\\I
ffi,r" (rsat.) 3-?A OilHydraulic Circuils

. Tte above FiS. 3.12.3 shows the hy&aulic circuit using two
to conhol two oPeratiotrs performed in a
sequence valves
proper sequence in both dhections. The circuit use8
manuatly operated 4/2 DCV.
. III the example showD in the above Fig. 3.12.3, filst the door
of the fumsce should open, and then the pushor should push
the work piece inside the fumace. Aft€I this, the pu-sher
should come back and door should close.
. ln finst position of.y2 DCV, oil flows to cylinder C1, hence C1
retract, the door opens. By the comPletion of r€haction of Cl,
pressure in the line increases hence the sequetrce valve Vl
op€ns to allow oil to flovi, to cylinder C2. Hence C2 exten& to
push the work piece into the fumace.
. In second position of 4./2 DCV, oil oows to cylinder C2, hence
C2 retract, the pusher comes back. By the completion of
rctmction of C2, pressure in the lin€ incrcases hence the
sequence valve V2 opens to allow oil to flow to cylinder Cl.
Hence Cl exterds to close the door ofthe fumace.

Erample No.2 : Drllllng machlna

. The above Fig. 3.12.4 shows the hydraulic chcuit for drilling
a work piece.
. In this example, firct the work piece is held 6rmly itr ttre
vice, and then &illing is done. Afttr this, the dril bit is
rcmoved 6rst and then the work piece is released.
. The c cuit uses two sequence valves to control two
operatio.s performed iD a proper sequence in both
aliiections.
. The circuit uses manua]ly oPeret€d d2 DCV.
. In firrt position of4l2 DCV, oil flows to cylinder C1, hence C1
extetrds, the movable jaw of the vic€ holds the work piec€. Bv
the completion of extension of C1, pressure in the line
increases hence the sequence valve Vl oPens to allow oil to
flow to cylirder C2. Hence C2 extendB to move the drill bit
dowuwards.
ffi ,rr (r""r.) 3-29 Oil Hydraulic Circuils

In second position of ,U2 DCV, oil flows to cyliDder C2, hence

C2 retract, the drill bit is removed fiom the work piece. By
the completion of rctraction of C2, pressure in the line
increases hence the sequence valve V2 opens to allow oil to
flow to cylinder C1. Henc€ C1 retracts to move the movable
jaw backwards to release the work piece.

c2

l-33
3
B

oa nir
T
2 3

EZIIN
EIZNT
Fig.3.12,4

3.13 Sequencing Circuits using Limit Valves :

Herc the sequencing is achieved due to the poaition of

pistotr.
Dudng exteDsiot! or r€traction of first cylinder, it operates
the liDit valves wheo the piston reaches a particuLar
position, so tiat, oil flows to the secoDd cylinder, and the
second cyliDde! starts performing its stloke.
I'his nethod of sequenci-ng is called "1roaition ooDholled
sequeDcing".
A limit valve tu a "cam operated spring return type 3/2
directiotr contiol valve".
ff] tre lusatel 3-30 oil Hydrauhc crrcuiis

Example: to operate a DAC and a SAC ln sequence :

c
II
T
B
LV1 it
I

l'is.3.13.1

. In first position of lever of {/2 DCv, the DAC ext€nds. By the

eod of exteNion of DAC, the cam presses the limit valve,
hence oil flows to SAC, and SAC extends.
. when the leve, of 1,/2 DCv is shifted t second position, DAC
retmcts, and simultaneously, the SAC will also retract.
Example: to oparate two DAC ln sequence:

c
[-F 1

T
tv2 LV1
#

Fis. -l.l-1.2
ffi ,r, tr"ut.l Oil Hydraulic Circuils

In first position oflever of.r2 DCV, the DAC extends. By t}le

end ofextension offirst DAC, the caIll pless limit valve Lv1,
hence oil under prcssure flows to cap end ofsecond DAC, and
secoDd DAC extends.

When the lever of4l2 DCV is shifted to second position, DAC

retracts. By th€ end of retraction of first DAC, the cam press
limit valve LV2, hencc oil under pressure flows to rod end of
second DAC, and second DAC retracts.

3.14 Sequencing Circuits using Limit Switches:

. Here the sequencing is achieved due to the position ofptuton.
During extensiotr or retraction of a cylinder, it operates the
limit s*itrch when the piston reaches a particular position.
. When the liDit switch is pr€ssed, the
electric current flows t,
soleaoid of the "solenoid opeiated DCV, due to which, the
spool chaoges its position. Oil flows t the second cylinder,
and the second cylinder stsrt.s performhg its skoke.
. This is another metlod of"position-controlled sequencing".
. Limit switch is an electrical sv/itch which wheD pressed by
any moving eleme[t, it makes the electricrl comectiotr to the
solenoid of'soleaoid operated direction control valve".

Exampl€: lo opor6te a OAC and I SAC ln lsquenca:

In first position of lever of 4/2 DCV, DAC extends. 8y the end

of extplsiotr of DAC, the csm press Iimit switch [S1, current
flows to solenoid Sl, spool of 3/2 DCV shift,s to second
position, hefte oil flowe to SAC, end SAC exten&.
When the lever of4J2 DCV is shift€d to second pGition, DAC
rctrscts. The cam relea8es the limit swikh, spool of 3/2 DCV
6hifts back t its original position, hence oil flows ftom SAC
to tank, ald SAC retracts.
El,r, (r""r=) 332 Oi! Hydraulic Circuits

C R
n
tsl

T
S1
T

Fig.3.14.1

Eramplo: to opgrato two DAC ln 3oquonca :

. In first position oflever of,U2 DCv, tlle DAC extends. By tlle
end of extension of frrut DAC, the cam press limit switrh,
hence oil under preasure flows to port-1 of second DAC, and
second DAC extenala.
. When the lever of 4/2 DCV is shift€d to second position, DAC
retract€. By tlle eDd of rctraction of 6rst DAC, the cam pless
Iimit switah, hence oil under pressure flows ta port-2 ot
second DAC, and second DAC r€tlacts.

c
II fi
LS1

B
2
#
T
S1 S2

Fis.3.14.2
EEI (use-e) 3-33 OilHydraulic Circuils
'r"
3.15 Synchronizing Circuit:
w-2014
O. Explain with neat sketch the working ot motion
synchronization circuit with the help ol flow divider, lo conirol
lhe movement ol two double acting cylinders- Synchronization
m€ans making lwo or more number ol cylindors to move
simultaneously, together.
Itr fig. 3.15.1, two cylinders arc connected in pamllel t-o a 4/2
DCV. It looks like a synchronous circuit, but it is not so. The
two cylinders move together only if the opposing loads on
them are equal. lf opposing forces are unequal, then the
cylinder.flith less opposhg force will extend fiIst.

ris.3.ls.l
h fig. 3.15.2 the two cylinders are hooked in sene6' the
outlet of one is connected to inlet of other. Now, even if the
opposing forces orl them are unequal, they move (extcnd)
together

ris.3.15.2
The sp€ed of extension of the cylinders depends upon
cylinder diameter and piston diameter. Cylinders should be
chosen by performing pmper calculations.
Wt" MSBTE) 334 Oil Hydraulic Circuils

3.16 jy9Ey!! g!..per circuit:

w-m11
O. Explain rvith naat sketch, wo.king of hydrautb shaper.

s-20r4
O. With the help o, neal circuit diagram, exptain the tunctionang oi
hydraulic
Shaping is a machining process, in which, a cutting tool
reciprocatiag on the stetiona-ry work-pipce.
The cutting tool cuts t}le metal by shearing action.
The cutting tool is fitt d in the tool-post, tool-post to clapper
box, clapper box to cmss slide, ard cross slide to ram.
R€ciprocation ofran causes the tool to cut the metal.

fi
LSl
-
L52

sl s2
T

l'ig,3.16.1
Ef (,us"r.) Oi Hydraullc Cncuits
't,
The hydraulic shapirg machine i6 shovtn in Fig. 3.16.1. Its
ram is mouDt€d on a double rod end DAC.
The cutting stroke ofthe ram ehould b€ slow aod the retum
Etroke should be fast. For thiB, we can chooEe meter out
circuit.
Continuous reciprocation of ram can be obtained either by
using double solenoid DCV or by using double pilot DCV. we
need lihit swit hes if soleooid DCV i6 chosea atrd limit
vatves if pilot-operat€d DCV ie chosen.
In the above example, double solenoid DCV and lihit
switches aie used.

4J2 double-aolenoid DCV is used with two limit switches on

either eDd of the pistotr rod. The pistoD rod, while
r€ciprocating, actuates these limit switahe6, wbich intem
actuates 4/2 DCV. Thus automatic ieciprocatioa of ran is
achieved.

In first position of 4/2 DCV, oil flows from P to A aod B to T.

T'hi.s flow is through check valve. Hence the piaton moves
fa8t.

In secodd position ,U2 DCV, oil flo*'s ftom P to B aad A to T.

This flow is thmugh flow control valve. It is a conhotled flow.
He ce the piston Doves with coatrolled speed.
The stroke length and position of stroke can b€ easily
adjusted by adusting ttrle position of limit svtitches Speed of
cuttiog strcke car be adustsd by adju6tiry the FCV opening.
EEl,r" (rs"r.) Oil Hydraulic CircLrils

3.17 Hydraulic Milling Machine or Hydraulic Surface

Grinding Machine :

s2012
O. Draw thg hydraulic circuit fo. milling machine.
s-2013
O. Draw a hydraulic circuit diagram ror milling machine to control
its table movem6nt_
w-2012, W.2013
O. Explain with neat sk€tch hydrautic circuit lor mifling machin€.
w_fr14
O. Explain wilh neat sketch the working ot hydrautic circuit used
tor milling machine.

lj

LV1 LV2

Fig.3.l7.l
IFP (MS 3-37 o raulic Crrcuits

ln milling machine or sutface griDder machine, the work_

piece is clamped on the machine table. The machine table is
made to reciprccate using a double rod end typ€ DAC Tllat
iBthe work-piece is made to reciprccate against a mtatirg
multi-point cutting tool (miUing cutta or grindhg wheel)'
Thus the cutting tool cuts the 6etal.

Continuous reciprocation of rse can be obtained either by

using solenoid DCV or by using Pilot-operated DCV We need
liEit switches if solenoid DCV is chosen 3nd liEit valve6 if
pilot-operat€d DCv is chosen.

In this example, pilot operated DCv and limit valves are

used.

DCV is used with two limit valves oD either

4,/2 rtouble-pilot

end of the piston rod. the piEtod rod, while reciprocatitrS,

acluates these [mit valves, which intem a€tuates 'U2 DCV
Thus automatic rc.iProcatioE of ram is achieved'

In first position of ,U2 DCv, oil flows from P to A alrd B to T'

Hence the piston extends.

In s€cond position 4/2 DCv, oit flows from P to B and A to T'

Hence the pbton retracts.

Flow contml valve is placed in retum line to the reservoir,

hence it is mete, out circuit with same spe€d in both strokes'
@f ,r" 1r""r.1 3,38 Oil Hydraulic Circuits

3.18 nerative Circuit:

92{113
O, What is rogenerative hydraulic circuit ? State any two
applicalions of it.
w-n13
O. Explain regenerative hydrautic circuit.
. By ?egenerative circuit, we can increase the speed of the
cylinder at the cost of reduction in force develop€d.
. Speed will be inoeased from qyA to Q/a, but the force
developed will reduce from p x A to p x a.
. Oil comiDg out from rod erd port "R" is made t join with tlle
pump delivery and to flow to cap end port "C".
(A) Regonoratlvo clrcuit by uslng 3/2 DCV :

T
u,
T
I
D

OD 1
c

Fig.3.18.1
tfl IFP (MSATE) 3-39 Oil llydraulic Circuils

g/2 DCV A
Fig. 3.18.1 shows Reg€nerative circuit by using
3/2 DCV is used to opetate double acting cylinder.

Ia first position ol3/2 DCV.

. llris is regeneratrve exten-sion stroke
P is co.nected to both C and R. T is closed.
Netforce = F = Fr -f', = Ip x Al - [px (A- a)] =Pxa

Due to this net force. DAC exteods.

o+o O _ __g_
Velocity ofpistoo = t=-A-=;
Ia second positiotr of g,/:l vdve.
. This is normal retractioo stroke
OiI flows from pump tD R and C to T. P is closed
During this stroke, Foree F = p x (A - a)

Due to thb folce, DAC retracta.

o
velocrty or prston = v= tA_a)
(B) Rsgeneratlve circult by using rsgeneratlve tyPe mld'
posltion /U3 DCV:

Fig. 3.18.2 shows Begenemtive circuit by using regpnerative

cenhe hid position {/3 DCV.
tD first positioD of slrool of 4:l vdve.
It i-s trormal exteNion 6tmke.
OiI Ilows hom P to A and B to T.
During this stmke, Foft:e F=PxA
Due to this forte, DAC extends.
o
VelocitY of Piston = v=i
 3-40 oit Crrcuits

c
I Qo

Fig.3.18.2

In niddle positioD ol4ll DCV.

. This is regenerative extension stmke.
P is connected to both C and R. T is closed.

Net force = F=Fr-F: = IpxAl-lpx(A_a)l =pxa

Due to this net force, DAC extends.

velocity ofpiston = "=*=3=tr;

In eecond position of st ool ol,g:| velve.
This is normal retraction shoke.
Oil flows fiom P to B and A to T
During this stmke, ForteF=px(A-a)
Due to this force, DAC rekacts.

Velocity olpistotr = v=(A-a)--q-

@t" MSBIE) 3-41 oir lic Circuils

(C) Regenerative clrcult by pllot to close check valve :

-rr
o

a B

T T

(r) (b)

Fl& 3.183

In 6rst position of 42 DCV, oil flows liorn P to,q-

This is regenerative extension stroke'
There is no pilot Pressute, aod hence, the "pilot t' close
check valve" remain oPen.
Net force = F = F, -F, = IpxAl - [px(A-a)] = p x a
Due to tlfs net force, DAC exteads. Oit coming out ftom rod
etrd port joins with the pump dischargB and flows to caP end
port'
O+o a = --e--
Velocity of pistoD
ln second position of 'U2 DCV, oil llows Eom P to B and A to T'
nfs
is normal rctractrotr skoke.
Due to the Pilot PreEsur€, the 'pilot to close check valve"
closes. Oil flows to rod end of the cylinder atrd the cylinder retrac'ts'
Force F = px(A-a)
o
Velocity of Piston = t=A-
@ IFP (MSBTE) 3-42 OilHydlaulic Circuirs

Ex.3.18.1 : lnside diamelor ot a doubtg acting cytincter js 10 cfi and

dlamoler, ol pBton rod is 5 cm. pump dischsrgo is
l20O cmrs, Forc€ raqured during er(snsion is 1 lon,
Find the 'pressuro of oit" and "sp€ed ot piston" during
exlension, with normatcircuil as we as reoen€ralivo circuii.
Also, compars the "pump dischsrg€" and "rale ol flow ol oil
coming oul ol rod end port durino sxlsnsion,.
Soln. :
Give! dsts
D=10cm A=78.5cm,
d=5cm a=19.62cm,
Q = 1200 crD3A
F = 1000 ksf
Ccae I I Consider norDal cirruit :

Pressure of oil during ext€nsion

F 1000
P =A = 78j = l2.71wcDz
Sp€ed of extension ofcylinder
6 1200
' = i = 785 = l5'2a cnr's
Case 2. : Consider regetreretive circuit :
Prcssur€ ofoil duritrg extension

p =;F = i6;t
1000
= 6o.e65 L8/cE'
Speed of exteD-sion of cylirder
o 1200
" =; = 19c' = 6l'14 cny's
* Both arc increased by 4 times.
Rat€ of flow of oil going in at cap end = Q + q = v. A
.. Rate offlo\r ofoil comhg out at rod end = q=(v.A)-e
q
= (61.14 X 78.5) - 12OO = 38(n cm'/s
Notice herc that, the rate offlow ofoil coming out ofrod end
port during extetrsion is not smatl. It iB B times Dore tha[ the
pump discharge. Thst is why, the speed ofcytinde! is increased by
4 times.
ffi,r" MSBTE) 3-43 Oil Hydraulic Circuits

3.19 Hydraulic Circuit lor Fast ApProach, Slow

Cutting and Fast Return ol Machine Table :

w"2012
o. Draw and explain hydraul ic circuit diagram ol a sysl€m having
DAC has Slow and telurn
A deceleration valve is used in th€ circuit to slow down the
speed of DAC during extension a"s shown in the
Fis.3.19.1.
Dieleration valve is a combination of a 2i/2 DCV' a llow
control valve antl a check va.lve. Itr forwad flow, it allows oil
to flow tltmugh its ,y2 valve. But when the rcller is pressed,
2/2 valve closes and allows oil to flow throwh f'CV Dud4
reverse flow, it allovts oil to flow through check valve'

I #
?

Fig.3.r9.l
 @l',." sBrE) 3-44 oit Ctcuils

. Machine t€ble has a double rod erld DAC. Work piece is

mounted on the machine table. The cutter rotates on its
position. Machi[e table reciprocates.
Faat approach :

In fiIst position of DCV, oil flows from p to A and B to T

4./2
oil flows through 2/2 valve to the DAC, aod the DAC starts forward
Btroke with high spe€d.

Slow cuning :
During forward shoke, the machine table presses the roller
of the deceleration valve, due to *hich, 2/2 valve closes. Now,
oil
has to flow through the FCV. The flow I5te is reduced, and hence,
the sp€ed of turther forward stroke is reduced.
Faat relurn :
When the spool ol.V2 DCV iE shifted to the second position,
oil flows from P to B aDd A to T. this flow is a free flow thrcugh
the
check valve. DAC returDs wilh high speed.

3.20 Dual Pu mp Hydraulic Circuit :

9nt11
O. Explain the circuit for high-low doubte pump systsm for punch
press application.

. A combination oltwo punrps, big pump a_ud small pump, is

used itr press circuits i_n order to save power and avoid over
heating of oil.
. Big pump can punlp lsrge quantity of oil at small pressure.
Its discharge comes to zero at high preseure.
. Small pump gives smsl quatrtity oloil but at large pressure
. Big pump can pump larSe qua[tity of oil at sma]l prcssure.
Its discharge comes to zero at high pressure.
. Small pump Sives small quatrtity ofoil but at large pressure
 3-45 oit Circuits
l4E rFP MSBTE)

Aclual Dunchinr operation is only for a small Portion of

t,o the thickness ofwork piecel High
"*t"""ion "t.ol.it"q"a
pressure oil is required only during thst much of shoke time'

Bg

Fis.3.m.l
. Oil flows t,o tbe cylinder from the big puEP during the entir€
extension ald rettaction strokes ODly during the small
lensth of actual punching operation, this big puDp becomes
,rna-Ut" to p'rmp oit During this time. oil Fom the
small
pump flows to tire cylinder to Perforrn punching operatiotr'
. bi* pr*p is at work when large quantity of oil is required
.rr_a p...p i" ,t t"ork when large pressure is required'
. "-"il
Durinc idie period, as Pressure is higb. dischsrge of big
or-r'i" ,."o. Onty Ge small discharge of small Pump flows
irackto t"be resewoir tbrough Lhe pressure reliefvalve
Poy/er consumption during idle period = pressure x rate of
flow of oil
. As the rate offlow is le$, power coDsumption i3 also less'
@t" E) 3-46 oit raulic Circuits

3.21 Hydraulic press Circuit usi ng Unl oading Valve :

oAc

IXE
T

Fig.3.2l.l
Itr firct position of spool of ,V2 DCV, oil flows from p to A and
B to T. Hence, the cylinder extends, srld the punch moves

ID secoDd position of spool of 4/2 DCV, oil flows liomp to B

and A to T. Hence, the cylinder retracts, and the punch

During downward stroke, ffi punching the sheet metal,

the force required is very large, and hence, the pressure
reliefvalve is set for high pressure.
But while return stroke, the force required is very small.
rwhich is oDly ro move back the punch assembly), aDd
hence, the udoading valve is set for less pressure.
Cylitrder is kept iD retracted position dunna idle period
of the machine (dudng loading and unloading of work
piece), so that, oil flows back to reservoir at very less
pressure, thereby, it avoids over heating of oil atrd saves
W MS 347 oil Circuits

is s€t lor a
Ex.3.21.1 Consider a hydraulic prsss in which, the rcliel valv'
pressure ol 5OO bar whictl is roquirsd tor punching lhe sh66l
melal, Th€ pump dischargo is O.O4 mrs. Celculals lhe power
consumption, ll unloading valve is us6d in the syslem and is
sel ior 5 bar, thsn calculaiolhe power consumpiion' Calculalo
the power saving end porcentags of power sgved'

Soln. :
Dsta : PR = 5OO ber = 5oo x 1S N/E'z

P,,=5bar=5x1dNlm'
Q = 0.004 mVa

Power consuDptioD during idle period is given by'

= Preatture x dischargp
Posor
a) Powe! coD.sumption during idle period without ualoading
va.Ive

= 5OO x ld x 0.(xN = 200000 Wqtt

b) Power c.oEsuDptioa dudng idle period with unloading valve

= 5x 10x0.004 = 2000 watt'

c) Power ssved dudrg idle P€riod

= 200000 - 2000 = 198000 watt.

d) Pettentagp power saved during idle period
savinE in @wer
xl00%
origiDal power

= ffi,roo=ts*
EEr,., MSBTE) 3-48 oir lic Circuits

3.22 Hydraulic Circuit usi ng Counter Balance Valve :

B
Counler

L
16li6t

FiB.3.22-t

In first positioD of spool of 4/2 DCV, oil flows from p to B and

A to T. Oil flows through the check valve, and this is a free
flow. Cylinder extends and lifts the load.
When the lever of 42 DCY is shifted to second position,
connection is made llom P to A and B to T.
Once the pressue below the piston reaches the preset
pressuie, the counter balance valve opens and allows oil to
flow through it. The cylinder rctracts and hence load
descends-
As counter balance pressure is oaintaioed at the bottom of
the piston, the load is balanced from both sides. The load
descetrds slowly, it uTon't over-run.
If there is no count€r balatrce valve, thetr the load will fall
rapidly. This causes damage to the cylinder end cover, the
seal may rapture and oi1 may stsr"t lefing fiom it.
For all degative loads, count€r balance valve is necessar.v.
Counter balance valve is usually set for t.J times the lo;d
induced pressure (LIP = over runnirg loa(V aiea of pistotr).
 oir Cncuils
W1 tFP BT 3-49

3.23 Deceleration Ci rcuit or Cushioning Circuit :

Tte above circuit shows cushioning of a DAC using cam
operated flow contlol valves.
V1 and V2 are the t\,ro cam opemted FCV A canl operated
flow contml valve allows free flow when it is not actuated
and controUed flow whea it i5 actuated'
In first position ol 42 DCY, oil entert through the check
valve ofVl to head end of DAC. Hence piston extends'
During extensiotr, once the cam reaches the valve V2, cam
actuates V2 causing the flow through V2 to get controlled'
Hence fuither foNard xootion will be slov{. So cushioning is
achieved at the end of exteEsion stroke.

lig. 3.23.1

h second position of 4y2 DCV, oil enters through the check

valve ofv2 to rod end of DAC Hence pfuton retracts'
Duimg retraction, once the cam reaches the valve V1' cam
actuates Vl causing the flow through Vl to get contmlled'
Hence further backward motion will be slow. So eushioning
is achieved at the end ofretraction stroke
l{l trp i,I 3-50 oil

3.24 Application of Shut e Valve :

Fig. 3.24.1 shows the applicatior ofshutfle valve.

It has two "push button operated spring retum type
trorma]]y closed 3/2 direction contml valves", a single actitrg
cylinder, and a shuttle valve.
In normal position, tlre single acting cylitrder is iD retracted
position.

By pressing the push buttoq of any of the two valves, or by

pre$itrg both together, the singte acting clitrder ext€trds.

I vtH

A
312 Dcv

Fig. -1.24.I
lql rFP ( MSBTE) 3'51 Oil Hydrau lic Crrc!its

3.25 Application ot Twin Pressure Valve :

Fig. 3.25.1 shov{s the aPplication oftwio plessute valv€.

Ihe circuit has two "push button operated spring retum t]'pe
normatly closed 3i/2 direction contml valves", a shgle acting
cylinder and a hl,.in Pressure valve.
In trornlal position, t}l€ single acting cylfuder is in rctracted
position.
If and only if, the push buttons of both valves are pressed
together, then only the cylinder wiII ext€nd.
Such circuits are safety circuits catled "two hard operation
circuits' which safe8uard tie hands of the oPemtor in case of
hy&aulic press o. Pneumatic Press.
Both haDds of the operator are made to engage in Pressing
the buttons, and theteby the chance of his hand coming in
between the punch and die is avoided.

Singl€

3D DCV
#

fis.1.25.r
 IFP (MSBTE 3-52 oi H Ctcuils

3.26 Application of "Pi lot-to-Open Check Valve":

In hydraulic syBtems, even with closed center mid-poBitioD of
dircction control valve, an over running load will Dot stop
positively; it starts creeping downwards slowly due to intemal
leakage in diection contml valves.

IL
h-
i T 1'

Fis.3.26.1

All spool tlTe direction contlol valves allow a small amount

of internal leakage of oil, and it is unavoidable.
The Pilot to open check velves are used to avoid
cr€eping doqrn of the load when the direction conhol
valve is kept in center positioo so as to stop the load.
Figlre 3.26.1 shows hydmulic circuit for an application of
'pilot to open check valve,.
 MSBT 3-53 oil Circuiis

. The "pilot to oPen checL valve" is fitted to the bottom end

po"t oftrc rvma"" itB pilot connection is taketr from the
top end Port.
",.a
. In Gdt Dosition of 4/3 DCV, oil ftows liom P to B aDd A to T'
t'li. flo* i" forward flow from its inlet to outlet of check
vafve, anrl this flow is allowed. Hence the cytinder extend6
and the load is lifted.
. ID seconil Positiotr of 4/3 DCV, oil flows from P to A and B to
T. This ftow is reverse flow for the check valve, it is not
pilot
alloweil, but, the check valve opens b€cause of the
pressure. Hence the cyliDder retracts and tie load is lowered
. ihe mid-position of 43 DCV is used t,o stoP the load in
. Notice that trcth the Ports A and B are open to tsDk Port T in
the ceotd position This t]?e is caled f,ush tl/I'e center
Dositioni it allows pilot pressure to droP to zero'
. i. there is Do pilot pr€ssur€. the pilot'to-open check valve
does oot ooen. ii remain closed lt will not allow even a droP
iio to nou, rfrro"eh it. And thus the cytioder is locked The
-downwards.
load will not creeP

Opp6ing load (Posltlve load) :

when "dircction of actron ol load" and "dir€ction of
dotion of load' are opposite to each other, then it is called
opposing load.
over.running load (runniag_awsy load or negative load):
when "firectiotr of action ofload'and "direction of motion of
loaal" are saEe, then it is called over_running load
GeDerally,
. o"riog Ufting, *eight is acti4 in dowtrvtard ilirection and
the lo;d is m;ving in upward dircctiotr so, this is oPPosing
load.
. During lowering, weight is acting in downw€rd dit€ction
and the load is also moving downwards l'his is over'
running load.
. When kept idle or stationsr:l, the "down*ard actiDg load'
is cotrsidered to te over'rulning becaus€, the losd tcDds to
creep (move slowly) do*nwsrd6 due to int€msl leakage ir
the direction coDtrol valve.
 MSBTE) 3-54 oit Circuils

3.27 Hydraulic Time Delay Valve Circuit :

w-20r4,
o. What is time delay cjrcuit ? Explain any one lime circ!it.

T
#

Fic. -1.27.1

When tie push butto[ of BD valve "A" is press€d, oil u.Bder

pressurc flows to iolet of time delay valve.
It flows thlough the check valve aDd quicL.ly frIs i-n ttre
reserToir- It exerts pressure on the spool of pilot operat€d g/2
valve, hence the spool u,ill sbift to make the coDnection iom iDlet
"P' to cylinder port "A and hence the silgle actiog cytinder
extends.
Wb€tr the pulh butt D of A12 valve is Eleased, the spool of
pilot operated 2 valve srill not shift bact u_ntil the prcssur€ in
reservofu falls below the spring force. Oil flows is slo*ly thmugh
the flow contDl valve back to r€servoir saod heoc€ p."""or"-i"
<iropping slowly.
Once the piessure becomes lese than the spriog pressure, the
Bpoolwill shift bacl automatically to close the inlet, and makea
connectioa froE cylinder port .A, to outlet port -I-, bedce the
cylinder rehacts.
The tirDe
- control valve.of delay can b€ easity a4iust€d by adju.stiDa the
Ilow
ffi,t" t"su-.r oil licCarcui:

3,28 'qolvej qayirlg" in Hydraulic Systems:

Consumption ofpower by the machine duriog idle period is
the loBs ofpo*er.

Idle pe.iod is the ti6e spetrt during lo3di-ug and unloading of

tne machine.

Idle period is unavoidable, but can be Einimized

coBiderably by automation.

Hug€ loss of power is observed in any hydraulic machine

durins idle period-
Because oil flows continuously back to the reservot through
the relief valve at very high pressure without doing a,ty
work during tbe idle p€riod.
"Contitruoua floll, of large quantity of high pressurc oil
during idle period tbmugh pressure reliefvalve causes hug€
loss of trnwer alld overheating of oil".

Causo3 ot powor lcis :

. Idle period (Equired for loading and uDloading).
. HiSh discharAc (necessary for obtaitring requircd epeed of
op€ratiotr).
. HEh pre-asure (trecessary for pmducing requiied amount of
force).
But neither speed nor for.e fu r€quired during idle period. The
c?lbder remains ststionary during idle period.

Force a.trd Bpeed arc required ooly duridg actual worki.ng of

the machine, s.trd this working pcriod is very less compar€d to tie
idle period in any hy&aulic machine.
ffi ,r, tua"t.t 3,56 OilHydraulic Circuits

Power consuoption (Watt) = pre$ure

/N )' ** rn"- (c)
\! /
l-m. /
. So,it is possible to reduce power consumption du.ing ide
period by keeping mirdoum pressure aod minimuh
dischargp.

A) Poier saving by rcducing th€ pr€$ure durlDg idle period :

. By using ulloading valve,
. By using tandem-centr€ 6id Position valve.

B) Pow€r ssylng by rcducing the dischlrgc during klle pcriod :

. By usiag accumulstor,
. By using dual puDp.
These four cirtuits are already discussed earhet ilr the
previous topics.
 M 3-57 oil Circuits

3.29 lmportant Examinalion Ouestions and

Answers
Please refer ebooh fot complete solution
Note :

1 Pteose downlad our free e'booh for dztaiJed arcwers

ol fo\ouine qu.stiarc.
2 Nl Questions & Answers cooer thz comPlete chapter'

u.rtg gJ! LCV

S.1 Opcntba SAC

Q.1 Stst€ the use of DCV showing it's position in the

(913)
circuit.
3.11 glro6d Control Cttcotti
Q. 1 ltow the speed oi hydraulic motor is controUed ?
Explain it with treat circuit diagram (W-13)

Q. 2 Explain with nest sketch the working ard application

of met€, in circuit ls"ction311 11
(S-11' S-12)

OR

Q.2 Whst is the punPose of meter in circuit ? Draw the

metcr in hydraulic circuit for regulating the sPeed of
piston in cylinder. lS"ctian 3.11 11
(W'12)

OB

Q.2 Draw a cfu:uit diagran of speed control when Piston

move forward in a Eciprocatiag hy&aulic cylinder'
tsection 3.11.11 (9r3)
OR

Q. 2 Sketrh atrd €xplain hyrlmulic circuit for meter in'

(w-13)
[Section 3.11.1]
m' IFP (MSBTE) 3-5a Oil Hydraulic Ctcuils

OR
Q.2 Sketch and explain meter in hydraulic circuit to
contml the speed of extension of DAC. Explain why
meter in circuit is not prefeEed for over running
loadr. [Section 3.11.1] (914)
Q.3 Draw and explain meter out cin uit. 15€ ction J.1t.2l
Q. a Draw bleed-otr hydrautic circuit and tabel it.
tsection s.11.31 (S-r2, W-12, W-tg)
Q.5 Compare metcr-in circuit with meter-out circuit with
respect to well labelled diagrao, working, festues,
advantages, limiAtioDs arrd applicatiolls.
ISection 3.11.21 (W-r,r)
3.r2 Sequ€nchg Ctriutt. usb* Soqucncc Ve,lv6.
Q. 1 State any two applicatioDs of sequencing circuit. (S.lg)
ISection 3.12.3]
Q. 2 Exptain with neat sketch the working of sequencing
circuit for the two double acting air cylindels.
[Section 3.12.2) (W-l,r)
3.16 AylchroDLd.ag Cltcult

Q. 1 Explain with neat sketch tbe worLing of motion

synchronizatioD circuit with the help of flow divider,
to control the movement of two double acting
cylinders. (W-f4)
3.r8 Eydradtc AtsDcr Cksutt
Q. t Elplain with neat sketch, working of hyalraulic
shaper. (W-11)
OR
Q. I With the help of neat circuit diagram, explain the
tunctioning ofhydraulic shaper. ($14)
@l ,t, rr"u-tt 359 O I Hydraulic Cncuits

3,ta Eydrsufk lfifuDg Ueahho or Eyalraullc Surf..e

crLrdLug Ue.hlao
Q. 1 Draw a hydraulic circuit diagram ior milliog Eachine
to control its table movement. (S-12,S-13)
OR

Q. 1 Explaitr with neat sketch hydmulic ctcuit for milling

machiBe. (W-f 2, W-r3' w-14)

a.1a tcgrttorrtlvo clr.Gult

Q. I What is regenerative hydraulic circuit ? State aJly two
applications of it. ($fS, W-13)
4.19 Eydrsulta Ctrsult loi Fsst Approaah, Slor Cutttrg .nd
Fsst R.turn of Urohllo T.bl.
Q. 1 Draw and explain hydraulic circuit diagra$ of a
systcm haviqg DAC which has rapid approach. Slow
speed and mpid returD. (W-r2)

4.9() Irud Pulup Eydraufto Cfrcult

Q. 1 Explain the circuit for high-low double pump system
for punch preBs application. (S,fl)

3.2? EydButlc Tta6 Dol&y Valve Clreutt

Q. 1 Wh6t is time delay circuit ? Explain any oDe time

delay cirtuit. (W.l,r)

oru
ffi ,r, (r""r.) 3-60 OLlHydla!lic Crrcuils

Note
Chapter

lntroduction to and ComPonents

of Pneumatic SYstems

Sfllrbu!
. Applications of pneumatic systems
. General layout, merits and limitations of
pneumatic
sYstems
. Selectlon of alr compressors for pneumatic circuits
. Valves
Construction, prlnclple of working and symbols
of

Pressure regulating valves, Direction control

valves'
Flow control valves
. Actuators
Construction, working and symbols of
Rotary Actuators - Pneumatic motors
Linear Actuators - cylinders - single acting, double
acting.
. Accessories
construction, working and symbols of Pipes' Hoses'
fittings, FRL unlt
Eff,tt 1, 4-2 lnirod.lo & co of Pneu. Sys

4.1 lntroduction:
Pneumatic system is a power transmission system in which,
transmission ofpoEer takes plac€ tllrough comprcssed air.
Power is giyen to coEpressor. Cohpressor ilraws the air liom
atmoaphere, compr€sses it to higher prcssure atrd stores the
coEpressed air i]! the air receiver tank.
Compress€d aiillows tom the air receiver tank to the
actuator (cylinder or motor) where mechaDical x,ork output
tu obtained.

4.1.1 General Layout of pneumalic System :

s-m1t
o. Draw and explain general layout ol pneumatic system

w_20r1, w-201s, s_2014

o. Draw general layoul of pneumalic systom and tabot the

ooubre ading c-ytind€r

wdh rntsgrat

B
42 Oireclion

T
!
ii

Fig,4.l.l
lQ) re t MSBTE) 4-3 lntrod.to & Compon. ol Pneu. SYs.

4.1.2 Components of Pneumatic System :

w-2012
O. Name the components ot pneumatic system. What are the
lactors to be considered while selecting them?
w-2013
O. List out main elements ol pneumalic system.
,l
Ail compresaor :

It draws the aii fiom atmospher€, compresses it and deliveE

compress€d air to the pneumatic s)'stem.
2 AIr dry.r :

lhe compressed air delivered by the compressoi coDtains

moisture ftom atmosphere Tlus moisture is separated and
removed by tie ai dryer. Only the dry comprcssed air is
given to the pneumatic sYBtem.
3 Alr recelvsr tank I

It stores the compresaed air. Apan from storing the

compress€d sir, it has several other fuuction also. It acts as a
cooler to cool the hot comPEssed air. It acts as a moistule
s€paiator to separate and r€move water contsined in the
cornpr,essd air. It acts a.s a support to dou[t complessor
and other componetrts.
4 FRL unlt:
It is a combination ofthree difrercnt udts.
Air filt r filters and removes dust particles from
compnessed air, aad sllows clean alry compressed air to the
system,

Air rogulator controls the pressure of cooPressed air'

Air lubricator adds lubricating oil to the compressed air'

@f,r" luser.y 4-4 lnlrod.to & Compon. ol Pneu. Sys.

5. Dliectlon control valvg:

It controk the direction offlow
ofcompressed air, by which it
p€rforms extenBiod and retraction of the actuator (double
actiry cylhder).

6. Flow conlrol valw :

It controls the rate offlow ofcompressed air, by vhich, spe€d

of extension or r€tractiotr of the actuator is controlled.

7, Double acting cyllnder :

It is a litrear actuator. It develops force atrd motion.

Force developed = Pressure of compressed air x A.rea of piston.

F A durilg exteosion
= p,/
F = px(A-a) during rehaction
4.1.3 Factors to be consldered whlle Solecting the
Componenls ol Pneumatlc System :
. Operating pressure ofcompressed air
. FIow rute ofcompressed air
. Filts ratings for selection offilters
. Stroke lengtl requircd for selection ofcylitrders
. Force r€quired artd speed r€quir€d by the actuat r-

. Compatibility, durability, cost etc-

. Port size, pip€ size etc. ofconnections.
. Envfuonmental conditions such as temperatue, humidity

. Surrounding conditions such as chemical, high temperature

B,FP ,MSBTq t't l"'
/t-1.4 Advantages ol Pneumatlc Systema :
w-m12
O. What aro the modts ot pneumaiic systems?
w-2013
o. List any fotrr mgdts ol pneumatic systems
92014
List aiy thr€e rnoritB ol Ftoum& systgm with rrsSotlino
o.
w-2a|14
?
o. What are lhe
Pneumatic syst€m.s are very fast in
op€rstion This is
1
air'
because ofvery low viscosi8 of compress€d
for longer period'
2 Pneumatic systeDe csn rrm continuously
pneumatic aystem'
"Harder it runs, cooler it workB' In any
the continuous free expansion of comptessed
air causes
lon8 run will Dot heat
chilting efrec. Due to Ois, continuous
the systelo components'
Pneumatic s)'ste6s worLB better even
in hot surroundingls'
sJrst€ms ale coot on duty even in
very hot
,:1" oo.o-",i"
suirouDdings of about 125'C'
they do not
4. heumatic syst€m.s arc b€tter in Eioes Because
g.n""tt" t ri hence !o chaDce of explosioo and fire
"p"tf ".oal
hazard
duEt ftee
Pneunatic slEtems ane very cleatr' abGolutely
surroundings.
6 PneuBatic BysteEE at€ eEvironment frieodly
The

compressed Eit cao be erhausted

to atmosphere {rithout any
harm.
siEpler'
1 Betuitr lines are abseBt, Baking the circuit
8 I-eakage of comprcssed air do€s trot pose any probleln' except
a leductioB io effrcreocy.

I Ifoverloaded, the system stalls slstem v'ill start worLhg

once the load is reduced'
possible'
10 Autooatic anil safety circuits are
 E,r" 1r""r. 4-6 tntrod.to & com Pn6u. Sys.
4.1.5 Disadvantages (Limitaiions) of pneumatic
Systems
s-2012
o. What are |he timiiations ot pneumatic
system?
s-2014
o. Lisl any thre6 demerits of pneumatic
syslem wilh reasoning.
w-2014
o. What are the ot
I Force-developed by pneuDatic syst€m
is very less coEpsred
to hy&aulic systcms. l,his is tlecause;
the air is compressible
in natur€_ Air pressure can not be iucleased
t hiSh value.
Generally, a pressure up to 10 bar is used_
2 Ai is fr€ely available in nature, but aot the
comprcssed air.
The compressed air is very cos y. This
is due to the various
losses of eDergy during comprBsiotr (such as
heat of
compression, frictional loss, lea.kage
losses etc.).
CoEpressed air shculd be used with much coocem, should

3 Lubricat r is requircd, t! add lubricant oil

to compress€d air
aDd to hiniDdze friction

I Pneumatic systenrs a.r€ noisy unless

the exhaust ports are
fittcd with silenceB (mufllers).
5. Precise coDtrol ofspeed is not possible.
This is trecause oflow
viscosity and fast hotion of air into the
cylinder.
4.1.6 Appllcatlon3 o, pnsumauc Syltems :
l PDeunlatic tools : &illing machine,
driver, nut
runner, jack hamner etc.
2 Pscking syst€hs : pacting is the 6nal operstion
dotre on
the product in sDy industry. packing should
be as fast as
possible. Almost all packing machiDes
arc ptreumatic
systems.
 iMSBTE) 4'7 lntrcd.to & Compon. of Pneu

3 Mltarirl hsndting and robotics : clamps, conveyors,

count€rs, mbotic aima et{.
4_ MiiiDf : due to iDfladlmabte gasses evolve fioE earth
during mining aod due tD the pres€trce of explosives in the
minB, etectrical devices should trot be us€d, b€caure, the
spark produced by them may cause explosion and fire
hazard. Hence, pneuaatic hand tools are ext€nsively
employed in mines.
Autonobiles : Air bmke, Air suspension, automatic doors'
wipeE, cuEhions, etc.
6. Mechine tools : Ptreumatic pre$, Pneumatic dlilling
EachiDe, clamps, vices, etc.
7 Medicgl and deatal equiPEents : deotal chair, opemting
table, dentsl drill, et .

8 Agticulturol cquipments : Shears and Prurdng Machhes'

4.1.7 Selsctlon ol Air ComPrsssor lor Pneumallc System:

Following factors are to be considered white selecting air

cotnpnessor for a Pneumatic 3,Btem.
l. Avcrags air consuEption of the systen : Ait comprea6or
should be s€le€'tpd of capacit 2 to 3 times the average air
coBumptioD of the sy8tem.
2. Free air delivery : Capacity of coDpt€ssor is epecified by
FAD.
FAD ie defned a.s volume of air drq$n by the compnesaor per
unit time. Afte, compiession, the voluEe reduces as per
pressune.
U Qr ie volume low rate of aL drawD into tlle compressor' Pr
is atmospheric Pre6sure.
compressor,
Q, is the volume and flow rate of arr delivered by
P, is delivery Pressure.
PeQz
lhen, fAD = a, = -T;
trP IFP (MSBTE) 4-8 lnlrod.to & Compon. ot Pneu. svs.

B. Air receiver capsciq/ : Volume of air rcceived

should tsrl
be greatsr than the volume of compreesed air delivered bv
the compressor in 1 ninut€.
4. Power supply : If electrical motor is us€d, then wattage,
speed, phase etc ar€ to be coDEidercd.
If IC engine is used, then hp, speed et . are to be coDsidercd.
6. ConllgurEtioD:
. Tank mounted or base nounted t,,p€
. Simplex or Duplex t ?€
. Beciprocating type or mtsry type
G. CotnlroneDb end accessories : Pressur€ switch, rclsJ,s,
thermoststs, pressure gaug€, dr&iD plu8 eta.
Remembor - "compEss€d alr i! vety costy,' :
. Air is fre€ly available, but not the compressed air.
. CoDpressed air is very costly due to various.pow6r los€es?
during compEssion. Main loss is due to .h€at of
coEpression,.
. During compr€ssiotr, pr€ssure will increase, volume v{ill
reduce, and temperatu& will incrrease because cohpression
is not isotherEal, it is polytmpic compEssion. A mqior psrt
of supplied power g€ts convert€d iato heat energy. This heat
is dissipat€d t atmospherc, atrd hence, theE is loss ofpower
in the form ofheat.
Conserve lhe Compresrod Alr :
. Conserving the compressed air is conserving the eners/.
. Employees should be trained welt to conserve coopressd ah
in any industry.
. CompreBsed air should be used wisely, it should not be
wastd.
. If leakage of air is fourd anJrwher€, iEoediately it should be
stopped.
. Use compressed air fo! cleaning anything (usually, clotfi,
chair, table, etc.) should not be allowed.
@f,., SBTE) 4-9 lntrod.lo & svs

4.2 Air Receiver

s-2012
o. What is the function of air receiver? Explain and draw its

Air rcceiver is a storage tsnk to store the comPress€d air' It

not only stores th€ coDpr€ssed air, but abo it sc'ta aE :
. A cooler to cool the hot compr€sBed air,
. A Doisture rePeratol to separate water contaircd in
coDpressed ail,
. A drDlrer to absorb the pulsation ofPressuE in coropressed
air.
The fotlowiDg are some importsnt poiots to be considercd
while deaigaing air receiver tank.
. Xcceiver tanl nuztba tuffiaientlr large la
o Store suffcient resenre aDount ifcompressed sir'
o Cool the air. to coodens€ aDd contair wat$ until it i3
&ained out.
. nDceiver tenl mt,,sttf- ruffuigntlt,t ?.ng l'a
o Withstald the ples6ur? ofcompressed air.
o To carry the coDpr€ssor atrd othei accessories Eounted
otl it.
. RDceiver tsal Eust t:sve imlnt',o,rr, Nceazoria, sncld
aa
o Pressur€ relief valve, which opeas and leleas€s hiSh_
pressure arr to ahlosphere if t}le inside prcssure
increases above Preset value.
o Drain valve, to draitr out condeised water.
o Pressule gawe gnd temp€ratur€ gauge to measure
pr€ssure s.trd temp€ratu€ of coEpre$ed eir'
o Removable clean out dool to clean itrside the tsnk
occasioaellY.
LE trp tiasAre) 4-rO tntrod.io & Compon. ot pneu. Sys.

. llle compressedair coming out of air comprcssor is hot due

to heat of coEpression. It is stored in air receiver taok for
some time before it is taken to pneumatic system.
. By this time, air is cooled, and moisture condenses to fonn
water- Water collects at tLe bottom and calr be easily &fied
out. Automatic draitr valve is usualy provided u,hich opens
automatically at preset regular intervals.
Capacity ol alr recolvBl
Capacity of receiver means the volume of the receiver.
Receiver taak frlrt tE sufrriently large to storc sufrcieDt
r€serve anount of compressed air ard to cool, condeuse and
contai[ water until it is dreined out.
Capacity of air receiver (or volume oI receiver tgnk) should
be greater thar volume of compressed air prcduced itr one
minute
AtmosDheric pressure x FA-D D€r minute
Capacity of air rcceiver >
Pressure of compressed air
Symbol ol 6lr recelver :

trig.4.2.1
4.3 FRL Unit :

s-2t 12
Q. What is FRL unit? Explain its function.
iN13
O. Whst is moao by FRL unit ln pnoumatic circuits and siate th6
ll.inclion of each.
w-2013
o. What is FRL unil? Explain its working with symbot.
w.20't4
o. lain tunction of FRL unil with neat sketch
ffi IFP (MSATE) 4-11 lnrrod.to & Compon. of pneu. sys.

FBL unit is a deyice cotrsisting ol Air Filt€r, Air Regulator

and Air Lubricator. It is also catled air serviciDg unit, because it
do€s the tunctions of cleaning, pressure 6dju6tment ard lubricating
the compreased air.

Functlon! ot FRL unlt i

. Air filtar : It seF,arates solid contaminatrts froDo compressed
ah ard provides clean air to the pneumatic 6ystem.
. Air regulator : It is a pressule rcducing valve. It maintains
comtsnt rcduced plessure iD the pneuDatic system.
. Air lubricator : It sdds lubricating oil to the flowing
compressed air in the form of mist or fog.

+ ! I

Symbol ot FRL unit :

i'is. .1.3.1
lcPl rFP 4-12 lnlrod.to & Compon.

4.3.1 Ah Filter:
. It s€parates solid contaminants from coopressed air a[d
supplies clean air to the pneumatic sFtem.
. Air filter is shown in Fig 4.3.2. Air €nteE the hansparent
bowl through the inlet. It Passes throwh the filt€r eleoent
towads the ceater, and flows out thmugh tlle outlet lhe
filter element is made of Eintcred powder of copP€r, braas,
brotrze, glDn)et3l et .

+ .+

Fig.43,2

. Fibmu,s coalescence frlter element can be used to r€Dove

moisture in comPressed sir.
. The moisture droplets stick to tie fibels Joining of s€veial
moistuie drcplets makes the liquid to gain msss a[d hetrce it
flows down due to glavity.
4.3.2 Alr Regulator:
w-2012
o. Draw and label air reglilalor.
s-2013
O, Explain with neat skelch tho construction of non relieving
pressure regulator.
lFl,'" E) 4'13 lnlrod.io & Compon. u. svs

AiI iegulatDt is a pressure reducing valve. lt mahtains

constart rcduced pressure iD the system.
Air re8ulato! is shown in Fig. 4.3.3.
When pressure at outlet iscreas€s, diaphragm deflects
downwards, aDd causes the poppet to close the paesage for
air flow.
Similarly, when pressure at outlet decreases, diaphmSm
deflects upwards, and causes the poppet to make pasaage for
air flow.

Il& 43J
ID csse, if the pressure is too hi8h, that, eveD aft€r complete
closure ofthe passage, pressule do not comes to trormal, then
t}re diaphragm dellects dowItward causing the hole iD the
diaphragm t open, to rclease air to atmosPhere thrcugh tlre
vent holes.
4.3.3 Air Lubrlcator
w-2t 1,
O. Explain wolking and conatruc-lion ol lubricator.
s.?o'2
O. How fine spray or atomized spray ol lubricating oil is obtained
in lubricaior of FRL tinit.
w-2t12
O. Draw labeled sketch ol air lubricator.
ffi IFP (MSBTE) 4-14 lnlrod.lo & Compon. ot Pneu svs.

Air lubricator adds lubricating oil to the flowhg compressed

air in the forrn ol mist or fog.
Lubricating oil i-s necessarJ' to reduce friction betweeD
moving parts in ttre system.

Ajr Iubricator uses the principle ofvetrturi effect.

I O-ring

Fig.4.3.:l

Accoding to Bernoulli's theorem, if the area of flow is

reduced, then prcssure reduces ard velocity iDcreases.

The transpsrent bowl coDtains oil iI! it. Due to the difference
in pressure between iElet and throat of venturi, oil is forced
to flow hto the tbioat.
Oil get mixed up with the compr€ssed air and carried to the
different parts of the systeE.

An adjustmeDt scr€w is there to coltml the flo]v of into the

system.
ffi,t"t, 4-15 lnlrod.lo & Compon. ol Pn6u. Sys

4.4 Condensation of Water:

9?013
O. Stal€ the functions ot moisturc separator
s-14
O. Enlist the probledE encouriered due to moisturo condensalion
in pn6umatic syst€m. Narne the ditferenl types of air dryers to
avoid moistuB condensation.

Atmospheric air ha.s Eoistul€, and this air is coEpr€ssed

and used in pneumatic systems. So compressed air also has

If the t€mperature faUs, thed the moisture coodens€s to form

wat€r. If there is tro Eoistur€ separator, then, ,eceiver tank
will be tuIl with wat€r withio a few hours.
(In poeurDatic sJ.stems, temperature falls due to preseure
loss in pip€s, and free erpaosion of air in pipce, valves and

The condens€d Fater creat€s lot oftroubtes in the pneumatic

sy8teD.
o It creates disturbance t, the flow of air.
o It ofmetsl surfaces.
causeE corrosion
o It combiDes with impurities such as oil, dust €ta. to
form gel or varaish which clog the ports ofvalves.
o It may fieeze to form ice.
Heoce to avoid these diftculties, moisture from the
compnessd air should be reDoved befor€ it edters the
rcceiver tank.
For tiiB purpose, moisture s€parator and air dryers are used.
4.4.1 Moistur€ Separator :

It is used to separate and rcmove moistu€ from comp.essed

air. lte compressed air is made to pass through rediel
multi-nozzles, due to which, it starts s$r'fuling with hiSh
velocity iDside the bowl a.s sho{,n ia Fig. 4.4.1.
ffi,r, tr""t.) 4-16 lntrod.lo & Compon. ol Pneu. Sys.

Due to swirling, centrifugal force is induced in moisture

drcplets, which causes the moistur€ droplets to move away
fiom centre tovrards the eall of the bowl

+ + Oullel

Radialmullr

rat
Drain plug

Ii8.4.4.1
. At the wall of bowl, these droplets joins together to Sain
mass. and flows down due to gravity. Watet collected at the
bottom ofthe bowl can be removed easily

4.4.2 Coalescence Element Type Flller:

!

+
lnlet
+ Outlet

Filter element
(Fibers)
ffi ffi

Drarn p ug
l'ig.,1.4.2
@,rt 4-17 lnlrod.to & Compon.

. Corlescence meaos joining of tioy moisture droplets of

negligible mass to form bigEer liquid droplet of considemble
maaa.

. The coalescence filter element is made ofEicro'fibers'

. When comprcssed sir is pa.ss€d through the 6lter element, it
passes over the micro_6bers. The Eoisture droplets stick to

the 6bers.
. Joini[g ofseveral moisture d.roplets makes tbe liquid to gain
mass and hence it flows dowtr due tD gravity Wattr collect€d
at ttre bottoD of the bowl can be removed eaeily

4.4.3 Alr DrYoE :

. ltlere ar€ two main typea ofair drl'ers, they are :
o Refrigerated air dryer

o Cheuieal air dryert

(a) Detiquescetrt air dryer8
(b) Absorption air dryers

4.4.3.1 Rolrlgoratsd Alr Dryort:

. In refrigersted sir dryers, refiiSeration gysteE is used to cool

the coEpressed air'
. Whea compreseed air is cooled betow certsin poitrt, moisture
condenses to form liquid water.
. llre coniletrsed water flows down due to gravity and gets

colect€d at the bottod ofa t5nk.

. The collectad v.at€r is drained out rcgula'ly u8ing watcr traP
(automatic dl'ain PluB).
ffi,r, (r.u* 4-18 lntrod.lo & Compon. ol pneu. svs.

4.4.3.2 Chemical Air Dryers

A) Dellquescent Air Dryers :

. In deliquescent air drye$, compressed air is passed

through a bed of chemical crystals (salts).

. The crystals absorb moistule and fom a liquid

solution.

. This solution flows down due to gravity and gets

collected at the bottom of the dryer.

r The collected liquid solution is dmined out rcgularly

using water tlap (automatic drain plug).

. Salt-based crystals and urea-based crystals arc

generally used as deliquescent.

B) Absorptlon Air Dryers :

. In absorption air dryers, compressed ai is passed over

absorption material.

. The absorption material collects the moistwe particles

and retains in it.
r It allows only dry air to pass through.

. Absorption material does not dissolve with moishrre. It

gets wet and soaked with water.

. The absorption material can be regenemted if it gets

tul with watsr, by rcheatirg and can be reuseil.
. The chemicals used in absorption air d:ryers are
activated alumna, silica gel or both in combination.
ffi IFP (MSBTE) 4-19 lnirod.to & Compon. ot Pnsu. sys.

4.5 Control Valves

. In pneumatic systems, we use "compressed ai/ t perform
specific tasks such as lifting, pressing, cutting
et .
. For doing the above said te.sts, we have to .ontrol tbree
importad "work Darameters".
They arc
1. Arnount offorce applied
2. Speed ofdoitrg tie work
3. Diroction of applicstioD offorce.
. For contmlling the above said "woik psramet€ru", we have to
cotrtrcl tbree differ€nt "comprressed air parameters"
They are
1. Pressure of compreseed air
2. Ret ol f,or of comprcssed air
3. I)ir€ctio! ofltov ofcompressed air
. For controlli-n8 the above s6id "compressed air psr.anetcrs",
tfle use tbiee diffetcat 'control velvor".
r Preesure C,ontrol Valve (PCV) coatrols the pressur of
compressed air, by which we csn control the force developed
by the actuator.
Duritrg ext€D-sion,
p = pxA
and during retractio[,
F = px(A_s)
. f'low Control Velve (FCV) controls the llow rate of
compness€d air, by which we caD cotrtrrol ttre speed of
actuator.
During exteDsion,
..q
' -A
atrd durin8 r€tractioB,
o
' - A-a
. I)iDectioB Conhol V.Ive o)CV) coDtrols the diiection of
flow of compressed air, by which we can codtrol ttre dfucction
of motion of the actuator.
El",', 4,20 tnlrod.lo & com

4.5.1 Classiticatlon ol Control Valves

(a) Accordlng lo function :

1. Pressrre control valves

. Reliefvalve . Reducing valve

. Sequence valve
2. Direction control valv€a
r Check valve . 212\alve
. 4/3 valve ' 5/2 valYe

3. Ilow control valve

. Fixed Restrictior FCV
. Vaiiable Restriction FCV
. FCV with Revelse FIee Flow
. Ca]n operuted FCv

(b) According to the method actuallon :

1. MaDuaI operated
(a) Palm oPeraed
(b) Push button operated
(c) Hand lever oPerated
(d) Foot pedal operated
(e) Cam (roller) opemted
2. Pilot operat€d
(a) Shgle pilot
(b) Double Pilot
3. Solenoid operated
(a) Single solenoid
(b) Double solenoid
 (MSBTE) 4-21 lntrod.lo & Compon. oJ Pneu

(c) Accordlng to construc on :

1. Poppettyp€ : Ball t T€, conical poppet tvpe

2. Spooltype : Siding spool t}?e, mtary spool t]'"e

g. Flowcontrll: Gate valve, plug valve, needle
valwe' PoPP€t valve, butt€rIlY
valve etc.

Valve! atrd actuators are exactly similar for hydraulic

syst€ms anal pneuEstic systems in coDstructiotr and fuDctioning'

Only the difrerence is, hy<lraulic compoDetrts are made

stmnger anil hesw, they are made of steel, because, they have to
work under very high Pressure of oil. PtreuEatic componenta are
ma<le of lighter using aluminum, plastic et because the
prcssure

of compr€ssed ai! is just about 5 bar.

4.5.2 Fac.tors to be con3ldsl€d whlls salectlng control

valv63 :

Fotlowhg factors should be coBidered while s€lecting

control valve8

1. Flore rate ofcomPressed air

2. Pressure ofcomPEssed aL

3. Fotce requircd bY cYlhder

4. Speed ofoPeration ofcylbde!

5. lype ofactuatioa ofthe valve

6. Port size

?. Space EquiremeDt

8. TeBperatu€ of coDPress€d air

@) re SBIE) 4-22 lntrod.to & Compon_ ot pneu svs

4.5.3 Pressure Control Valves :

9201'
O. Stale ditferent types (any 4) o, pressure conlrot vatvos with
their applbations.

Diferent tasls deEand alifrercnt aEount of force. To lift a

chalL and to lifi a rock, the forces are rot tlrc same.

IE hydraulic machines, it is dec$sary to control tf,Ie force

generated by the actuators (cylinder or r totor).

As we know, forre of cylinder is the Foduct of pnssurc of

compressed air and area of piston. F = p r A

To vary the force, we need to vary aay of these two, either

the pressure of compressed air or the area of piston.

the size of a cylinder i6 fixed; we can't have any kind of

valve t, var.y the size of a cylinder.

But lve caD easily vary the pressure of compr€ss€d air by

using a pressure control valve.

PIessur€ cotrtrol valves are used to coitrol the preesure of

compres8€d air by which, we catr codtrol the foEe developed
by the pBeumatic actuator.

IlEre ar€ va.rious t)'ps ofpressure contml valvee

o Pressure reliefvalve

o PressuE reducitrg valve

o Sequence valve
@'r, MSA 4'23 lnlrod.to &

4.5.3.1 Pressure Reliel Valve :

w-2tt12
O. lrrhat is lhe function ot prossure reliat vatve? Where it is
located? Skolch direct op€Eting prossure rstiet vatv6.
9nt14
O. With a n€at skstch, explain the lunclioning of simple prcssure
rali€f velv6
w-4)11
O. Expialn pressure relief valvg us€d in pneumatic systom.

It's functioning is similar to the relief valve of a pressure

cooLer of our Litchen.
If pressue inside the system incieas€s above pre-set level,
thi.s valve opens to Elease the air to atmosphere, so that the
sy8tem pres8ure comes to trolmal.
Cdi(, popp.l I

!I\\r
Spong

Fig.4.5.l
Relief valve consists of an adjusting screvr, two supportiDg
plates on either side of the sprint, and a conicsl poppet
which are mounted inside the valve bodv as shown in the
Fig.4.5.1.
When ttre pressure at iElet increases above pre-set limit, the
conical poppet moves inside against the spri[g force, and
creates a passage for comprcssed sir to flow to outlet.
ID paeuDatic systemE, the outlet of relief valye is op€n to
atmosphere, so that air is exhausted to atdospherc-
Once the pr€ssue comes to normal, the conicrl poppet sit
back in it€ positiotr on the seat, clos€s the passag€ from inlet
to outlet.
W BTE) 4-24 hlrod.lo & Pneu- Sys.

4.5.3.2 Pressure Reducing valve (Pressure Regulator) :

s-2011
O. Draw and explain vyorking ot paessure reducing valvo.
w-N11
O. Explain with neat skelch wolking ot directly operated pessure
reducing valve-
w-Nl4
O. Explain the workang of pressure regulatol vith neat sketch

=
,,
=
SpnnS

It9.4.5.2

Prcssure reducing valve is used to maintair con8taDt

reduced Fessure in the s,'stem. It has atl adjusting scr€w, a
spring, a conical popp€t fitt€d to a diaphragD a.s shown in
the Fig.4.5.2.
Ifthe pr€ssure at outlet 'O' increases, the diaphragm defects
upwards, due to which, the conical Poppet will aleo move
upwards to close the passage of eompreesed air flow. tltus
the flow reducea and the pressure Educes to normal.
Once the pressule coEes to normal, the diaphragm deflects
dowowards and the conicrl poppet moves downwards aad it
opens the passsge for coDpressed air to flow.
This valve iB cslled "pr€sure rcgulato/ i.tr pneuEatic
systems.
ffi,., (r"rrr) 4-25 lnlrod.lo E Compon. of Pneu. Sys

4,5,3.3 Sequsnce Valve :

. Sequen@ valves are not that much popular in pneumatic

systeds b€cause, pressure raDge ofcoopress€d sir is usually
0-5 bar. Within this shall prcssur€ range, it is difrcult to
adjust the crackiBg pr€ssure of sequeDce valves.
. Sequence valveg are extemively used in hydlaulic syst€ms.
. In pneusatic systems, sequencing of operatioos is done with
the help ofeither'pilot valves and limit valves" or "solenoid
valves and lioit switches".
. But, as a part of study, sequence valve for pDeumatic sjastem
is explained below.
. SequeDce valve has an adjusting screF, a spring and 6
conical poppet, which are, mounted iDside the valve body as
showD itr Fig.4.5.3.
. It has oae inlet port and two outlet ports, outlet port "1" aDd
outtet port "2".

=
-=
SpnnO

I
= 2

Rg,4.5J
WheD compressed ai, is supplied to inlet port of sequence
valve, it flows directly to outlet port'1". Hence, firut cylinder
extends.
By completion of ext€nsion oI first cylinder, pre$ure in the
line inc'rcases and heace the poppet of sequetrce valve lift€ ofr
from its seat and allows compressed air t fiow to port "2",
henee cylinder-2 ertends.
[ff,r" 1r""r.1 4-26 lnlrod.to & Compon. of Pnsu. Sys.

Thus, sequencing is achieved between the two cylinders.

Sequence valve ca]x allow compressed air h reverse diEction

Iiom port '1". But it does not allovr/ reverse flow fiom port
"2". Retmction of first cylinder is possible, but retraction of
socond cylinder is not possible.

Hence. a check valve is essential for reverse free flow of

compressed air from cylinder'2 to atmosphere, lor rctraction
ofsecond cylinder.

Gercrally sequence valves come *ith integrsl chcck valv€ as

shown in Fig.4.5.4.

Sequence valve wllh

lntegral ch€ck valva

lig. {.5.{

Nol€ : Refer Soction 5.12 for circuil.

4.5.3.4 Pressure Switch :

It k an electrical switch, which is operated due to piessurc of

fluid. When compressed air pr€ssure exceeds the preset
value, this swit{h brea}E the electrical contact with electric
motor, so tie motor is tripped off. Thus the compressor stop6.
Pressure swit{h is a salety device; it avoids development of
over pressure aIId preveots the chances of accident6.
ffi,r, rr""r.t 4-27 lnilod.to & Compon. ol Pneu. Sys.

4.5.4 Direclion Control Valves :

Direction control valves aI€ used to control the aliectioo of
flow of lluid, thereby to control the directioa of aovemetrt of
actuator.
For extensioD or retractioD of cylinder and for clockwis€ or
snti-clockwise rotatioB of motor, we need to change the
direction of flow of fluid, which is done by dircction control
valves.

Classllication ol diroctlon control valyes :

A) Accordlng to the method actuallon :

1. Manual operated
(a) Palm operated
(b) Push button operat€d
(c) Hand leve! operated
(d) Foot pedal op€rat€d
(e) Cam (roller) operat€d
2. Pilot operated
(a) Single pilot
(b) Double pilot
3. SoleDoid opcreted
(a) Single solenoid
(b) Double soleDoid

B) Accordlng to typo ol Epool :

l. Poppet t T€
2. Sliding spool type
3. Rotary spool type

C) Accordlng lo number ol ports and posltlons

Che.k,ts,l\e, %2, 3/2, 42, 413, 512 eto.
ffi,r, (rs"r.) 4-28 lnlrod.to & Compon. of Pneu. Sys.

4.5.4.1 Check Valve

s'2t 12
o Explain wofting ol di.ectly op€rated check valvs with neat
sketch.
w-2lt1g
o State the tunction of check valve in pneumatic circult.

Check valve is a uni-directional

valve (non-retrrrn valve), which
allovrs compressed air to flow in
only one directiotr. It will not
allow compressed air in othe, B
direction. Fig. 4.5.5 shows a
check valve. It has a spring-
loaded ball or conical poppet
inside the valve housing.
When compressed air is B
supplied to port-A, it exerts
pressure on the ball against the
spring force; hence the ball will
be lifted otr from its seat, and
creates a passage for air to -+-
floq,. Hence compressed air can
flow Iiotrt port-A to port-B. Fis.4J.5
When compressed air is supplied in opposita directioD, that
is, to port-B, it forces the ball to sit firmly in its seat; hence
the passage is closed by ball. The coopressed air cannot {loq/
from port-B t port-4.
Check valve is an important valve, which finds application itr
many circuits for obtaining reverse free flow. In otre
direction, comprcssed air has to flow through flow coDtrol
valve, sequence valve et . snd in the other di-rectiotr it should
be fiee flow. Itr such case, a check valve is coDrect€d parallel
to the rDain valve.
ffi,r" (r""r.) 4-29 lntrod.lo & Compon. ot Pneu. Sys

4.5.4.2 212 Dlre€lion Control Valve :

This valve has two porh and two positions oI spool. The two
ports are inlet port-A and outlet port-B.

Sllding 8pool typ€ 2/2 DCV :

. The Fig. 4.5.6 shows a sliding spool spring retum type
Norrually Closed Z2DCy.
r ln normal position of the spool, the ports are closed;
cohpressed air cannot flow from port-A t port-B

. 'When the palm buttoD is pressed, spool moves to open the

passage flom port-A to port-B and hence coEpressed air flow

from port A to port B.

I )

fig. t.5.6
lg] tFP (MSBTE) ,t-3o lnrod.to E compon. ot Pnsu sys.

Rotary spool typo 2/2 DCV :

s-2t 13
O. Explain the wo*ing of rotary spool type valve with ngal skelch.

I'he Fig. 4.5.7 shows a rotary 6pool type Z2DCV.

In 6lst positioD of the spool, the ports ale closed; compnessd
air cafiot flow from port-A to port-B
When the spool is rotated thmugh 90o, it opens the passagp
fiom port-A to port-B and hence compreseed air flow ftom
port A to port B.

oulel B

Spoo

In el-A

Fi8. ,1.S.7
ffi,." 1rs"r.y 4-31 lnirod.to & Compon. oI Pneu. Sys

4.5.4.3 3/2 Oirection Control Valve:

s- 12

O. Draw a neal sketch ot 3y2 O.C. valve. Explsin its wo.king.

w-2013
O. Draw sketch ol3 x 2 DC pneumatic valve, explain its wo*ing
*mr4
O. Sketch the two posilions of sliding spool type 3/2 DCV and
explain in briel..

t}lis valve is used to operate shgle acting cylinders and

unidircctional motors.

It has tbr€€ ports aamely, inlet port 'P", Cylinde! port "4"
atrd exhaust port "T'.

32 slldlng spool valve :

. the Fig. 4.5.8 shows palm butt n op€ratcd sprin8 return

t}?€ 3/2 slidiog spool valve. It has a sprirS-loaded spoot
inside the valve My. In figur€, it is palm-operatcd twe of

. ,2 valves are used to operat€ sugle acting cylinders.

. ln spool position as shown in Fig. 4.5.8(a), there is

connection from port-P to port-A. Compreesed air flows to
single actinS cylinder. heDce the cylinde! extends. The
exhaurt port-T iB closed.
. In spool position as shown in Fig. 4.5.8$), there is
Air flows from sinSle acting
cooDection from port-A to port_T.
cylinder to atmosphere hence the cylinder rctracts lnlet
port-P is closed.
ffi,.t tr""r.t 4-32 lnlrod.to E Compon.

I
PT
(D) -
Fis.4.5.8

3/2 roLry spool valve :

. The Fig. 4.5.9 shovi,s a 3/2 rotary spool valve. It hss rot ry
spool iNide the valve My. The spool is rotat€d through
l20o to op€rate the valve.
. In spool positiotr as shown in Fig. 4.5.9(a), there ie
connection from P to A. Compressed air flows from
compressor to single acting cylinder. Hence the rylinder
extends. The atmosphele port or exhaust port, that is, port-T
is closed.
. When the spool is tumed to 1200, that is, as shown in shown
in fig. 4.5.9(b), there is corllection from port-A to port-T. Air
Ilows from single acting cylinder to atmosphere. Hence the
cylinder rctracts. The inlet port port-P is closed.

T
(b)
fig.4.5.9
ffi,r" lust-.y 4-33 lnlrod.to & Compo

4.5.4.4 4/2 Direction Control Valve :

s- 11

O. Oraw a skolch ol normal and actuated po6ilions oI 4f2 OCV .

!t4014
O. Sketch lhe two positiohs ol rotary spool type ,t/2 OCV and
explain in briet.

Thb valve is used to operate double acting cyliadem aod

bidiEctiotral motor6.
It hss four ports traeely,
o Cooprersor port or inlet port "P',
o Cylinder port "A",
o Cylinder port "8" aad
o ExbauEt port
.r,.

l T

,U2 slldlng spool Yalve :

o The Fig. 4.5.10 shows spring retum typ€ slidiog spool valve.
It has a spring-loaded spool inBide the valve body. In
Fig. 4.5.10, it is palm-op€rated tlTe ofvalve.
r In spool position as shown in Fi8. 4.5.10(a), there is
contrectioD froE P to A and B to T. Compressed air llov{s to
cap end port of cylinder and comes out from rcd end Port
Hetrce the double acting cylinder extends.
r When the palrn buttotr is pr€ss€d, the spool pGition is as
shown to Fig.4.5.10(b), there is connection from P to B and
A to T. CorBpressed air flows to rod end port of cylinde, aDd
comes out from cap end port. Hence the double acting
cylinder retracts-
fl tre lusertl 4.34 lnrod.lo & Corrpon. ot P4eu Sys

I I l

I I

(b)
Fig.45.10
4/2 rotary apool valve :
. The Fig.4.5.11 sholvs a !U2 rotary spool valve. It has mtary
spool inside the valve My. The spool is rotated through 90o
to operat€ the valve.
T T

B B

(r) (b)
Its.4.s.lr
In spool positiod aB shown in Fi9.4.5.11(a), thele iE
coDnectioa from P to A and B t
T. Compressed afu flows to
cap end port of cylinder and comee out fiom rcd end port.
Hence the double acting cyliDder extends.
When the spool is mtated thmwh 90o as showo in
Fig. 4.5.11(b), ther€ is connectiod ftom P to B ard A to T.
Comprcssed air llows to rcd end port of clinder and comes
out fioEr cap etrd port. Hence the double acting rylinder
,etracts.
ffi,r" (us"r.) 4-35 lntrod.lo & Compon. ot Pneu. Sys.

4.5.4.5 /y3 Direction Conlrol valve:

92011
o E4lain 4 way 3 position direction control valve used in
pneumatic system with sketch.

I'hisva.lve is used to operate double actirg cylinder and

bidiEctional 6otor.
It has lour ports namely, lnl6l port'P",
CYinder Pon 'A'
Cylindor Porl -B" end
Erhausl Porl 'I-.
It has thiee positioD.s ofits spool.
o In first positiotr, therc is comection from P to A and B
to T, hence cylhder/motor moves in oae direction.
o In the other positioa of spool, ther€ is connection from
P to B and A to T: herce the cylinder/hotor ruls in
oppositc directioD.
o In lhe middlc positiotr of spool, lhe cylinder or motor stops, it
will no! move in any dircctioo.

AB
-Lt
Symbol of 4/3 DCV :

TT Delent
operated PT type
Closed centre
ilJ:t rlidlng 3pool valvo :
. ID first positioD of spool positioD as shown in Fig. 4.5.12(a),
therc is coDnection froD P to A and B to T. Compressed ail
flows to cap end port ofcylinde! and comes out ftom rod end
port. Hefte the double actida cylinder extends.
APAT

I t
Fig.4.5.r2(a)
ffi,." (usa-Et 4-36 lnlrod.lo & Compon. ol Pneu. Sys.

In second position of spool positioD as sho$n in

Fig. 4.5.12(b), thele is coDnection from P to B and A to T.
Compr€ssed afu flows to rod etd port of cylitrder and comes
out from csp end port. Hence the double acting cylinder
retlacts.
APST

I I
Fig.4.S.l2(b)

Whetr the spool is kept in the middle position as shown in

tlle Fig. 4.5.12(c), all ports are closed, and hence the actuator
st ps.
This is closed centre mid poaitioa.
APAI

I I
(c)
Fie.4l.l2
4/3 rotary spool velve (closod csntrE mi&posltlon) :

First and gecoad positions of

T
spool are a.s explained in 1/2
mtary valve.
Middle po6itiotr is shorn in
Fig. 4.5.13, all ports are closed, A B

and hence the sctuator stops.

This tu closed centre mid
positiotr.
l'is. J.5.13
 IFP (MSBTE) 4-37 lntrod.to & Compon. ol Pnsu.

4.5.4,6 5/2 Direction Control Valve:

w-m14
o- Explain the working ol push button operaled 5/2 with neat
sketch D.C. valve used in pneumalics, with neal sketch and its
symbol

V2 DCV is used to operate double acting cylinders.

It has five ports namely, Ir et port "P.
CYlinder Ports 'A' and "B"'
Exhaust Ports 'I1" and 'I2'
Ag

I
T1 PT2
52 slldlng spool valvo :

I'he Fig. 4.5.14 shox,s spring rctum type slidhg spool valve'
It has a spring-loaded spool ineide the valve body. In figue'
it is palm butto[ op€ratpd spring return t]pe of valve.
In spool position as shown in Fig.4.5.14(a), ther€ is
conDectioD ftom P to A and B to T2. Compressed air flolrs to
cap eDd port of cylhder aDd comes out from rod end po!t'
H€nce the double actiag cylhder extcnds
AB

I
T1 P12
fig.4.5.r4(a)

Wheo the palm button is pressed, the spool position is as

shown i.n Fig.4.5.14(b), there is.onnectiotr fi'om P to B and
A to T1. Compress€d air flowB to rod end port of cylinder and
comes out ftom cap end port. Hetrc€ the double scting
cylinder rtetracb.
[Pf,." 1r" BTE) +38 lnlrod.ro & Compon. ot Pneu. sys.

I
T1 P12
Fig.45.1(b)
5/2 rolary spool valve :
. It has rotary spool inside the valve My. The spool is rotated
through 72' to oF,erate the valve.
T1
T1
I2 J2

['i9.4.5.15

s-2014
Q. Explain why 4/2 DCV is pretefied for pnoumatic systems and
5/2 DCV pneumaiic system.

. Tlre purpose of 42 -valve and S/2 valve i_s same, that is, to
opeiate double acting cylinder.
For pnsumatic aystsmg,
. 4n va,ve is preferred. Because, it has oDly one atmosphere
port, only one retum pipe line is sufficient per valve.
. 5/2 valve is not prefented. Becaus€, it has tvro atmosphere
ports, two retum pipes are required per valve.
For pnoumallc ayst6ms,
r Pneumatic systems does Eot treed return lines, air is
exhausted to atmosphere at the elrhaust port of the valve
itselL
. 512 valve is pleferred. Because, its construction is simpler
then 192 valve (incase of sliding spool t,"e). HeDce, less coBt.
EF,tt E) 4-39 lntrod.lo &

4.5.4 7 Methods ol actuation ol DCV :

DircctioB cotrtml valves are uBed to confol th€ direction of
flow of fluid, by which, we can conhol the direction of motion
of actuator.
By shifiiIlg the spool Positior of DCV, we can obtain either
extension ;r retraction of cylinder, and clockwise or coutrter_
clockwise rotation of motor.
The spool of DCV can be actuatcd by several wavs. Some
methods are below

Lever operated

Manual
Palm button operated
H
l=
1
opeIation
Push button operated

Foot pedal opemt€d

ld
2.
Solenoid
operation
Single sotenoid
F
Double solonoid
{}

3
Pilot
ope!6tiotr
Single pilot
F
Double pilot
{}
 4-40 lnirod.to & Compon. ot Pneu.

4.5.5 Flow ControlValves :

92011
O. Whal is flow control valve?

. Flow coDtrcl valve tu used to control the lat€ offlow offluid,

by which, we caD contrcl the speed oftlE actuator.
. If flow rate of air is more, then cylitrder
compressed wil fill
quickly and hence the piston will move fa.st€r.
. If flow rate of compressed air is less, then cylinder wilt be
illed slowly and hence the piston moves slo{,Iy.
. Speed of the actuatlr is prcportioDal to the ratc of flow.
HeDce controlling the flow controls the speed of actuator.
This is achieved by flow control valves.
. therc are various t}?es offlow contml valves (FCy).
o Fixed Restriction FCV
o Vaiiable Restriction FCV
o FCV with Reverse Frce Flow
o Cam Opemtad FCV

4.5.5.1 Flxad Rsstriction FCV :

This is not a valve; it is simply a restriction with a 6mall

opening (orifice). When fitt€d in the syst€ro, the compressed
air has to flow thowh this small hole.
lhisreduces the flow rate of fluid. But it does not have any
means to vaiy the flow rate or to vary the area of flor,y.

symbor
\_-./
 MS 4-41 lnlrod.to & C

4.5.5.2 Variable Restriclion FCV :

s-2011
O, Explain non prcssure comp€nsated ffow contrclvalve'

This valve has a hand wheel, bv turdng which, we can

change the area oI flow, and thus we can cha[ge the late of
flow offluid.
OrdiDary watDr taP is a bett€r example for understandirg
the functioning. There are many types and Eatry desigDs,
exarrples ane needle valve, gat€ valve, batl valve, butt€rfly
valve, diaphragn valve poppet valve. etc

\J/
f'-

Flg.4J.r6

Fig.4.5.16 shows a treealle valve. It ha6 a neeill6, wb.rch

moves uP & down by turning the screw This alt'€rs the
passage for coDPressed air to flow, {hich inttm alteN the
rate offlow.
 4"42 lnlrod.to & Cornpon. of Pneu. Sys.

4.5.5.3 FCV with Reverse Free Ftow :

w-2arr4
O. Explain non-relurn type llow control valve used in pneumatic
system.

<F.
-tr
r.ig.4.s.t7
This valve is used to conhol the llow rate in one direction
oDly. In the other directioD, the llow is Dot contmlled, i,e.
it is
fiee flow.
By this, we can have conholled speed of actuator ilr one
dircction snd uncontrolled sp€ed in the leverce direction.
i.e. slow forr,vard stroke aDd quick rctu.in ofcylinder.
Such quick return motion is rcquired in machines like
shapers, planers, slotting machine etc.
Fig.4.5.17 shows a flow control valve with reverse fr€e
flow.
By turnir8 the screw, we can move the Deedle up and
down
to vary the passag€ for compressed air flow,
The Deedle has a drilted hole in which, spring toaded
ball is
mounted. This is check valve, and it allows coDrpressed air
to
Ilow through it in one direction only.
From port-B to port-A, it is free flow throu8h the check valve;
there is no contIol over the llow
From port-A to port-B, the flow is through the passage
crested by the needle, this is controlled flow.
ffi E 4-43 lnlrod.to &

4.5.5.4 Cam opsrated FCV wlth tntogral Check Valve

(Deceleratlon Valve) :

. If the cylinder is long, that iB, if shok€ IeDEth is mole and

the speed is high, theD naturally, the piston_ihpact oD end_
covers i6 considerably high.

. Cotrtinuous haEmering of pist n on these cover_plates

causes loosening of tie rods and leakage of fluid' A'lso it will
damage the cover Plates

. Hence to avoid sudd€n imPact of Piston on the cover Plates,

cushioning circuits are u-sed.

. Cushioning mesns "reducing the speed of piston at the etrd oI

the stroke"- That is, making the piston to eDd'up its shoke
slowly. For this purpose, special type of FCV is used which is
k own as cushioning valve or deceleration valve'
Actually it is a Cam OPerated FCv eith intzSrsl checL
valve.
Ithas a rolter, u'hich is operated by any
moving part ofthe machine.
ID tro.mal position, it has ft€e flow. When
the roller is pressed by any moving part of
the machine, the flow gets Educ€d as it
?
flows thiough the FCV. BY this, the
Eachitre table, which was fast earlier, i3
made to complet€ its stroke slowly.

It a check valve for reverse free Ilow Check valve i3

ha.s
required becsuse, the small conholled flow though FCV
aloDe cannot initiate the rcturtr stmke of the cyli[d€r'
ffi,r, tr."TE) 4-44 lntrod.lo & Compon. o, Pneu svs

(a) (b) (c)

Fig.4.s.l8

Compressed air Once the machine During

is return
flowiDg in forward table presses the skok€ of cylinder,
direction to cylhder roller of 2|/2 valve, compressed air is
through 2/2 valve, compressed air allowed to flow
hence machine table starts flowing fieely tlEough the
i6 moving in forward through FCV. Hence check valve, retum
direction with high speed of cylinder stroke starts with
speed. and machi-ue table high speed
reduces,
l!Y) rFP 4-45 lnlrod.to &

4.5,6 SPecial TYPe valves :

4,5.6,1 Tlme Delay Valve :

w-2011

o. Eiplain wilh neat sketch tho working ol time delay valvg'

I'his valve iB to have required amount of time detay

useal
extends first
between two opemtions. For examPle a cylinder
of time'
and it retracts autoDatically after Preset amouDt
Fig. 4.5.19 shows a time delay valve lt has an itr-built
3/2
reiervoir, flo*, control, a check valve, and Pilot operated
ilircctioD control valve.
port of
When the compressed at is admitted thrcugh iDlet
this valve, it flows through check valve and fils iD the
chamber, anil exerts force on the spool Due to this' the
spool

is press€d agaitrst the sp.itrg fofte, DrLing the coDnection

from port-P to port_C. The cylinder extend!'

I
,1 T

Ftg.4J.19

Whetr iDlet port iB open to compre$ed air reservoi!'

compressed air flowB through flow conhol valve
alowly back
to the reservoir' Pr€ssure in chamber reduces slowly
the
Once the pressu? becomee less than the spriag force'
port_C to
spool shifts back to make the connection betwe€n
port-T, cylinder retracts.

Note : Reier section 5.17 ,or lime circuil.

 Compon, o, Pn€u. Sys.

4.5.6.2 Shunle Vatve :

w-21r14
Cl. Exptain shulilo valve with neat sk6tch.

A shutUe valve i.s shown in

Fig. 4.5.20. "l
It has two iDlet ports, A and B
alrd one outlet port C.
It coDsists of a ball or poppet (r)
inside the valve body.
When compressed air is .l
supplied to any of the two
inlet ports, inlet port A or
inlet port B, the ball-poppet
(b)
closes the other inlet port and
compriessd sir florvs to "l
cylhder port C.
Shuttle valve has OR logic
function.
ris. 1.5.20

. OR logic function stat€ment is "\i/hen any one or Lroth of

input signals is prcsent, there will be output si8Dal".
Truth Table :

Input A Input B Output C

Yes

Yes Yes

No Yes

N0 No No
llll rFP SBTE) 4-47 lnlrod.to & Compon. ol Pneu. Sys.

4.5.6.3 Twln Pressure Valve :

. A twin pressure valve is shovrn in Fi8.4.5.21'
. It ha.s t$ro idet ports, A and B and one outlet port C'
. This vatve has AND logic tunction.
. AND logic tunctiotr ststeoent is "when both of ioput si8lals
arc preseat, then oDly tlere will be outPut signal"'
. This valve c\oD,sists of 6 spool inside the valve body WheD
compressed air is suPplied from only one iBlet
port, the spool
closes the outlet. If comprcssed air k Eupptied from botb
of
iDlet ports, then only the outlet port opens'
. AND logic is used il safety cirtuit "two hsnd operation of
p..ss" *here, the Pre3s opemtor has to eDgage both of his
iands to etart or operae the press, thereby; his hands srill
be protccl€d from accident (sB he don't have any third hand
ta be teft below tie Punch)
c

Truth Table :
a

Input Iaput Output

A B C (.)
Yes c

No No

No Yes Yes

No No No (b)

- (()
Fig.4.5.21

Note : Read seclion 5.8.2 for of lhis valve.

El,', 1!9 rE) 4-48 lntrod.to & Compon. o, Pn6u sys.

4.5.6.4 Ouick Exhaust Vatve:

w-201,
O. Explain wilh neat skotch Ouick Exhaust valve.
w-20r4
Q. Explain quick exhaust vatve.

This valve is specially used for pneumatic systems.

I)uring extetrsion or retraction of the cylinder, compress€d
air iB supplied to one end, and the air pr€seat in the other
side of tlle piston is erhausted to atmospheE.
Normally, it has to tske a long path to travel tltrowh pip€s
and tub€s, to get exhsusted through the erhaust po;t o1the
direction cotrtml valve.
To avoid this, quick exhaust valves are fitted to the cvlinder
ports.
Quick exhaust valve will exhaust t}te air to stmoEphere at
cyli-nder outlet port itself, and avoids the ne€d to havel a
long distance. Uaing quict exhaust valve will idcrease the
speed ofthe ptreumatic systems.

E
E

Fiz- 45,22(s) Fts.4.S,22(b)

Quick exhaust valve consists of a nrbb€r seal inside the valve
body.It has inlet port "P', cylinder port "A" and exhau.st port
'E".
When air is coming out fiom cylinder port -A", the rubbe,
seal closes the inlet port 'P", and opens the exhaust port "E"
as shown in Fig. 4.5.22(a).
When compressed air is supplied to inlet port "p" as shown
in Fig. 4.5.22(b), the rubb€r seal closes the exhaust port "E",
and allow air to llow to cylinder port.A".

Nole : Reler Section 5.16lor matic quick exhaust valve ci.cuit.

 4-49 lnlrod.to &

4.5.6.5 ,2 Poppet Type Olr€ctlon ControlValve :

. ,2 DCV is used to operate single acting cvlind€r

(SAC)'

. The 6gure shov{s 3i/2 spring rcturn t}'pe Poppet valve'

. lt has a spring-loaded poPPet and a st€m inside the valve
body.
When the push buttoa is
pressed, the ste6 Pushes the
poppet to open the PassaSe for
oil to flow from Port-P to
port-A. Otherwise, the Port-P
T
is closed.
In stam position as shown in
Fig. 4.5.23(a), there is (a)
connection from Port-A to
port-T. Oil under Preaaure
flows fmm single acting
cylinder to tank. Hence, the
SAC r€kocts. The inlet Port
port-P is closed.
I I
WheD the Push button is T

plessed, first, the st€m closes

the port-T. This Position is (b)
showtr in Fig. 4.5.23(b)
Further pressing the Pu3h
button, a-s showtr in
Fig. 4.5.23(c), causes the st€m
to push t}te poPpet against the
spring force. the PoPPet will
be lift.d ofr from its seat
T
making a passagB for the oil
under pressurc t flow fmm (c)
port-P to Port-A Thus, the
SAC exten&. Fig,4.5.2:i
 IFP (MSBTE) 4-50 lntrcd.to &
4,6 Actuators in Pneumatic System :

w-2012
O. What are acluators? How they ar6 classiied? Draw and label
a double acting hydrautic cylinder.

$2013
O. How hydraulic cylindels are classifiod.

s-2014
O. Give tho delailed classification ol pneumatic acluatorlr.

Actuators are those components of a p[eumatic system,

which produces mechaaical lrork output.

They develop forr:e and displacement, which is requircd to

perforE any sp€cific task.

the task may be of any kind, such as to move, to press, to

lift, to clahp and so on.

Speed of hydraulic actuato* depends on rate of flow of

compr$sd ai!.
Rate of flow of compressed ai! can b€ conholled usiDg flow
control valves.

Force developed by a cylinder is the product of pressure of

comprcssed air and the piston area.

We can control the force ol actuators by controlling the

pressure ofcompressed air using pressure control valves.

By controlling the direction of flow of fluid, by using direction

control valves, can control dircction of motion of actuatoF
IEP'." 4.sr lni,od ro & compon ot Pneu. svs
'ra"ra,
4.6.1 Classllicatlon ol Actuators :
. Actuators are broa(Uy classified itrto two groups, linear
actuators and iotary actuators. As the name tells, linear
actuators produce linear motion and rctary actuatoG
produce mtation. Detsiled classification is given in the
classifrcation chart.

ACTUATORS

+
B) Rotary ectuetors
A) Lineer actuetor€ 1. Limit d rotation
l. RotatiDg cylinder actuatora
(a) Varc type
2. Noa- rotating cylinder (b) PistDn typ€
(a)
(b) -
Single actiog cylilder
Double acting cylinder
i. Rack and
type
pinion

ii. Chsin aod sProcket

type
3. Special t,'pe cytinder8
2. ContiDuous rotation
(a) DiaphraSm cylinders actuator€
(a) Based otr dtectioD
(b) Tandem cylinder
i. Uni-directional
(c) Double rod eEd cylinder motor€
(d) Telescopic cylinder ii. Bi-dircctional
motors
(e) Cylinder wittrl cushionirg (b) Ba-sed on coDstructior
i. Geart]?e motor
ii. Vane t]?e motor
iii. Piston t}?e Eotor
Actuatorc are conuDon for both hydraulic systems and
pneumatic s,'stems. Only the difrerence is, hy&aulic
actuators ar€ made suf6ciently stmtrger to withstand in-side
oil prcssure aDd to develop hugE amount of force.
Whercas, the pneuDatic actuator€ are made Iightcr using
aluminum aod relatively thin cylinders as the inside
compiessed ail prressurc is just about 5 bar.
Eff,0" (rsar. 4-52 lnirod.to & Compon o, Pneu svs

4.6.2 Linear ActuatoB (CyInders) :

. Cylinders are linear actuators. They produce linear motion,
Ihey contain a piston inside the cylinder.
i.e. ,eciprocation.
When compressed air is supplied fiom one eDd of the
cylider, it exerts folce on the piston and hence the piston
moves to other end.
. There are two tlT€s of cylinders, namely, mtating cylinder
and non-rotating cytinders.

4.6.2.1 Rotatinq Cyllnders :

Rotating cylinderc are used to opemte work-holding devices

such as chucks, where the cylinder b€ing rotating, the piston
is ext€Dded or retract€d using direction contml valves.
The end coverc are fitted to cylinder otr ball bearings with
pmper seal. the end covers are fixed and the cylinder-piston
assembly rotates along with the spindle ol the machine.
The pistotr is connected to thejaws of the chuck by means of
leverc. Whe[ the piston ,etracts, the jaws move towards the
center to hold the wolk-piece. When the piston ext€nds, t}le
jaws move away llom the cetrter to rclesse the work-piece.

Pod A
Casing

Seal

Cylinder Eearing
Fis.4.6,r
Rotating cylinders sre used in chucls, collatcs, mandrels et
to hold ard release the work-piece while the spindle is
runoing.
lQl rrp tu SBTE) 4-53 lntrod.lo & Compon ol Pneu. Sys.

. There is no need to stop the machine for rcplacing the work-

piece. As soon as the job is fioished, just Siving support to
the running job (bv hand, wearhg gloves) and the lever of
direction contrcl valve i6 shifted. Thus the work_piece
released and removed.
. To mouat the Eev, work-piece, iust insert it ilr the chuck and
sbilt the Iev€r of DCv to other side.
. Operation is very easy; theie is no need to stop the machine'
no need of chuck kevs. The function of Ioading and unlmding
the job is very quick; it saves the machining tioe'

4.6.2.2 Non-rotatlng Cyllnders :

. These are simple t}?€ of cvliaders. The cvlinder G not

rohtiog; it is stationary.
. The piston €xtends or retracts deperdiflg upon the direction
of flow of Ouid. There are two t]?es of non-rctathg cvlinders'
siagle acting cylinder aDd doubte acting cylinder'
A) Single actlng qyllndor :
w-2013
o. Draw a ligure ol actual construction of single acting air cylinder
label
It is used to obtain lioear movemeot.
It has only one po!t, through which the compressed air
is admitted iDto it, to move the piston in one dircction'
Piston will retuE or co6e bacL due t
sPring force.
3/2 DCV i6 us€d to operate siogle acthg cylinders
(sAc).
spnns

ris.4.6.2
 ]FP (MSBTE 4-54 lntrod.lo E Compon, ot Pn6u sys

. It has two end covers, cap end cover 6nd rod end cover,
*hich covers the cylioder lioltl both ends and sre held
together by tie rods.
. O-ring is prcvided between end cover and cyliniler
interface so l! to ensure no leakage of the fluid.
. Cap end is having inlet port for the compressed air and
the md end is haviDA a vent hole.
. A sprins is pmvided at the rcd side ofthe cylinder for
,eturn stmke. The rod end is having a bush iDside
which the piBton rod slides. proper seals are pmvided
to prevent leakage of coDpressed air bet$,een cylinder
and piston.
B) Double acting cylndor i
. It obhin linear movemerlt.
is used to
. It has two ports, though which the compressed air is
admitted into iD either dircction, to move the piston in
both directions.
. That is, cohpressed air is supplied IioI! cap end port
for extension of piston atrd it is supplied from rod etrd
port for retraction of piston.
. 1/2 direction codtrol valves operat€ double acting
rylinders.
. In first position of spool ot 4t2 DCV, compressed air
flows to cap eod port of the cylinder and comes out
from the rod end port. Hence, the cylinder exteDds.
. In second position of spool of ,U2 DCV, compresseil air
flows t rod end port oI the cylioder alld comes out
Aom the cap end port. Hence, the cylinder rctrack.

Fis.4.63
ffi,rr (rs"r.) 4-55 lnlrod.to & Compon. of Pneu- Sys.

Cotritruction :

. It hs! two end covers, cap end cover and rod end cover,
which covers the cylinder Eom both en& and aie held
together by tie rcds.

. o-ring is provided b€tween end cover aod cylinder

interface so as to ensure no leakage ofthe fluid.

. Both end covers liave ports to admit the compressed air

in to the cylinder in either ilircction.
. The rod end cover has a bush inside which the pistoD
md slidB. Proper s€als arc provided to Ptevent
leakage of compreseed air between cylinder and piston.

Packing (iiction :

. In case ofcylinders, the piston is tightly insertcd in the

cylinder. Due tD rubber pistoo seals and tight fitting, it
requires some amount of force just to move the Piston.

. The minimum amount of force which is Equir€d to

move the piston in cylinder under no Iosd condition is
called packiag fictioo.
. Generally, packing fiiction is comidered to be same for
both extension and rctBctiotr. That fu, same amount of
folce is rcquiled to pull as well as to Push the piston in
the cylinder under no-losd.

. Net force lequircd = working load + packing frictiotr

@1",." (MSBIE) 4-56 lnlrod.to & Compon. o, Pneu svs.

4.6.2.3 Other Types ol Cytinders

w-4)13
o Sk€tch and labellino diagram of pneumatic diaphragm
cylind6r-

A) Diephragm cylinder :
. lhese are used for very small displa.cmeDts. There
will be a diaphragm imtead of piston inside the
rytinder.
. The diaphra&D deflects when compreesed air is
admitted into the cylinder. The diaphraSm is fitted
with a piston md ard hence the piston md ext€nd! or
letracta,

Fig.4.6.4
B) Double rod end cyliDder:
. These cylinders have piston rod on both sides of the
piston as shown in the Fig. 4.6.b.
. By this arrangement, work is carried out on one side
atrd the other side is used to operate linit switch and
limit valves.

l'is..1.6.5
ffi,r" tu."t E) 4-57 lntrod-lo & Compon ol Pneu. Sys.

C) Tardem cylinder :

w-m13
O. Whsl is randem cyllnder? E&laln wlth neat skotch. Draw
symbol of it.

Herc, the cylinder is divided into two o! more

compartments. There witl be pistoE in each
compartment.
AII pistons arc fitted to a siagle Piston rod aB shown in
Fig. 4.6.6. Tandem cylinders are used to produce more
amount of forre,

Fig.4.6.6
D) Cylinders sith culhioninS:
If the cylirder is tong, tiat is, if stmke len8th is morc
and the speed is high, then naturally, the pi6ton-
impact on end-covers is couiderably high.
CoDtinuow haEmering of piston on these cover_Plates
causes loosening of tie rods and leakage of fluid. Also it
will damagE the cover plates. Hence to avoid sudden
inpact of pistod otr the cover plstes, cylinders with
cushioning sre us€d.
A cylinder with cushioDing is shown in Fig. 4.6.7. It
has intcgxal Ilow control valve aod check valve in its
end eover plates. The pistoa rod has a projecled nose
equal to the dia$eter of inlet port pa$ag€.
(i) During r?traction :
. When the piston is mo\ring towards left, once the
piston nose entcrs the port, the paEsage closes.
Only the restricted passage thmugh the FCV is
left, ald heace the flow reduces r$ulting in
further movement ofpi-ston slower.
. T'his is how the cushioning (slow end of stmke) i,
achieved.
12rp 4-58 lntrod.to &

O-nng

F19.4.6.7
(ii) During extensiotr :
. During extensioD, when the pistDn is moviDg
towads right, compressed air is supplied to
"port- A".
. Now, since this port is closed by the nose,
compressed air hss to llow through the restrictcd
passaSe of FCV. It will Dot Foduce su6cient
force to start moveEeat ofthe pist n.
. Hetrce check valve is pmvided through rrhich,
compressed air llows freely, and move the piston.
E) Telescopic cylindor :

9m11,2012, W-m1r,2013
o. Oraw and explain lhe of telescopic rylinder.

Telescopic cylinders are used ir cranes ard hoists to

lift the heavy objects to great€r height.
A t€lescopic cylinder coDsists oftwo or more Dumber of
cylinders, one inside the other, which extends one by
one sequentially whetr coEpressed air ie supplied
under preasure.
Hence, a compact teleacopic cylinder v.ill extetrd to
greate! length. Fig. 4.6.8 shows a telescopic cylinder.
ffi,r" (rs"t.) 4-59 lntrod.lo & Compon. ol Pneu Sys.

Flg,4J.E
f') Cylindere rith sGDsors :

. For automatic continuous and sequential operation of

cylinders, it iB Deeded to sense the displacemeEt and
position of pistoa of oae cylinder and the signal output
is given as input to the ot}ler.
. Sensore are u,sed for this purpose. I'her€ are several
tlTes ofsensing devices; some of them are given below.

Limit valveE : I'hey open when the cam operat€s the

loller and supplies compressed air to
the pilot operatDd valves.

Limit switches : Makes electric supply'on" when cam

operat€s the rcller aDd supply curretrt to
soleaoid op€rated valves.

Optical s€nsors : These ar€ photo-electric sensors which

s€trEe the light rays and produce electric
sigDal, which is amplifred and givea as
input sigDal for soleDoid valves.

Electronic Bensors : Thes€ sensorE s€nse the magnetic 6eld

of a permanent magDet fitted to the
pi6ton, and produce electric sigDal,
which is amplified arrd given as input
signal for solenoid valves.
ffi,." 1,;ssrey 4-60 lnlrod.to & Compon. of PneLr. Sys

4.6.3 Botary Actuators :

91rr1
O. Stato the difigrorn typ€s of air moloc. Explain any one.
w-alt
O, Explain with noat sketci 6ny one typ€ of air motor.
w-xr11
ii Give the classificalion ol air motors and explain any ono ol it.

4.6.3.1 LimitedRolationActuators:
These mot rs arc bi-directioDa.l motors. They can run in both
dftectiom, but for a limited number of rotatiotrs.
A) Vano typo :
. Fig. 4.6.9 shows v6ne type limit€d rotatiol motor.
. It has a cytiDdrical block with a pairs of finely ground
flat vanes iD its radial slot.

FIs.4.6.9

When compressed air is supplied tlEough port-d it

exerts pressure on tlle vanes and heDce, the motor
shaft rctate in count$ clock-wise dircction.
When compressed air is supplied thmugh port-B, the
motor shafi mtat€s in clock-wise direction.
Id,t" 4-61 lntrcd.to & Com

B) Plston typ3 (R.ck and Pinlon tyPo) :

. Fig. 4.6.10 shows vane t]'pe limited rotation motor'
. It has a cylitrder inside which, two pbtons a'e
mounted.
. Conoection ftom port_A is takea fiom either end of the
cylinder as shown i-n 68ure.
. Connectioa to Port_B is takeD at the middle of the
cylinder.

il

-a
t
Fig.46.10
when compre$ed air is supplied through port-A, it
exerts prcssur€ on the pistoDs from either e[ds oI tho
cylinder-
The pistors move towards each other. Compressed air
flows out through port-B at tie middle of the cylinder.
The pistonE ar€ frtted with rack 6nd Pinion
arrangement. Hence the pinion rotates in counter
clockv,rise drrectioD.
When compressed air is supplied through port-B' it
exerts presure on the pistoos from inside out of the
clinder.
the pfutons move away from each other. Compr$sed
air flows out tbrough port-A, hence the pinion rctat€s
in clockwise direction.
 IFP (MSB 4-62 lnrrod.to &

4.6.3.2 Continuous rotation Actuators (Botary Motors):

. These motors can run coDtinuously.
. All rotary compressors are motorB! if compressed air is
supplied t the port of a ,ota.rJ. compressor, then its shaft
rotstes.
. Rotary motors are bi-directional. If inlet and outlet
connections are int€rchanged, they can run in opposite
direction.
(A) Gear typo alr molor :
gn)r2
o. motor with noat skgtch.

Fig. 4.6.11 shows an ertemal gear motor.

It corrsists of two spui or helical gears, which are
meshed with each other, and are mounted inside the
casing.

1t

t
Hg.4.6.rr

When compressed air is supplied to the inlet, it exerts

force on the gear t€eth, due t which gears rotate, sha_ft
rotates and compr€ssed air comes out from the outlet
ffi IFP (MSBTE) 4-63 lnirod lo & Compon. ol Pneu. SYs

(B) Ggnsraled rotor (Ge rotor) motor :

. ltris motor consists of two generated rotors as shown

in the Fig. 4.6.12. One is havirg exterdal tceth and
other is having htemal teeth.
. TlIe rctor with extemal teeth rctates inside the rotor
havhg interoal tpeth. The inner rotor tu haYina one
tooth less tha.n that of outer rotor.

Casing -

,,2

+
O!tlel
€

Fig.l.6.12

When compressed air is supplied t the inlet, it exerts

force otr the gear teeth, due to rvhich gears rotat€, shaft
rotat$ add co6pressed air comes out from the outlet.

(C) Vane Type Ai, Motor :

w-an2
O. Wil'h a neat sketch, gxplain construction and working of vane
type air motor.

Itconsists of a cylindrical rotor, which is mounted with

an offset inside a cirtulat casing.
The vanes ar€ seated in the radial slots of the rotor and
held against the casitrg by spring force or centrifi4al
force.
Hence therc l,ill Dot be any leakage of compressed air
betse€n the vane tips aDd the casing.
ffi,ttt, SBTE) 4-64 lntrod.to & Compon. ol Pneu. Sys

hrer + $ o,uet

Fig.4.6.ll
When compr€ssed air is supplied to the hlet, it exerts
force on the vanes, due to which cyliDdrical rotor
mtates, shaft rotates and compressed air comes out
from the outlet
(D) Axial piston type 6ir motor

Cylindor

maD Swash plate

€
O!l

+IN wza-,
Fig.4.6.14

- is shown
Straight ar.is piston motor i-n figure 4.6. 14.
In straight axis pist n Dotor, the cylinder blocL is
fitted to tle drive shaft, i.e. the ards of mtation of
rctation cylinder block aod the tlrive shaft are same.
 4-65 lntrod.lo &

. t.tle shoe Plat€ is mounted oD a s\ra.sh plate' which is

6xed at aD augle to the sxis of rctation.
. I'he angle of swoBh plate can be Yaried to chaDge the
speed olthe motor.
. When compresaed air is supplied to tie inlet, it ererk
force oD the pistoDs, due to which cylinder block
rotatas, shaft rotates and coDPressd 6ir coDea out
from the outlet.
(E) Rtdlrl Pllton Air [otor:
w-m11
Q, D€w a noat sketch and oxplain woiking radial piston type
molor.

Crank

Connecling rod

Cylinder bloc*

Fl& 4.6.15

Fig. 4.6.15 shows a stationary cylbder t)'pe radial

pistotr motor.
It coNists of a stationary cylinder block, in which' five
cylinde$ are araDged coPlanar with equal angle
between them.
Totally tiere are five pistons, one rcciprocating inside
each cylinder. All pistoru are connected to a single
crank by individual connecting rods as shown in
Fis.4.6.15.
u" IFP (MSBTE) 4-66 lntrod.lo & Compon. ol Pneu svs.

All suction valves are connected to a single suctiotr pipe

and all delivery valves are coD-Dected to a single
delivery pipe.
When compressed air is supplied to tbe inlet, it exerts
force on the pistons, due t which cylinder block
rotates, sha-ft rotates and compr€ssd air comes out
Iiom the outlet.

4.7 Pip€ Materials lor Pneumatic syslems :

s-21t13
Q. Enlist various matodals used lor hydrautic pipes.
Q" How hydraulic pipes are cl.rssiriod?
O. What are th6 various types of hoses us€d in pneumatic
syslem?
w-m13
O. What are th€ types ol pip€s used in pneumatjc syst6m?

A) pipes: o Cast imd.

Rigid
o Low caibon 6t€els,
o A.lloy stcels,
o St{inless steel,
o Copper aod its alloJrs,
o AluminuD end it6 alloys.
B) Flexible hoses o Ylon braided hoses,
o St€el yire rcinfored rubber hos€s,
o Poly-ur€theDe tub€s, Nylon tubes,
o Polyethyleoe tubes, PVC tubes,
o PobEopylene et _

C) According to streDgtl o Staldard pipe (STD)

o Erha strong pipe (XS)
o Double Ertra stmug pipe OO(s)
[Fl,r",us"le, 4-67 htrod.lo & compon. ol Pneu' svs'

4.7.1 Flexible Hose:

w-m|l
O. which mate als aro usod for laygrs of hos€s in pn6umatic
systom. Oraw cross gection ol pneumatic hoso pipe'
w- 13

O. Draw conslruclional details ol pneumatic hose Why hose is

required in Pneumatlc circlils.

EA E6
96 .!P

9d
ti&9 €:

3
F"lg.4.7.r

Flexible hos€ pipes are extensively emPloyed itr pneuDatic

syst€ms and pneumatic systems as tiey are eaay to
acco modate and to connect \rith in the available space
I'lrcse pipes are made of elashc matenal and can be bent
easily.
f'lexible pipe is made of several layers with hetal wile
haiding betweeD ttrem. Thos metal wire r€inforceEent
incresses the strengtl of the pipe.
Sr a-ay€r Function Materisl
No.
1 Tube Conveys the Polyethylene
hy&aulic
compressed air
2. tr.ir3t Pmt€cls and Metal wirc (st€el
r€inforceneDt strength€ns the or copper)
tube
EFl,rr,r""-. 4-68 lntrod.lo & Compon. of Pneu. sys.

Sr. Layer Ft ction Material

No.
3. Adhesive layer Holds the Rubber
reiaforceDeat
layers, prot€cts
against YibBtioas.
4. Secoad Prot€ck the 6rst
r€inforcement !einfoteDeat (cottoD, nyloD,
polyest€r
synthetic fiber

5. Protects 6:om Polyethylene

abresions, dust,
vibrations,
sunrays..
Adv.Itagea ol flsxlblo pipss :
r Flexible pipes can easily bent ard accoDmodated iD the
available space
. It makes the system simple and compact.
. It carl be fitt€d to moving components, a rigid pipe can't.
. lt has hiCh streDgth and less weight.
. It has Sood resistsnce to cormsioD, fire, moi-sture, abrasion
and penehation.
. It absorbs vibration and noise.
. It c@peDsates fol thermal expaneion and coatraction.
. Alignment is easy and accurate.
. Suitable for wide ratrge oftemperuture.
Dlladvantagsr ot llexlblq plpes :
. Cost is hiah.
. Need pmper support.
. Other compooents cannot be mount€d tsLing its support.
. Use of morre number of flexible pipes makes the system
clumsy and afrects the aesthetic view ofthe system.
 MS 469 lntrod.lo &

4.7.2 Selection ol Pipelines lor Pneumatic System

w-2011
o. List tho factors to be consire.€d tor s€l€cling the
pi,es while
dosEnl.lg lfi6 Pnsurnalh sFtom.

. pla[t is situatrd suitably away

GeDerally, the air compressor
from the main worL ststioa. I'he reason is that of noise'
vibration and related Pmbleme.
. Compr€ss€d air is stored in the air receive' ttDk, frorD
*'hich
it is talen to main work stahon.
. While laying the pipeline, we should take much care to 6ee
that th. pro"trre drop r€Eaias a.s low as possible Oess than
0.1 bar).
. I'he fo[owing are some importsirt fsctoE to be conBidered
!.bile s€lecting pipeli& for Pneumatic s,'stema :
1. Pressure drop in PiPes
2. Prcssure of comPressed air
3. Rat,€offlow ofair
4. PerDissibte Prcssule drop
5. Material oftube and fittin88
6. Plcssur€ mting ofPipe
7. Izngth & diameter ofPiPe
8. WorkitrS enviroDmeat, etc

4.7.3 Prassure Rltlng3lor Plpe or Tube :

. Preseure ratiag is erPress€d with two terms; bust Pr€$ure
and opeiatlng Pr$sure.
. Bursipreeaure iB the marimum ptessur€, which the tube can
witl-staDd. Pip€ may buBt iI pr€s6ur€ is more thaD this'
. Operating prc$ure is the msximum prEssure at rehich the
tube is to te operated, considering facto! of safety'
. Factor of saftE i6 tlre ratio of burst pressue to operating
pr€sBure.
. Pr€ssure rating depenals oD many factors such as
1. Outtr diameter oftub€
2. ltickness oftube
3. Intemal diameter oftube
4. Material oftube
5. Maximum allowable stress
6. Opemting temperatu.e et .
 @rrn Juserey 4-70 lnlrod.to 8 Com ol PneLr. Sys

4.7.4 Requirements ol Fluid power plumbing :

s-2012
O. What are ths requirem€nts ol good clmopressod air powsr
ptumbing?

92t rt
O. How good piping system is dssigned. Stats th€k tipo.

w_2ar13
O. W.ile any tour tips lor good piping in pneumalic systems.

Following points sre to be coNidercd while designing a

hydraulic piping syst€m.
1. Ihe conducto (pipe) must be ofsuftcient strEtrgth to coatain
compressed air at desired working preseure, to rBist
the
highest posaible shock preasure, aDd to support the devices
that are mourted on it.
2. The _t€rmitral points (unions, flang€s etc.) must be pmyided
at all junctions to achieve ea.sy rcmoval or dismantling or
maiDteDance.
3. Port seals should b€ deBigaed to recluce coEpr€ssed air
losses.
4. The conductors must have smooth htcrnal surfaces to
reduce loss ofpower due to friction.
5. Corect size should be used which causes best llop
cotrditions.
6. Use of elbows, beads, ,eversals etc should be as less a.s
possible.
7. Use of manifolds ,educes the need of joints and lengthy
pip€s, thus it imFoves the systeh,s efficieocy
8. Tte lines must be kept cleaa and Ilushed rcgularly.
4.7.5 Requlrsment ol Hoses and Hoae Finlngs :

1. Hoses should be flexible sufficiently.

2. Hoses should b€ able to work with maximum syst€m

3 Hoses should be govided with proper end fitting.

4 Hoses should be compressed air r€sistart.
 E)

5. The inner tube should be compress€d air resistant seaDless

tube of rubber.
6 The i[[e, tube should be braided with wir€s of myon, t€xtile
or steel for rcinforeemetrt.
7. The oute! cover should b€ comprcssed air and weather
re8istsnt.
8 Wbile assembling, care should be tsken to avoid sharp
b€trds, twist and telsiotr in the hose.
9 Care should be taken while instrllatioD r€gardilg tbe
permieaible timits of t€mperature, which the ho8e c'n
withstand.
4.7.6 PiPe Size Specilication :
92012
O. Explai (1) Standard pip€ (2) Extra strong pipe

GeneElly, pipe size i.s speciied in t'he following tiree waya :

1. Noninal pipe rize (NPS) : ThiB aumbet indicatrs the baae
diamet2r of pipe in incbes.
Exaltrple: )t inch, % inch, 1 iDch, 1t4 inch et''
Schedule (SCE)I This Dumbr is based on wall thicknees'
pipe'
Grcat€r tlre SCH, geat€t wil be the wall tiickDess of
A schedule numbet indicateB tle apPmximat€ value of

scH =
__s_
1000 x P

Where P = s€wice Pressure aDd

S = allowable etress
EraEplq SCH number 5, 10, 20, 30, 40' 50' 80' et'
Schedule ,(), tO sDd 160 are widely uscd-
1- Pipes ar€ stso ctassified as StaDdard (Sm)' ext'a
strong (x5) size, double ertra stmDg 0O(S) based on
strcngth.
(i) STD is neartv equivaleot to SCH 40'
(ii) XS is nearty equivalent to SCH 80'
(iii) )O(S is nesrly equivaleat to SCH 160.
-i',t, tr""r.t 4-72 lntrcd.to & sys.

For any NPS number, OD (outer diarDet€r) is fixed.

With inclease in SCI{ nuaber, ID .educes a_nil thickness

Example

For NPS of I inch, outer diameter is fired, equal to 1.916

But, inside diamet€r is 1.049 for SCH4O, O.gbZ for SCH8O

and 0.815 fo! SCH160.

Hence pipe wall thickness is 0.133 for SCH40.0.tZ9 for

SCH80 and 0.25 for SCH16O.

Table showing pipe size specfications :

NPS Tvpe scH OD inch ID inoh Thickness inch

STD 40 1.315 1.049 0.133

I inch 80 1.3 r5 0.957 0.179

)o$ 160 1.315 0.815 o.25

2 inch STD 40 2.067 0.154

XS 80 r.939 0.218

)C(S 160 2.375 1.689 0 343

STD 40 3.5 3.066 0.216

3 inch xs 80 3.5 0.3

)o(s 160 3.5 2.626 0.437

 SBTE) 4-73 lnlrod.lo & Co

4.7.7 Pipe Fittlngs and Tube Flttlngs:

w-nn2
O. Name any eight pipe and tube litings. Write iheir lunction in
briel
Pipe fittings are the connectoE requircd for connecting the
pipes and tub€s. TheIe are variious Linds of pipe fittings
dependiag on the applications.
ltrcre is very small amount of Pressure loss in any pipe
fitting, but vrhen many numbels oI fittbgs are there in anj
circuit, the cumulative effect of thes€ losses is coftiderably
large
Sr. lype of Applicatiotr
No. Fitting
1 Male lhis fitting is used to connect pip€/tube to
thrcaded hole ofthe manifold.

2 Female Itis fitting i6 used to coDnect pipeltube tD

nipple with exttrnal thread.

3 Tee This fitting is u6ed to coDnect three Pipes.

4. Cross This fitti.trg is used to connect four pipes

5 Elbo* T'his fittiag i! used to have sharp right

angle tum ia the pipeline.

6 45 degree This fitting is used to have sharP 45

elbow degrce tum io the pipeline.

7 Bend This fitting is used to have long radius

curved right angle tum in th€ pipeline

8 Reducer This fitting i6 u6€d to connect two pipes of

different diaseters.

9_ Double nipple lhis flttidgis used to coDnect two pipes

hsYing internal threads.

10. Plug 'Ihis frttiDg is used to close the porLs.

@,re 1,,,sere1 lnlrod.to & Compon. ot Pneu. Sys.

4.8 Seals in Pneumatic S stem :

The maio function of seal is to avoid lealage of presaurized

fluid. Izakage may b€ of two t,?es, int€mal leakage and
external leakage.
Er.temal leakage can be easily traced out, it i-s seetr from
outside. External leakage results in wa.stage of F€ssuiized
fluid. In pneumatic systems, ext€rnal leakage causes
slippery floo!, dirty surroundilgs, accidents and fire hazard.s.
lnternal leakage is difficult to detect, it happeDs iDside the
srstem, it can't be seen ftom outside. Irtemal leakage
results in reduces efficiency, power loss and reduced load
carrying capacity.

4.8.1 Functions ot Seals

s-2012
O, What are the vaious ,unctions ol seals? Write the types oi
seals used.
w-mt3
Q. Write any {our lunctions of hydraulic seals.
*2014
O. Give th6 functions ol hyd.aulic seals.

. Maitr fuDctiotr ofseal is to stop lea.kage offluid, to stop loss of

complessed air to the surroundings, to retain the compreased
air within the system.
Other frrnctions are :

. To keep dust, dirt and contamirants away from the [uid, to

avoid them entcring into the compressed air ftom outside.
. To avoid power loss, and to improve ef6ciency ofthe system.
. To k€€p the suirouddingE cleaa (in case of preumatic
syst€Es).
. To svoid slippery floor,dirty surroutrditrgs, accidents a-nd fiIe
hazails (in case of pneumatic 6ysteDs).
EEl,." 1u."t.1 4-75 lnrlod.io & Compon. ol Pneu. Sys.

4.8.2 Classilication of Seals :

s-2013
O. Skolch the cup seal, and write jts applicalions.
s2014
o. Ditlerentiate b6tuvo6n static s6al and ic seal

A) According to lhe melhod ot aeallng

. Positive seel : perfect sealing, 10G% lee.k-proof. Not
even a minut€ dmp of compressed air can pass thmugh
it.
. Non.positive seel : allows a small amount of leskage.
This lealage of conpressed air serves the pu4nee of
lubricating the spool irside the valve.
B) Accordlng lo lh€ appllcatlon :

. Ststic aeal : used between mating parts haviDg no

relative movemeEt,
Example : Sealing between Flaoges, gasket etc.
. DfrnsEic aeal : used b€tween matitrg parts with
relative tootion.
ExaDple : liDear Eotion seal between rod eDd cover
and piEton rcd, ,otaiy ootion 6eal betwe€n compr€ssor
shaft and cs8ing, et .
C) According to the shap€ conrlguretion :

. O-ri.g, quad-rinc, T-ring, V-ring, U-cap, Hat ring et .

I
B
i
I
L

I {up scrl Pbtor T-s..| Rod f{.al

Fis.4.t.l
E IFP (MSBTE) 4 76 lnlrod.to & Compon. ol Pneu. Sys.

Materials used for seals :

Poly-tetra-Fluoro-Ethylene (PIFE) and Poly-Uretlune(PU)

ensure maximum durability aod performance v{ith minimuD
maintenance. Othe! materiab commonly uBd are rubber,
leather, Fibe, Teflon, plastic etc.
U-cup seals arc used for
l. Pistons and pistnn rods ofcylinders
2. Pistons and rods ofaccumulators
3. Pistons of comprcssor€
4.8.3 Causea lor Fallure ot Seala :

w-tu11
O. State any tour rgasohs of tailure ol pneumalic seals.

Following are the reasons for failure of hy&aulic seals.

. Excessive heat . Excessive load
. Excessive clearance . Excessive pmssure
. Impmper fitting . Improper groove geometry
. Impmp€r filt€r rating . CoDtamination offluid
. Idle stomge of8eal fue hardedng
. Abrasion

'1.8.4 Various Losses ln Plpea :

1 Major loss of head due to friction in pipes, can be calculatcd

by using different formulae, or ushg NomoSram.
2 Minor losses are due to pipe frttings (such as bends, elbow,
valves et ), the vatves a.ud 6ttin$ are giyen by t}te
manufacturer, and are "expre$ed id the equivalent lengtis
of straight pipe of the same diameter'.
3 Head loss due to lealagp.
4 Head loss due to broken seals.
5 Head loss due ta wastage of air.
ffi,rr (rsut=) 4-77 hlrod.to & Compon. ol Pnou. SYs

4.9 Fllter in Pneum m

s.ml2
O. What is lilter : What is its tunc{on? List the types of tilters.
w-2012
O. what is function ot tilled How lilters are classified? Name any
four advanlages o, bypass fiher.
w-24r13

O. Give lhe classilication of filters used in pneumatic syslem

Explain any one of them.

Func'tion of sir filter is to reEove dust and moistu.rc froE

compressed air, arld to provide cleao compressed air to the
pneuEratic s),stem.
Dust in compressed air increases frictiotr b€tweea the
moving parLs; hence there witl be wear atrd tear ofpsrts aod
loss of etrerBr in the form of heat.
Dust aDd Eoisture combitres with lubricant oil to form very
hs.rd to remove varxrsh (gel) and choke up the ports and veitrs
in the system. It crcates distuibance to llow.
Hence the dust has to be reEoved fiIst and clead working
compressod air should b€ supplied t the syst€m.

4.9.1 Classilication Filters :

A) Classflcatlon accordlng to luncllon
1) Surface tlT€
2) EdgB typ€
3) Depth t}?€
B) Classlllcdion .ccordlng lo conatructlon
1) By-pass type 6lter
2) Full flow filter
3) Proportional flow filt€r
4) Indicator tlTe filter
[Pf,.r 1rsur.1 4'78 lnlrod.to & Compon. ol Pneu. Sys.

4.9.2 Surlace Type Fllter :

This is also called screen

filt€r. In surface tJTe 6lter,
the soUd impurities are
scrcened and retained on the
surface offilter.
Filter elements are meshes of
metal wires, woven cloth oI
metal wires o, yain etc.
Wirc meshes of different sizes
are used. These filt€Is can be
cleaned and reused.
Fig.4.9.l

4.9.3 Edge Type Filler :

r In this tlTe of filt€r, the solid hhr

impurities are hapf'ed at edges
of the platcs which are
aEanged parallel to each other =
with negligible clearness =

Different t ?es are disk type,

ribbon tpe, platcd tlTe. These
6lt€rs can be cleaned and
reused. Fig.4.9.2

Dbk tme filter is rat d at 98% rehoval of paiticles liorD ,()

to 125p, Ribbotr typ€ from 25 t 500p.
lq^l rFP TMSBTE) 4-79 lntrod ro & Compon. ol Pneu. Svs

4.9.4 Depth Type Filler :

In depth tlTe filte$, the solid impurilies enter into the filter
element to certain depth and happed there.
The filtcr element are made of
oaterials such as sintercd
matcrials lowders, sbtcred I
ceramic Powders, tratural aDd
synthetic fibers, ysm, cottotr
etc.
t
Filter element of shtaed
powders can b€ cleaoed to
extcot by back washidg. But
other twes, vrhich are
mentioned alove, cannot be Fig.4.9.3
Eus€d.

4.9.5 By- Pass TyPe Filter :

It has a spring-loaded by-pa.&s

valve in
between inlet atrd
outlet port.
Whelever the 6lter elehetrt ig
chocLed up to a greater
extent, this valve openE to
make dircct coatrectiods ftom
inlet t outlet.
thus it the filt€r
safeguard.s
element agaiDst any damage
due to high-pressure Fig. {.9..1
difference.
EEl t" ru""r.r 4-a0 lntrod-lo & Compon. ol Pneu. Sys.

4.9,6 Full Flow Filter r

As the name implies, the frrll

flow of oil uEder prBsune is
filt€r€d.
the oil under pressure has to
flow thmugh the filt€r
elebent complet€ly, and the
enthe oil is fiItercd and clean
oil is coming out of the filter.

l'ig. {.9.5

4.9.7 ProporlionalFiller:
In Foportional 6lt€r, a
portioa of the oil under
Pressure o y Passes through
fiIte! element.
R€st oftbe voluEe of oil under
pFessure pass€s dircctly
uD.Eltcred thmugh the
venturi.
This is needed ifthe discharge
thmugh filt€r element iB less,
that is, the filter element is
very 6De, and the system treed
more diBcharge. Fig.4.9.6
Ef,rp (r""te) 4-81 lnlrcd.to & Compon. ol Pneu. Sys

4.10 lmportanl Examination Questions and

Answers
Please refer e-book for complete solution
Note :

1 Ptease dawnloo.d our free e-b@h for detailed ansuers

of follawina q uestions.
2 Nl Quzstion-s & Answers cowr thz comPLetp chapter.

{.1 Intloduotlon
Q. 1 Dmw general layout of pneumahc s,'stem aBd Iab€l
the components. ($ff,W-fl, W'13' S-f4)
[Section 4.1.1]

Q. 2 Name the components olpneumatic system. What arc

the factorc to be considered while selectiflg them?
tsections 4.1.2 and.4.1.31 (W-12)

OR

Q. 2 LiEt out main elements ofpneumatic syst€m

tsection 4.1.21 (W'13)

Q.3 What are the merits of pneumatic systtms?

[Sectian 4.1.4] (W-12, W'13' 9r4' W-14)

Q. 4 What are the limitations ofpneumatic systeh?

[sectian 1.1.5] ($12' 9r4 w-r4)

4-l Alr R€aGiv.r

Q. 1 What is the tunction of aii receiver? Explain and dravr
its symbol. (S-12)
@l r" 1u""r.y 4-82 lnlrod.to & Compon. ol Pnau. Sys.

4A FRLUntt:
Q. 1 What is FRL unit? Explain its fi,nction. (gt2)
OR

Q. 1 Whst is mean by FRL unit in pneumatic circuits aad

state the tunction ofeach. ($13, W.19. W-14)

Q. 2 Dra," and lab€l a;r e$iato. [Section 4.3.2] (W-12)

OR

Q.2 Explain with neat sketch the construction of non

relieving prcssule regulator. [Section 4.3.2] ($fg)
Q. 3 How fine spray or atomized Bplay of lubricating oil is
ot'tahed iD lubricator of F RL unit.
tSection4.3.8l (W.11,$12)
OR

Q. 3 Dmw lab€led sketch ofair lubricator. (W.12)

ISection 4.3.3]

a.a Cond.Dlatl@ ol Wst t

Q. 1 Stats the functions ofmoisture sepsrato..
lsection 4.4.1] (913)
OR

Q. 1 Enlist the pmblems ercourtered due to moisture

coDdeDsatioo in pDeumstic system. Name ttre
different t)?es of air drye$ to avoid moisture
coDdensatiotr. IseclioN 4.4.1 and 4.4,31 (S-14)
ffi,r" tr"ut.t 4,83 lnrrod.io & Compon. ol Pneu. Sys.

4.6 Control valeo!

Q. 1 State diferert twes (ary 4) ofpressurc control valves
with their applicatiotrs. [Section 4.5.3] ($11)

Q. 2 what is the tunctiotr ofpressure reliefvalve? Where it

is located? Sket{h dircct operating prcssure rclief
valve. [Sectian 4.5.3.1] (W.r2)

OR

Q. 2 With a neat sket h, explain the tunctioning of simPle

pressurercIiefvalve.[Section4.5.3.1] (S.14)

OR

Q.2 Explain pressure rclief valve used in pneumatic

syatalr,n. [Section 4.5.3.1] (W-r4)

Q. 3 Explain with neat sketch working ofdirectly operated

pressure reducing valve. [Section 4.5.3.2] (Sll, W.l l)

OR

Q. 3 Explain the workiDg of pressure rcgulator with neat

sketch. [Section 4.5.3.2i (W.14)

Q. 4 Explaia worhing of directly operated check valve with

rcaL skelcb. [Section 4,5.4.1] (S-tz)

OR

Q. 4 State the tunctiotr ofcheek valve in ptreumatic ci&uit.

Isection 4.5.4.11 (W.rs)

Q.5 ExplaiD the working of mtary spool type valve Eith

le l skekh. [Sectiatl 4.5.4.2] (9f 3)

Q- 6 Draw a neat sketch of 312 D.C. valve. Explain its

wolkt^g. [Sectian 4.5.4.3] ($12, W.l3)
l&1,r" rus"rEr 4-84 lnlrod.to & Compon. ol Pn6u. Sys.

OR

Q.6 Sket{h the two positions of sliding spoot t}?e 3/2 DCV
and explain in briel lsection 4.5.4.31 (S-14)

Q.7 Draw a sketch of normal and actuated positions of 4/2

DCY. [Section 4.5.1.4] (S-11)

OR

Q,? Sketch the two positions of rotary spool type ,U2 DCV
aad explain in brief.Ise.tion 1.5.4.11 (S-14)

Q,8 Explain 4 way 3 position direction contml valve used

in pneumatic syst€m with sketch.
tsection 1.5.4.s1 (S-11)

Q.e Explain why 412 DC! is pr€fered for pneumatic

syst€ms and 5/2 DCV pneumatic system.

lsection 1.s.4.61 (S-14)

OR

Q.e Explain the working of push button operat€d 5/2 with

neat sketch D.C. valve used in pneumatics, with neat
sketch and its s].rnbol. lsection 4.5.4.61 (W-ld)

Q. 10 What is flow control valre? [Section 1.5.5] (S-11)

Q. 11 Explain noa pressure compensated flow control valve.

lsectiDn 4.5.5.21 (S-11)

Q. 12 Explain non-rctum tW€ flow coDtrol valve used in

pneumaticsystem.Isectirn4.S.S.SI (W-14)

Q. 13 Explain with neat sketch the working of time delay

.val'I,e. [Section 4.5.6.1, (W-11)

Q. 14 Explain shuttle valve with neat sket h.

tsectiarL 4.5.6.21 (W-r4)
Eff,r" (rs"t.) 4-85 lntrod.lo & Compon. of Pneu. Sys

Q. 15 Explain with neat sket{h quick Exhaust valve.

[Section 4.5.6.4] (W_11, W_14)

4.6 ActErt rs ln lhou.Eatlc Syatetn:

Q.r What are actuators? How they are classified? Draw

and label a double acting hydraulic cylioder. (w.12)

OR

Q. 1 How hydraulic cylinders are classified. ($fg)

OR

Q. 1 Give the detailed classification o{ pneumatic

actuators. (9f4)

Q.2 Draw a figure oI actual construction of Bingle acting

air cylinder and lab€l iL.lSectinn 4.6.2.2(Nl (W-13)

Q.3 Sketrh and label iine diagram of pneumatic

diaphragncylinder.lsection4.6.2.3(Al (W'13)

Q. ,r What is tandem cylinder? txplair with neat skekh.

Draw symbol of it. ISectian 4.6.2.3(0l fW-13)

Q.6 Draw and explain the working ot telescopic cylinder.

tsecti.on 4.6.2.3(E)l (911, 912, W-11, W.13)

Q.6 Stat€ the different types of air xoot Is- Explain any
ore. [Sectinn 4.6.3] (S-11, W.11, w.14)

Q.7 Exptain g€ar motor with reat sketch. (S.12)

tSection 4.6.3.2(Dl

Q.8 With a neat sketch, explain coNtructiotr and working

ofvaDe t):pe aii motor. [Section 4.6.3.2(0] (W.f2)

Q.s Draw a neat sketch and explain lrorking radial piston

typehydnulicmotor.lSection4.6.3.2(E)l (W.11)
l4El trp MSBTE

4.7 Ptp. Uetorta,ls lor Pnouertlo sr.t6l[3

Q. 1 How hydraulic pipes are classified? (9lS)

OR

Q. 1 lvhat are the various tlpes ofhoses used in

pneumatic s,.stem? (S-f3, W-13)

Q.2 Which matsrials are used for layers of hoses in

pneumatic system. Draw cross s |ction of pneumatic
hoae piw.lsection 4.7.71 09.1r, S-13)
OR

Q.2 Drai, constnrctional details of pneumatic hose. Why

hose is required in pneumatic ctucuits. (W.fg)
tsectian 4.7.11

Q.3 List th€ factors to be coNidered lor selectiDg t-he pip€s

while designing the pneumatic system.
[Section 4.7.2] (W-l.r)

Q.d Write any four tips for good piping itr ptreuDatic
systema. [Section 4.7.4] (W-13, Srg)
OR

Q.4 What are the requirements of good comopr€ssed air

W*er plvmbi^gl [Section 4.7.4] ($12)
Q.5 Explain | 1) Sta-ndard pipe (2) Extra stmog piF.
lsection 4.7.61 ($12)

Q,6 Name any eight pipe and tube fittiagE. Write theit
tuilctiotr in briet lsechtoz 4. Z Z (W-12)
Eff,." (u"ur.) 4-87 lntrod.lo & Compon. ol Pneu. Sys.

a.A a.dr h PnsuDstlc SyatoD :

Q. 1 What ar€ the various fuDctions of seals? Write the

t,?es ofseals used.I.Section 4.8.11 (S-12, W-lg,s-ll)

Q. 2 Sketrh the cup seal, and write its applications.

tsectian 4.8.2l ($rs)
OR

Q. 2 Differ€ntiat€ b€tween static seal and dynamic seal.

tsectian 4.8.21 (a.l,r)
O. 3 State any rour reasons of lailure of pneumalic seals.

[Section4.8.3] (W-11)

a.o Ftlt3r ir Pneu.Drattu ayst.E :

Q. 1 What is tunction oI filter? How frlters are classfied?

Name atry four advantases ol b)"ass 6lt€r.
($r2, w-r2)

Q.2 Give the classification of filters used in pneumatic

syst€m. ExpIaiD aDy one oftlem. (W-fg)

otrtr
EEf,r, (r""r.) 4-88 lnlrod.to & Compon. ol Pneu. Sys-

Note
Chapter

Pneumatic Circuits

Syllabus

Speed control circuits for double acting cylinder

and bidirectional air motor
Sequencing circuits - Position based sequencing
circuit and time delay circuit
@f ,r" 1rsur.1 Pneumalic Circuils

5.1 Operatlng SAC using 3/2 DCV:

9n2
O. Drarv clntrol of slngl€ acling cylind€I pieumatic drcuh using
3x2DCval\€.
For op€rating SAC, we ua€ 3/2 DCV.
3i/2 DCV ha8 tiree ports namely iDlet port "P', tatrL port "1'
and cylinder port "A.'.
It has two positions ofits spool.

ll iritt
litlllr

TTITT

Fis.5.1.l

ID filst position of spool of32 DCV, oil under preeeue flowg

ftom P to A and T is closed. Hence the pist n ofSAC extcnds.
In second position of spool of 312 DCV, oil under prcssure
flows from A to T and P is clG€d. Heoce the ptuton of SAC
retracta.
B IFP (MSBTE) 5-3

5.2 Uni-dircctional Motor bY 3/2 DCV :

92013
O. State any two applkHions of 3 x 2 DC pneumalic valvo with
any ckcuil diagram.
Uni-directionat 6otor runs in otre direction onlv. It does not
run in the other direction.
Uni-diectional motoi can be operated by using 3/2 Direction
Control Valve.

Fig.5.2.l

. ln 6rst position of spool of 3/2 DCV, compreesed air Ilows

from P to A a-nd T b closed. Hence the shaft of the motor

. In eecond position of spool of U2 DCV, comPressd air llov{s

fioE A to T and P is closed. Hence the motor stops.
Appllcatlons ol 3f2 oCV
. To operat€ sirgle actiag cylirder.
r To operate unidirectional motor.
Fl",r" rr""r.r 5-4

5.3 Operating DAC using /U2 DCV:

s-412
O. Draw the pneuhatic circuit showing conlrol of DA cylinder
4x2DCvalve. the

For op€rating DAC, we use ,V2 DCV.

{,r2 DCV has four ports namely i et polt "P", tank port'T',
cylinder port "A" and cylitrder port "B".

It ha6 two positions ofits spool.

fl
c
I
---

Fts.5J.1

In first position ofspool of4l2 DCV, ai! flows from P t Aand

B to T. Hence the piston ofDAC extends.

ln second position spool of 4/2 DCV, air llows from P tD B

and A to T. Hence the pfuton ofDAC retracts.
ffi ,r" (rsurr) Pneumatic Circuils

5.4 Ope rating Two SAC using One 412 DCv :

,V2 DCV has two cylinder ports oaDely, cylinder Frt "A.'
If there are two single actiDg cylindeB
atrd cylinder port "8".
we catr coDlect each port to each SAC, so that, while one is
ext€nding the otier will b€ rctractin8.

4/2 DCV has two positions of its spoot.

a
a
a
a
ta
B
#
txl
T

Fie.5.4.l

In first position of spool of 4/2 DCV, air flows fiom P to A and

B to T. Hence the cylinder-l extends and cylinder-2 retlacts.

ln air flows from P to B

second position spool of 4/2 DCV,
and A to T. Hence the cylinder-2 extcnds and cylinder-l
 IFP (MSBTE) 5-6

5.5 Operating Only One SAC usin ga4l2DCV:

We know that 3, DCV is rcquir€d to op€rat€ a SAC. But, if

you dont have 3/2 DCV, a:rd inst€ad, you have a 4/2 DCV,
then, no problem, you caD use it by closing any oDe of its
cylinder ports.
a/2 DCV has two cylinder ports aamely, cylinder port 'A"
and cylinder port "B". If there is only oDe SAC, thetr we csn
colnect any one of the cylinder ports to the SAC snd plug
(close) the other cylinder port. Now the 4/2 DCV acts as 3l/2
DCV because out of 4 ports one is plugged and o y 3 are
remaining.

T!-

Ei B

Fi& 55.1

In fiIst positiod of Bpool of 4/2 DCV, air flowe from P to A and

B & T are clo8ed. Hence the SAC exteods.
In second positioD spool of !u2 DCV, air flows from A to T
and B & P are closed. H€nce the SAC r€tracts.
lql rFP 5-7 Pneumatic Circuils

5.6 Op€ratln g DAC using 4/1l DCV :

We csn use ,(3 DCV to operate DAC so as tD extend, r€hact
ard to stop atrywher€ in the middle.
4/2 DCV has four ports namely inlet port "P', tatrk port 'T"
cylirder port "A' and rylinder port "B".
It has thrce positions of its spool.

c
II
e

N
rrg.5.6.t

In frst position of spool of 412 DCv, air flows froE P to A alrd

B to T. HeDce the piston of DAC extendE.
In secoDd po€itiotr sv,,l ot 112 DCv, air flows from P to B
and A to T. Iience the piston of DAC retracts.
In middle position of the spool, the cylinder ports are closed.
Hence the cylioder atope.
Itr this erampte, the 4/3 DCV has clos€d type mid pGition.
Port-P and Dort-T arc closed iD ttre mid positioD.
We dotrt use opeD ceDter or t€trdem ceDt€r I)cV for
pDeuaatic syst2Ds, becaue€ if port-P i8 codnect€d t Port-T,
then compreesed air will be lost to atmGpher€.
 5-8 Pn€umalic Circuits

5.7 Operatin g Bi-dlrcctlonal ilotor by /V3 DCV :

w-201r, s-2012, $N13, W-2013

q. Explain with circuil diagram a pnouhatic circuit lor spo6d
control of molor.

rtx B

Fis.5.7.1

Tbe above Fig. 5.7.1 shows a ptreuDatic circuit to operate bi-

dircctionAl motor. This dotor can run in both alirections.
Itr 6rst position of,4/3 DCV, compr€ssed air flows ftoD P to A
and B to T. Hence the motor rurs in clocLwise direction.
In second position 4/3 DCV compressed air flows ftom P to B
and A to T. Hence the motor ruDs i.E arltidockwise direction.
By opeEting the llow contml valve, we ca.n vary the llow
rate of compr€ssed air and thercby, we cao control the speed

In closed center t)'pe mid position 4/3 DCV, all ports are
closed. Port A and B ar.e closed alrd Port P and port T are
also closed. Hence the motor stops.
We don't ule open cetrt€r or taDdem cent€r DCV for
pDeumatic systems, because if port-P is connect€d to port-T,
then compressed air will be lost to atmospher€.
 59 Pneumatic Circuils

5.8 Dual Control Crwo Hand Operation ) Circuit :

. This is a safety circuit named as "t$'o hand ope'ation" or

"dual cotrtrol" of cYlinde!-
. Herc, the opentor has t engag€ bot'h of his hands tog€t}€r
in operatbg the vslves for making the DAC to exteEd
. This prcvents the chance oI aclident or iniurv tD the hands of
the operator.

5.8-l Two Hand Operatlon ol SAC uslng Two 3'2 DCV

. Actually, one 3/2 DCV i-s sufficient just to operate a SAC BUt
for saf;ty of operatDls ha.ads, tbe ssfety cirtuit coD'sists of
two 3i/2 valves.
. Opemtor has t! operat€ both of these valves tDgether, tien
only the DAC extends

Fi& 5.t.1

The ciicuit coDtains two NC 3/2 valves. NC meaos, "normally

cloaed". In nomral positioq ttre inlet port "P'is closed and
cylinder port "A.' is contrected to t nk port'f'
I'lDse two valves ale contrected in series, that is, the outlet
port of first valve is connect€d to iDlet port of second valve'
Whetr both of these valves are pressd together' compFessed
air flows to SAC aDd the SAC exten&.
ffi IFP (MSBTE) 5-10

5.8.2 Two Hand Oporatlon of SAC uslng Twln pressure

Valve :

Shuttle valve has AND logic functio!.

Shuttle valve has two itrtets (port-A and port-B) and one
outlet (port-C).
Ifcompress€d air is supplied to both the two iDlet ports, then
oDly ther€will be supply froo the outlet.

T T
#
I

N
IIS.5.t.2
Circuit consists of two NC 3il2 valves, valve-l and valve.2.
Outlet of valve-1 is conBect€d to inlet-A of twio pr€s6urc

Outlet of valve-2 is comec,ted t ilrlet-B of twitr Eersu.ro

Outlet-C oft$.in pr€ssurc valve is coanected to SAC.

When both of these two 3/2 valves ar€ pr€ss€d together,
compr€ssed air flows to SAC, and the SAC extends.
Lllr IFP (MSBTE) 5-11

5.8.3 Two Hand Op€ratlon ol DAC using Two 3/2 Valves :

s-2014
312 sPring
o. Draw pneumatic circuit to operate a DAC using
rEtUfi type DCV, No other DCV should bo used tn the circuit.
in brie, and the ol lhis
Fis. 5.8.3 sbows a t*o hand oP€ration circuit for operatioD
DAC using two 3/2 spri-og returD valves'
Valve-1 is NC valve; it is oormallv clo6ed tvpe valve ln
port
dormsl positioq the inlet port "P" is clos€d, and cylinder
"A.' is connected to tsDk Port 'f.
vs.lve-2 is NO valve; it is norEslly open type valve lr!
normal poeition, the idet port "P' is connectcd to cyliDder
port "B", tsnk port'T. is clGsed.

Ft& 5'63

. DAC is in rckact€d poaition in normal Position of the 3i/2

valvea.
. For ext€ndi[g the cylinder, op€mtor has t' operate bot'h of
ttrrese two 3i/2 valves trgether.

Appucetion : lt is a safetv circuit. lt

safeguards the hands of the
operator in case ofpaeumatic press machioes'
 a 5-12 Pnoumaiic Circuils

5.9 Operati ng DAC usin g 5/2 DCV :

For opemting DAC, we can us€ S/2 DCV.

512 DCV ha! 6ve ports tramely inlet port .p", cylinder port
'A" a.Ild cylinder port "B" taDI port *T1", tank port "T2".
5/2 DCV has two positions ofits spool.

c
I--

\
T1 12

Fis.5.9.l

In first position of spool of 5D DCV, compressed ah flows

fiom P to A and B to T2. Heoc€ the piston of DAC extcnds.

In second position spool of E/2 DCV, compressed air flows

from P to B atrd A to T1. Hence the piston of DAC rctracts.
Ef ,'" MSATE) 5-13

5.10 Automatlc Continuous Operation ot DAC :

. We can use either of the following two t'p€s of circuits for

obtaining continuouB reciprocation of piston of double acting
cylinder
o By usins limit swit hes and double solenoid 4/2 DCV'
o By usirg limit valves and double pilot 'U2 DCV'
. By adjusting the positioD oflimit switrhes or liEit valves, we
can adjust the length aDd position of shoke of tle cvlinder'
Hence these cirtuitE ar€ 3160 cslled stloke contIol cir'cuits'

5.10.1 By using Limit Swltches and Double Solenold 42

T'CV :

c
n
LS1
fi
L52

s1 s2
t/
T

Fis.5.10.1

Itr this circuit a 4/2 double-solenoid DCV is used. Therc aie

two limit swikhes to opemte this 'y2 DCV. When a ltuit
switah i3 pressed, electric current flows to the cotrnected
solenoid and hence the spool ot 42 DL\J shifts to other
positio!.
The piston rod, while reciprocating, actuates these limit
switlhes, which intem actuates !U2 DCV. Thus autoEatic
reciprocation of ra:rr is achieved.
ffi'.e (MSBTE) 5-14

In first position of{"/2 DCV, compressed air flows froDr p to A

and B to T. hence the cylinder ext€nd_s. By the end of
ext€nsion, the cam fitted tD pistoa rod presses the liEit
s*'itch "I.s2". Hence, electric current flows to solenoid "S2"
and due to this, the spool of 42 DCy sbifts to second
position.
In second position ,Y2 DCV compressed air flows fiom p to B
and A to T. hence the cylinder retracts. By the etrd of
rehaction, the cam preases the limit swit h .LS1". Hence,
electric cur€nt flows to solenoid -S1" and due to this, the
spool of &2 DCV shifts to 6rst position. And tbe cycle
cotrtinues.

5.10.2 By using Limit Vatves and Doubte pitor 4/2 DCV :

1
s L\2
I

Fi8.5.10.2

In first psitiou of .V2 DCV, coBpressed air flolPs from p to A

and B to T. hence the cylinder extend!. By the end of
extension, the cam fitted to piston md pEsses the limit valve
"LVl". Hence, compr€ssed ai. flows to pilot "P1" aod due to
this, the Bpool of 4/2 DCV shifts to secoDd position.
ffi,rrru SBIE) 5,15

Ir secord position 4/2 DCV compressed air flows from P to B

s.d A t T. hence t}le cytinder retracb. By the end of
rekaction. the cam preaaes the limit vslve 'LV2" Hence,
compressed ail flov{s to pilot "P2" and due to this, the spool
of ,U2 DCV shifts to 6rst position. And t}le cycle contioues'

5.11 Sp€ed Control Circuils :

w.2lr14
Q, Explain pneumatic ckcuit lor controlling speed ol Double
Acling Cylinder with circuit diagram.
. Speed of pneumatic actuatorc caD be contmlled using flow
control valves.
. Vsrying the rat2 of flow of compressed air will vary the time
taken to fiI the cylioder alrd thuB vary the time of
coopletio! of the stmke.
. Io ptreumatic syst€m.s, met€ring is t€rmed as tllrcttliog'
. Ia thrcttling-in control, rate of floE' of compressed ai-r is
c\ontrolled at inlet ofactuator.
. h th.rcttling-out contrel, rste of fiow of compress€d air is
contDlled at exit ofactuator'
. In bleed of control, the rate of flov of compr€ss€d eir is
cotrtrolled in by-pass line, {'hich is left open to atrDosphere'
. We can do bleed_off conkol for pneuDatic systems, but it is
not prefe[€d, because compressed air is oot to be ll'a.stcd
Iike thst just by relearing it to athosphelq

5.11.1 Throttllngln Clrcutt lor DAC :

w-21r11
O. Erplain pneumatic circuit for contrclling speed ol doublo aciing
cylinder with circuit diagratn
w-2t]12
O. Orary and oxPlain pnoumalic meter in ctcuil to conlol the
ol extension.
In throttling-iD circuits, the rat€ of Iloti of compressed ail
into ttre cylinder is conholled by flow control valve. FCV u
placed at iDlet of the cylinder. Cap end Port "C" is idet for
extensiod and rod end port "R" is iDlet foi r€kaction.
E IFP (MSBIE) 5-i6 Pn€umalic Circuits

c c
II -

T T

Fis. s.ll.l
Throttlirg.h circuit lor Tbrotoing-ln circuit for
orar€a8ion retr8ctioD
In first position of 42 DCY, ID first position oI 42 DCy,
compr$sed air flowB fiom P to compr6sed air flows from P to
A aad B to T. ttri! flow is A aod B to T. this flow is
thmugh Ilow coatml valve, the throwh check valve. This is
flow is coDtrolled atrd hedce ft€e flow. Hence the pistoa
pfuton ext€ods sloli,ly. extendr at higher speed, which
is not controlled.

In second position 4/2 DCV, In s€cond position 4/2 DCV.

compresed air flows from P to compressed air flows Aom P to
B aDd A to T. this flow is B and A to T. this flow is
through check valve. ltis is thmugh flow control valve, the
free llow. HeDce the piston flow is coDtmlled and hencc
retracts at bigher sp€ed, which pistotr rctracts slowly.
is not contrclled.
ffi,r" (r""r.) 5-17

5.11.2 Throttling.out Circuit lor DAC :

w-2012
o Draw and explain pneumatic meter out circuil foa controlling
extension ol piston.
s.2014
o Draw throttling out (meler oul) pnoumatic circuit to cohtrol the
speed of retraction of OAC. Explain in brief.
In throttling'out circuit€, th€ rut€ of flow
of compressed air
comiDg out of thecylnder is controlled by flow control valve.
FCV is placed at outlet of the cylinder. Rod end port "R is
outlet for exteNion and cap end port "C" is outlet lor
retraction.

B B

lig.5.ll.2
Throttling-out circuit for
Ttrottling.out circuit for
extension retraction
In first positio ot 42 DCV, In firct position oI 412 DCV,
compressed air flows from P to compressed air flows from P to
A aad B to T. this flow is A and B t T. this flow is
through florv control valve, the through check valve. I'his is
flow is contrclled and hence free flow. Hence the piston
piston ext€nds slowly. extends at higher speed, which
is not cotrtrolled.
llz IFP (MSBTE) 5-18 Pneumatic circurts

Throttlin8-out cifcuit for Ttrrottling.out circuit for

ertenrion retrsction
In second position 4/2 DCV, In second position 4,/2 DCV,
compressed air: flowsfroE P to coEpress€d ail flows from P t
B and A t T. this flow is B and A to T. this flow iB
thmugh check valve. This is through flow coatml valve, the
free tlow. Hence the pistolr flow is cootmlled aDd heirce
rchacts at higher speed, which piston retrscts slowly.
is not conholled.

5.'11.3 Bleed-off Circuit :

In bleed-of control circuits, a by-pass line is coDtrected to

inlet of cylinder.
Cap end port "C" is i-nlet for extensiotr and rcd end port "R" is
inl€t lor retraction. Flow control valv€ is placed in this
brpass line.
This FCV allows conholled amount of compressed air to flow
to atmosphere. Hence only the remaining amount offlow can
flow into the cylioder.

c c
-

Fie.5.l1.3
lql rFP 5-19 Pneumalic Circuits

Bleed-off cirsuit for Bleed-ofi cir€uit for

e:densioD r€tractiorr

In 6rst position ol 42 DCY, Itr fir€t position ot 42 DCY,

compressed air flows filom P to compmssed air Ilows from P to
A ald B t T. But this llorv A aod B to T. This fiow is fre€
coEtrolled flow because a flow. lhere tu no FCv in tlis
conholled amount of lhe. Hence the piston extpn&
compressed air is releaeed to at high speed, which is not
atmospherc tlEough FCV. controlled.
ODly the remsining arnount of
compres6ed arr is flowing in to
the cylinder. HeDce t-he piston
extends slowly.

In second poBition 4/2 DCV In second position 4/2 DCV

compr€$ed air Ilows from P to comprcssed ai! flows from P to
B aDd A to T. this llow is ftee B ard A tD T. But this flow
flow. there is no FCV in this contmlled flow because a
line. HeDce the pistoD retracts contmlled amoutrt oI
at high speed, which tu not compressed air is released to
controlled. atmosphere through FCv.
Only the remaining amouDt of
compressed air is flowing in to
the cylinder. Hence the pisto
rctlact€ slowly.

Bleed-of contml is not Feferr€d for pneumatic syst€ms,

because compressed air i3 not to be wast€d like that just by
releasing it to atmmphere.
ffi,r" (rs"r.) 520

5.12 Sequencin g Circuits using Sequence Valves:

. ID pneumatic circuits, use ofsequence valve is not that much
popular, because it iB difficult to set the cracking pressure of
sequencing valve withia the available small range of air
pressurc (appmximately 0,5 bar).
. Sequence valves are exteNively used in hydmulic systems.
. But, as a part of study, we shatl go thmugh a simple circuit
using sequence valve in pneumatic system.
Circuil to Opomte Two SAC ln Sequence :

a :l #
T

Fig.5.l2.l
When lever oI3/2 DCV is in fiIst position, comprcssed air is
supplied t inlet port of sequence valve. It llows dircctly to
outlet portl. Hence cylinder-l extends fiIst.
By the end of extensio[ of cfliDder-l, pressurc in the line
increases and hence the poppet of sequence vslve Iifts of
Iiod its 6eat to allow coEpressed air to flow to port2, helce
cylinder-2 extends.
When the lever of 3/2 DCV is shified to second position, both
cylinders retract simultareously.
ffi ,r, (r""r.) 5-21

5.13 Sequencing Circuits using Limit Valves :

In the above examples, sequencing is executed due to the

prcssurc increase at the end of op€rations. ltese are
pressure-controlled sequencing circuits.
But now what we study is positioa-conholled sequenci g
circuits, here the sequencing is achieved due to the position
ofpiston.
Limit valve is a cam operated spring retum 3/2 direction

5.13.1 Operate a SAC and a DAC in Sequence:

s-2012
O. Explain with neat sketch sequencing ol SAC and DAC usjng
roller operated dkection control valve.
In firut position of lever of 4/2 DCV, the DAC extends. By the
end of extension of DAC, the carD presses tie limit valve,
hence compressed air flows to SAC, atrd SAC extends,
When the Iever of4l2 DCV is shifted t! second positioo, DAC
retracts, and simultaneously, the SAC will also rehact.

II
oAc

c l
-
F
B LV1
2
T

Fig.5.l3.l
ffi ,r" (r""r.) 5.22

5.13.2 To Operate Two DAC in Sequence :

s-201r, s-2013
O. Explain with neal sketch, $rorking of sequencing circuil for two
double acting air cylinders.

In ffrst positiotr of lever of ,t2 DCV, the DAC extpnds. By t,}re

erld of extension offil8t DAC, the cam press limit valve Lv1,
hence compressed air flows to secood DAC, and aecond DAC

extends,
'When
the lever of,U2 DCV tu shifi€d t Becond position, DAC

rehacts. By the end of retraction of fir3t DAC, the csm press

limit valve LV2, hence compressed air llows to seeond DAC,
and secotrd DAC retracts.

C
rt= 1

B
LV2 LV1

ffi
Fis.5.13.2
Efl rFP MSBTE 5-23

5.'14 Seq uencing Circuits using Limit Switches :

Limit switch is an electrical swit h which when pressed by

any mo\.ing element, it makes the electrical coDnection, and thus
electric cunent flows to the electric device such as motor, soleDoid,

5.14.1 To Operate a SAC and a DAC ln Sequence :

c
fi
LSl

ri& 5.14.1

In first positioa oflever of4l2 DCV, the DAC extends. By the

erld of extension of DAC, the ca]n press limit switch LSl,
electric cuirent flows to solenoid 51, spool of 3/2 DCV shifts
to s€cond positioE, hence compreeeed air floes to SAC, and
SAC extends.

Whetr the lever of ,U2 DCV is shiftDd to second Position, DAC

retracts, and simultatreously, the SAC will also retract.

llUl rFp (MsBrE) 5-24 Pnoumalic Circuils

5.14.2 To Operate Two OAC in Sequence

LS1
T
a E!t
I]X T
2

S1 S2

lig.5.l{.2
In first position of lever of 4,/2 DCV, the first DAC exteDds.
By the end of extension of fiIst DAC, the cam Fess limit
svritrh lS1, hence compressed air llows to port-1 of second
DAC, and second DAC extendB.

When the Iever of 4/2 DCV is shifted to second position, Erst

DAC rctracts. By the end of retraction of frrst DAC, the cam
press limit swikh lS2, hence compressed air flows to port-2
olsecond DAC, and second DAC retracts

5.15 lmpulse Operated Pneumatic Circuit;

*m12
O. Oraw impulse pneumalic circult and explain.
w-2t11,9-2013
O. What is impulse circuit ? Explain.
w-m13
O. Explain with sk€tch, wo*ing ol impulse operation pn€umalic
circuit.
ffi,r, tt"rr.t 525 Pneumatic Circuits

Lopulse operatioD means "operatioo of t}le E.in valve

using the impulse of an impulse velve".

The circuit has two valves : Main valve and iEpuls€ velv€.
Main vslve is a single pilot operat€d spring rett,In tt'P' A2
direction contrcl valve.

Impulee valve is palE buttoD operat€d spring retum tJrpe

3,4 direction control valve.

Fis.5.ls.l

In normal positioD of valves, the DAC i.s in retracted

position.

When the palm button of iEpulse valve ia pressed

manually, compressed air llovrs to the pilot port of mrin
valvc. Hence, the spool of DAin vslve rill be shifted to the
s€cord positiotr. I'he DAC extetr&.
[ff ,r" 1r"u-.1 5,26 Pneumatic Circuils

5.16 Pneumatic Circuit using Quick Exhausl Valve:

f--
e\ )@
B

Fi8.5.r6.r

Fig. 5.16.1 shows circuit diagram using quick e).haust valve.

In tust position of ,V2 DCV, compressed air flows from P to

A. Air present in the rod end side of th€ cylinder is exhausted to
atmosphere at the quick exhaust valve (2).

In second position of tY2 DCV, compressed air Ilows from P to

B. Air present in the head end ofth€ cylhder is exhausted to
side
atmosphere through quick exhaust valve (l).
W IFP {MSBTE)
5.17 Time Delay Valve Circuil :

T
il

Fig.5.l7.l
when the push button of 3i/2 valve "A" is pre$ed,
compressed air flows to intet of time delay v8lve.
It fiows through the check valve and quickly ills in tbe
r€servoir. It exets priessune on tlle spool of pilot operated
'2
valve, hence the spool will shift to make the connection from inlet
"P' to cylinder port "A.' and hence the single acting cylinder

When the push button of 3ll2 vatve i-s released, the spool oI
pilot operatcd 3/2 valve will not shift bsck until the pr€8sute in
reservoir falls below the spring force. CoEpiessed air is leaking
slowly througtr the llow coDtrol valve and hence pnessur€ is
&opping slowly.
Once the pressure trecodes less thar! the spring Prressute, the
spool wil shift back automatiBlly to close the idet, and makeg
coDDection from cylinder Dort "A" to outlet port 'I", hencc t,}te
cylinder retlacts.
I}te tiDe of deley cqn be easily adju3trd by sdjBtitrg the
Ilow cootrol valve.
@]",r" 1rs"re1 5-28 Pneumalic Circuils

5.18 lmportant Examination Ouestions and

Answers

Please refer ebook for complete solution

Note :
I Please download our free e-bak for detailed. answers
of follnuina que stions.
2 All Questions & Ansuerc cooer the conplete chdpter.

6.t OpcrattDg SAC Esrrg Sr, tlc.g

Q- I Draw control of single acting cylinder pDeumatic
c cuitusing3x2Dcvalve. ($12)
6.C Opor.tlDg UDldlt.ootloDrl Uotor by g,/g DCV

Q. 1 State aEy two applications of 3 x 2 DC pneumatic

valvewiti any circuit diagram. (S1g)
6.a Op.ratlnS DAC u3lng,Ug DCV
Q. 1 Drav{ the pneumsti€ circuit showing control of DA
cylinder using 4 x 2 DC valve. Explain the worhing.
($12)
6.7 Op.irtlng BtdlrcouoD.al Uotor uatDg.Mt DlcV
Q. t Explaitr with circuit diagram a pDeumatic circuit foi
cortrol of bi directional motor.
speed
(w.11, $12, S.r3, W-r3)
6.a Irurl Contrcl (T*o E.rd Op€rstlon) Ctrilltt
Q. 1 Draw pneumatic circuit to operate e DAC using two
3i/2 spring rcturn t)'pe DCV. No other DCV should be
used in tlle circuit. Explain in brief and stat€ the
application ofthis ciiluit, tsection S.B.gl (gf4)
6.11 6ll'6od Control ClEutts

Q. 1 ExplaiD pneumatic circuit for conholling speed of

double scting cylinder with circuit diagram. (W-11)
ffi,t" tr"ut.t 5-29

OR

Q. r Explain pneumatic circuit for (onrrolling speed of

Double Actins Cylinder with circuit diagram. (W'r4)

OR

Q. 1 Draw and exptain pneumatic met€r in circuit to

control the speed ofextension. (W-12)

Q.2 Dra$ and exPlain pneumatic meter out ctcuit for

controlling extension of pistnn. [Section 5.112] (W'lzl
OR

Q.2Draw throttling out (meter out) pneumatic circuit to

contrcl the speed of rehactioD of DAC. Explain in
bief. tsection 5.11 21 (S'14)

6.13 SequoD4l.ng Cttcrtt3 usirg ll.Dlt Valv63

Q. 1 Explain with neat sketch sequeDcirg ofSAC and DAC
using rollet operated direction control valve. (S'12)
[Section 5.13.1]
Q.2 Explain with neat sketch, working of sequencing
cicuit for two double acting air cvlinders. (S'fl'S13)
[Section 5.13.2]
5.rf IrDDulso Op€ret d Ptreum.tlc Cttsutt
Q. 1 Draw impulse pneumatic circurt and explain.
(s-12, W.rr, s-ls)
OR

Q. 1 Erplaia with sket h, worki.Dg of impulse operation

pDeumatic cirsuit. (W'fg)

ooo
ffi IFP (MSBTE) 5-30

Note
Appendix
 A

ASTM D2270 Table

L and H values for oil ofkinematic viscosity at 100 "C

L II L II L H

(cSt) (cSt) (cSt) (cSt) (cSt) (cst) (cSt) (cSt) (cSt)

2.00 7.994 6.394 4.40 30.48 6.80 73.48 46.44

2.to 8.640 6.894 4.50 31.96 23.81 6.90 75.72 47.51

2.20 9.309 7.4tO 4.60 24.71 ?.00 78.00 44.57

2.30 10.00 ?.914 4.70 25.63 ?.10 80.25 49.61

2.40 10.71 8.496 4.80 36.79 26.57 7.20 82.39 50.69

2.50 11.45 9.063 4.90 38.50 27,53 7.30 84.53 51.78

2.60 t2.21 9.7 5.00 40.23 28.49 7.40 86.66 52.88

2.70 13.00 to.25 5.10 41.99 29.46 7.50 88.85 63.98

2.80 13.80 10.87 5.20 43.76 30.43 7.60 91.04 55.09

2.90 14.63 11.50 5.30 45.53 31.40 7.70 93.20 56.20

3.00 15.49 L2.15 5.40 4',7.31 32.3? 7.80 95.43 57.31

3.10 16.36 t2.82 5.50 49.09 33.34 7.90 97.72 58.45

3.20 17.26 13.51 5.60 50.87 31.32 8.00 100.0 59.60

ffi,." 1r"" TE) A-2

L H L II L H

(cSt) (cst) (cSt) (cSt) (cst) (cSt) (cSt) (cSt) (cSt)

3.30 18.18 14.21 5.70 52.64 35.29 8.10 102.3 60.74

3.40 19.12 14.93 5.80 54.42 36.26 8.20 104.6 61.89

3.50 20.09 15.66 s.90 56.20 8.30 106.9 63.05

3.60 21.08 16.42 6.00 57.97 38.19 8.40 109.2 64_18

3.70 22.09 17.19 6.10 59.74 39.17 8.50 111.5 65.32

3.80 23.13 17.97 6.20 6t.52 40.15 8.60 113.9 66.48

3.90 24.19 14.77 6.30 63.32 41.13 8.70 116.2 67.64

4.00 25.32 19.56 6.40 65.18 42.14 8.80 118.5 68.79

4.10 26.50 20.37 6.50 67.t2 43.18 8.90 120.9 69.94

4.20 21.21 6.60 69.16 u.24 9.00 123.3 71.10

4.30 29.O7 22.05 7L.29 45.33 9.10 125.1 72.27

9.20 128.0 73.42 11.8 1.2 105.4 14.1 276.3 141.0

9.30 130.4 74.57 11.9 199.0 106.? 14.5 279.6 142.4

9.40 132.8 15.73 12.0 201.9 108.0 14.6 283.0 143.9

9.50 135.3 76.91 12.1 204.8 109.4 14.7 286.4 145.3

9.60 137.'.l 78.08 t2.2 207.8 110.7 14.8 289.7 146.8

9.70 140.1 79.27 12.3 21o.7 t12.O 14.9 293.0 l4a.2

9.80 t42.7 80.46 12,4 2t3.6 113.3 15.0 296.5 t49.7
9.90 !45.2 81.67 12.5 2t6.6 114.7 15.1 300.0 151.2
 BTE) a-3 App6ndix

L H L H L H

(cst) (cst) (cSt) (cSt) (cst) (cst) (cSt) (cst) (cst)

10.0 147.7 42.47 72,6 2t9,6 116.0 15.2 303.4 152.8

10.1 150.3 84.08 t2.7 222.6 1t7.4 15.3 306.9 154.1

10.2 152.9 85.30 12.8 225.7 118.7 15.4 310.3 155.6

10.3 155.4 86.51 t2.g 228.8 120.1 15.5 313.9 157.0

10.4 158.0 87.72 13.0 231.9 121.5 15.6 317.5 158.6

10.5 160.6 88.95 13.1 235.0 122.9 t5.7 32t.1 160.1

10.6 163.2 90.19 13.2 238.1 124.2 15.8 324.6 161.6

10.7 165.8 91.40 13.3 241.2 t25.6 15.9 328.3 163.1

10.8 168.5 92.65 13.4 214.3 t27.0 16.0 331.9 164.6

10.9 171.2 93.92 13.5 247,4 128.4 16.1 335.5 166.1

11.0 173.9 95.19 13.6 250.6 129.8 16.2 339.2 167.7

11.1 1?6.6 96.45 1S.? 253.4 131.2 16.3 342.9 169.2

tl.2 t79.4 97.71 13.8 257.0 132.6 16.4 346.6 170.7

11.3 182.t 98,97 13.9 260.1 134.0 16.5 350.3 172.s

11.4 184.9 100.2 14.0 263.3 135.4 16.6 354.1 173.8

11.5 187.6 101.5 14.1 266.6 136.8 16.7 358.0 t75.4

11.6 190.4 102.8 t4.2 269.8 138.2 16.8 361.7 r77.0

lt.? 193.3 104.1 14.3 273.0 139.6 16.9 365.6 178.6

17.0 369.4 180.2 19.6 475.7 222.8 24.4 704.2 309.4

l(Yl rFP (MSBTE)

L H L II L II

(cSt) (cSt) (cSt) (cSt) (cSt) (cSt) (cSt) (cst) (cst)

17.1 181.7 19.7 479.7 224.5 24.6 ?14.9 313.0
17.2 377.1 183.3 r9.8 483.9 226.2 24.a 725.7 317.O

17.3 381.0 184.9 19.9 488.6 25.O 736.5 320.9

17.4 384.9 186.5 20.0 493.2 229.5 25.2 s24.9

17.5 388.9 188.1 20.2 501.5 233.0 25.4 754.2 328.8

17.6 392.7 189.7 20.4 510.8 236.4 25.6 769.3 332.7

17.7 396.7 191.3 20.6 519.9 240.1 25.A 779.7 336.?

17.8 400.7 192.9 20.8 528.8 243.5 26.0 790.4 340.5

17.9 404.6 194.6 21.0 538.4 24?.1 26.2 801.6 341.4

18.0 408.6 196.2 21.2 547.5 250.7 26.4 812.8 94a.4

18.1 412.6 197.8 21.4 556.7 254.2 26.6 424.1

14.2 416.7 199.4 21.6 566.4 257.a 26.8 835.5 356.4

18.3 420.7 201.0 21.8 575.6 261.5 27.0 847.0 360.5

18.4 424.9 202.6 585.2 264.9 27.2 857.5 364.6

18.5 429.O 204.3 595.0 258.6 27.4 869.0 368.3

18.6 433.2 205.9 22.4 604.3 27.6 880.6 372.3

18.7 437.3 207.6 22.6 614.2 275.a 892.3 376.4

18.8 u1.s 209.3 22.a 624.1 279.6 28.0 904.1 380.6

18.9 445.7 211.0 23.O 633.6 283.3 28.2 915.8 384.6

@ BTE)

L fl L 11 L n

(cSt) (cSt) (cst) (cst) (cst) (cSt) (cSt) (cst) (cgt)

19.0 .149.9 2t2.7 613.4 286.8 24.4 927.6 388.8

19.1 454.2 214.4 23.4 653.8 290.5 28.6 938.6 393.0

19.2 458.4 216.1 25.6 663.3 294.4 2a.8 951.2 396.6

19.3 462.1 217.7 23.8 613.7 297.9 29.0 963.4 401.1

19.4 1$7.0 219.4 24.0 683.9 301.8 29.2 975.4 405.3

19.5 471.3 221.t 24.2 694.5 305.6 29.4 987.1 409.5

29.6 998.9 413.5 42.O 1892 701.9 55.0 3L26 1066

29.8 1011 417.6 42.5 1935 714.9 3180 1082

30.0 1023 42t.7 43.0 1978 724.2 56.0 3233 1097

30.5 1055 492.4 43.5 2021 741.3 56.5 3286 1112

31.0 1086 443.2 44.0 2064 754.4 57.0 3340 7127

31.5 1119 454.0 u.5 2108 767.6 57.5 3396 1143

32.O 1151 464.9 45.0 2152 780.9 58.0 3452 1159

1184 475.9 45.5 2t97 794.5 58.5 3507 1175

33.0 l2l7 487.0 46.0 2243 808.2 59.0 3563 1190

33.5 1251 498.1 46.5 22aA 821.9 59.5 3619 1206

34.0 1286 509.6 47.0 835.5 60.0 3676 1222

34.5 132r 521.1 47.5 2380 849.2 60.5 3734 1238

35.0 1356 532.5 48.0 2426 863.0 61.0 3792 t254

ffi ,." (rusare) A6

L E L E L H

(eSt) (cst) (cSt) (cst) (cst) (cSt) (cst) (eSt) (cSt)

35.5 1391 5M.0 48.5 2473 876.9 61.5 3850 1270

36.0 1427 555.6 49.0 252t 890.9 62.O 3908 1286

36.5 14U 567.1 49.5 2570 905.3 62.5 3966 1303

37.0 1501 579.3 50.0 2618 919.6 63.0 4026 1319

37.5 1538 591.3 50.5 2667 933.6 63.5 4087 1336

38.0 1575 603.1 51.0 27t7 948.2 64.0 4147 1352

38.5 1613 615.0 51.5 2767 962.9 64.5 4207 1369

39.0 1651 627.1 52.0 2817 977.5 65.0 4268 1386

39.5 1691 639.2 52.5 2867 992.1 65.5 4329 1402

40.0 1730 651.8 5S.0 2918 1007 66.0 4392 1419

40.5 1770 664.2 53.5 2969 1021 66.5 4455 1436

41.O 1810 54.0 3020 1036 67.0 4517 1454

47.5 1851 689.1 54.5 30?3 1051 67.5 4580 1471

otro
 Appendix B
Fluid Power SYmbols

Pumps and compressors:

Hydraulic pump Air compteasor

Unidirectional

(b) Bidirectional

(c) Variable delivery

unidirectional

(d) Variable delivery

Bi-directional

Hydraulic molors and pneumalic motors :

Hydrsulic Motor Air Motor

(a) Unidirectional

(b) Bi-dircctional

(c) Variable spe€d

unidirectional
 B-2 B

Hydraulic Motor Air Motor

(d) Variable speed
Bi-directional

Cylinders i
(a) Single acting Spring return t)pe (b) Gravity
cylinder retum
\cf tvpe

(b) Double acting

Ir=
Single rod end t54r Double rod end tl'pe
cylinder

(c) Rotatirg
cylinder

Valves :
(A) Pressure control valves :
(a) Pressure relief valve I

(b) Sequence valve with

1

reverse free flow

2 IN
ffi,t, (u""r.r App€ndix B

(c) Pressure reducing valve

(B) Diiection control valveB !

(a) Check valve

(b) 212 valve

I
(c) 3/2 valve

(d) 42 valve

(e) 4/3 valve

Types of mid positions

trr
Open center

Closed center

Tandem center

Regenerative center
B IFP (MSBTE) B-4 Appendix B

Float center

5/2 ralve

(C) Flow control valves :

(a) Fixed restriction flovr

control valve

(b) Variable rcstriction llow

conhol valve l--
(c) Variable FCV with Everse
free flow

(d) Pressure compemated

variable FCV with reve$e
free flow

(e) Temperature and Pressure

comp€nsated variable FCV
with reverse free flow

Flow meter
m IFP (MSBTE) B-5 B

Methods ol operation of control valves :

(a) Det€nt twe

{
(b) Sping return t}?e

"[
(c) Hand lever operated

\r
(d) Palm button oPemted

F[
(o
Foot pedsl operatcd

Roller (Cam) opemted

I
(c) Pilot operated

rh) Solenoid operat€d

{
ftff,re (MSBTE) B-6 B

Reservoir, sump

Working line or pipe line

Pilot line

Flexiblo pipe line

Junction ofpipe lines

Jump : TSo pipelines not

connect€d but cmsses over
each other

FRJ, unit :

Simplified spnbol

Detailed symbol
ffi ,." (r.rr.) B] Appendix B

Shuttle valve c
B

Quick exhaust valve )

E

lvin pressure valve c

Time delay valve

Decelemtion valve
(Cam opemted FCV)

Dead weight Spnns loaded cas loaded

ffi,." (,rsere) B8 Appendix B

Quick Connect -,_l<o-

coupling Disconnect +€
Heat exchanger - Hester
(for heating the hydraulic oil)

Heat exchanger ' cooler

(for cooling the hydraulic oil)

Air dryer

Mufner

Flow divider
50./.

Pilot to open check valve

Pilot to close check valve

ffi ,t" tr""r.) B9 Appendix B

lmport ant Examination Questions and Answers

Please refer ebook for complete solution

1 Pleose d.ownload our free e'booh fo. detailed. ansuerB

of followina questions.

2 AU Questinns & Aasuers cooer thc conlPlete chapter.

Q. 1 Druw the symbols ofthe following: (W-2014)

(i) Prcssure compensat€d llolv control valve

(ii) FIow divider
(iii) Double acting cylinder
(iv) 4/2 direction contml valve

q.2 List the function offollowing: (W-20f4)

(i) H€at exchaBg€r

Q.3 Dlaw the symbols ofthe follo*ing: (W-201'f)

(i) Mumer
(ii) Air receiver
(iii) 32 D.C. valve
(iv) Shuttle valve

tltrD
@rre B-10 Appendix B

Note