SECTION 6 WORK EQUIPMENT

Group 1 Structure and Function ----------------------------------------------------------------------------------- 6-1

Group 2 Operational Checks and Troubleshooting ----------------------------------------------------- 6-42
Group 3 Tests and Adjustments ----------------------------------------------------------------------------------- 6-53
Group 4 Disassembly and Assembly --------------------------------------------------------------------------- 6-68
 SECTION 6 WORK EQUIPMENT
GROUP 1 STRUCTURE AND FUNCTION

1. HYDRAULIC SYSTEM OUTLINE

The loader hydraulic system is a pilot operated, closed center system which is supplied with flow
from the variable displacement piston main hydraulic pump.
The loader system components are :
·Main pump
·Main control valve
·Bucket cylinder
·Boom cylinders
·Remote control valve (Pilot control valve)
·Safety valve

Flow from the main hydraulic pump not used by the steering system leaves the steering valve
(EHPS) EF port.
It flows to the inlet port plate of two section or three section block type main control valve.
The main control valve is load pressure independent flow distribution system which routes flow to the
boom, bucket or auxiliary cylinders (not shown) when the respective spools are shifted.
Flow from the main pump is routed to the main control valve where pump outlet pressure is reduced
to pilot circuit pressure. The main control valve flow to the remote control valve.
The remote control valve routed flow to either end of each spool valve section in the main control
valve to control spool stroke.
A accumulator mounted on safety valve supplies a secondary pressure source to operated remote
control valve so the boom can be lowered if the engine is off.
The return circuit for the main hydraulic system have return filter inside the hydraulic tank. The return
filter uses a filter element and a bypass valve. The bypass valve is located in the upside of filter.

6-1
 2. HYDRAULIC CIRCUIT
36
13 12
29

PS
T X1 RH
35 MX

29

PS
a2 a3
LS
B A
T P a1 A1 B1 A2 B2 pst A3 B3
3
14

Down Floating
LH RH

Dump
6

Roll back
9 Bucket Boom Aux

Up
S1
8
CL CR
7' 7 S2
ELECTRONICS
b1 A2 B2
2 4 L

R LH
b2 b3

1 3
12
Ps
4 B.D/F B.U CRAWD DUMP

Ts T P
1 3 4 2 1.1 2.1
EF P LS T PARKING
T/M

19
B 39 B FRONT
28 28 10
A1

3 2
17 16 P1
A1
DR A DR A T1
1

L R 15 P2 20 AXLE
5 11 S1
16 B1 A1 B2 A2
T2
A2
P1 T
X1 X2
A3
X3 18
PS

T1 REAR
PS
B
37
18
PS

P T PS1
X1 X2
P T
32 34 29 PS 22 A B
S
P 38
33 27
PS

T P T
M B1 B2
P1
1 23
24 2 M 30 L
E/G E/G P
31 M 25 26
T
S1 L2 L1 S2 L4 L3 21

76096WE01

1 Main pump 14 Steering cylinder 28 Check valve

2 Fan & brake pump 15 Cut-off valve 29 Pressure sensor
3 Main control valve 16 Accumulator 30 Fan motor
4 Remote control valve 17 Accumulator 31 Pump motor (opt)
5 Steering unit 18 Pressure sensor 32 Check block (opt)
6 Cushion valve 19 Brake valve 33 Pressure sensor (opt)
7 Steering valve (EHPS) 20 Pressure switch 34 Check valve (opt)
7' Electric steering valve (opt) 21 Hydraulic tank 35 Ride control valve (opt)
8 Controller (opt) 22 Air breather 36 Accumulator (opt)
9 Joystick (opt) 23 Return filter 37 Quick coupler cylinder (opt)
10 Safety valve 24 By pass valve 38 Solenoid valve (opt)
11 Shuttle valve 25 Strainer 39 Stop valve (opt)
12 Boom cylinder 26 Oil cooler
13 Bucket cylinder 27 Pressure filter

6-2
3. WORK EQUIPMENT HYDRAULIC CIRCUIT

13 12
29

PS
RH

29

PS
a2 a3
LS

3 T P a1 A1 B1 A2 B2 pst A3 B3

Down Floating
Dump
Roll back
Bucket Boom Aux

Up
S1

S2
b1 A2 B2

LH
b2 b3

12
4 B.D/F B.U CRAWD DUMP

T P
1 3 4 2 1.1 2.1

Steering valve 28 28 10
A1

(EHPS) EF port 3 2

Steering valve 11 S1
(EHPS) LS port X1 X2
P1 T

X3

Return line

X1 X2 Return line
PS 22
Steering system

B1 B2
1 23
24
E/G
25
S1 L2 L1 S2 L4 L3 21
Fan & brake pump

76096WE02

1 Main pump 12 Boom cylinder 24 Bypass valve

3 Main control valve 13 Bucket cylinder 25 Strainer
4 Remote control valve 21 Hydraulic tank 28 Check valve
10 Safety valve 22 Air breather 29 Pressure sensor
11 Shuttle valve 23 Return filter

6-3
 1) WHEN THE RCV LEVER IS IN THE RAISE POSITION

13 12
29

PS
RH

29

PS
a2 a3
LS

3 T P a1 A1 B1 A2 B2 pst A3 B3

Down Floating
Dump
Roll back
Bucket Aux
Boom

Up
S1

S2
b1 A2 B2

LH
b2 b3

12
4 B.D/F B.U CRAWD DUMP

T P
1 3 4 2 1.1 2.1

Steering valve 28 28 10
A1

(EHPS) EF port 3 2

Steering valve 11 S1
(EHPS) LS port X1 X2
P1 T

X3

Return line

X1 X2 Return line
PS 22
Steering system

B1 B2
1 23
24
E/G
25
S1 L2 L1 S2 L4 L3 21
Fan & brake pump

76096WE03

· When the RCV lever (4) is pulled back, the boom spool is moved to raise position by pilot oil
pressure from port 3 of RCV.
· The oil from main pump (1) flows into main control valve (3) and then goes to the large chamber of
boom cylinder (12).
· The oil from the small chamber of boom cylinder (12) returns to hydraulic oil tank (21) through the
boom spool at the same time.
· When this happens, the boom goes up.

6-4
2) WHEN THE RCV LEVER IS IN THE LOWER POSITION

13 12
29

PS
RH

29

PS
a2 a3
LS

3 T P a1 A1 B1 A2 B2 pst A3 B3

Floating
Dump
Boom

Down
Roll back
Bucket Aux

Up
S1

S2
b1 A2 B2
Regeneration
check valve
LH
b2 b3

12
4 B.D/F B.U CRAWD DUMP

T P
1 3 4 2 1.1 2.1

Steering valve 28 28 10
A1

(EHPS) EF port 3 2

Steering valve 11 S1
(EHPS) LS port X1 X2
P1 T

X3

Return line

X1 X2 Return line
PS 22
Steering system

B1 B2
1 23
24
E/G
25
S1 L2 L1 S2 L4 L3 21
Fan & brake pump
76096WE04

· When the RCV lever (4) is pushed forward, the boom spool is moved to lower position by pilot
pressure.
· The oil from main pump (1) flows into main control valve (3) and then goes to small chamber of
boom cylinder (12).
· The oil returned from large chamber of boom cylinder (12) returns to hydraulic tank (21) through
the boom spool at the same time.
· When the lowering speed of boom is faster, the return oil from the large chamber of boom cylinder
combines with the oil from the pump through the regeneration check valve, and flows into the small
chamber of the cylinder.
This prevents cylinder cavitation by the negative pressure when the pump flow cannot match the
boom down speed.

6-5
 3) WHEN THE RCV LEVER IS IN THE FLOAT POSITION

13 12
29

PS
RH

29

PS
a2 a3
LS

3 T P a1 A1 B1 A2 B2 pst A3 B3

Floating
Dump

Down
Roll back
Bucket Boom Aux

Up
S1

S2
b1 A2 B2

LH
b2 b3

12
4 B.D/F B.U CRAWD DUMP

T P
1 3 4 2 1.1 2.1

Steering valve 28 28 10
A1

(EHPS) EF port 3 2

Steering valve 11 S1
(EHPS) LS port X1 X2
P1 T

X3

Return line

X1 X2 Return line
PS 22
Steering system

B1 B2
1 23
24
E/G
25
S1 L2 L1 S2 L4 L3 21
Fan & brake pump

76096WE05

· When the RCV lever (4) is pushed further forward from the lower position, the pilot pressure
reaches to 13~15bar, then the boom spool is moved to floating position.
· The work ports (A2), (B2) and the small chamber and the large chamber are connected to the
return passage, so the boom will be lowered due to it's own weight.
· In this condition, when the bucket is in contact with the ground, it can be move up and down in
accordance with the shape of the ground.

6-6
 4) WHEN THE RCV LEVER IS IN THE DUMP POSITION

13 12
29

PS
RH

29

PS
a2 a3
LS

3 T P a1 A1 B1 A2 B2 pst A3 B3

Down Floating
Dump
Roll back

Up
Bucket Boom Aux

S1

S2
b1 A2 B2
Regeneration
check valve
LH
b2 b3

12
4 B.D/F B.U CRAWD DUMP

T P
1 3 4 2 1.1 2.1

Steering valve 28 28 10
A1

(EHPS) EF port 3 2

Steering valve 11 S1
(EHPS) LS port X1 X2
P1 T

X3

Return line

X1 X2 Return line
PS 22
Steering system

B1 B2
1 23
24
E/G
25
S1 L2 L1 S2 L4 L3 21
Fan & brake pump

76096WE06

· If the RCV lever (4) is pushed right, the bucket spool is moved to dump position by pilot oil pressure
from port 2 of RCV.
· The oil from main pump (1) flows into main control valve (3) and then goes to the small chamber of
bucket cylinder (13).
· The oil at the large chamber of bucket cylinder (13) returns to hydraulic tank (21).
· When this happens, the bucket is dumped.
· When the dumping speed of bucket is faster, the oil returned from the large chamber of bucket
cylinder combines with the oil from the pump, and flows into the small chamber of the cylinder.
This prevents cylinder cavitation by the negative pressure when the pump flow cannot match the
bucket dump speed.

6-7
 5) WHEN THE RCV LEVER IS IN THE ROLL BACK (retract) POSITION

13 12
29

PS
RH

29

PS
a2 a3
LS

3 T P a1 A1 B1 A2 B2 pst A3 B3

Down Floating
Dump
Roll back

Up
Boom Aux

S1
Bucket

S2
b1 A2 B2

LH
b2 b3

12
4 B.D/F B.U CRAWD DUMP

T P
1 3 4 2 1.1 2.1

Steering valve 28 28 10
A1

(EHPS) EF port 3 2

Steering valve 11 S1
(EHPS) LS port X1 X2
P1 T

X3

Return line

X1 X2 Return line
PS 22
Steering system

B1 B2
1 23
24
E/G
25
S1 L2 L1 S2 L4 L3 21
Fan & brake pump

76096WE07

· If the RCV lever (4) is pulled left, the bucket spool is moved to roll back position by pilot oil pressure
from port 4 of RCV.
· The oil from main pump (1) flows into main control valve (3) and then goes to the large chamber of
bucket cylinder.
· The oil at the chamber of bucket cylinder (13) returns to hydraulic tank (21).
· When this happens, the bucket roll back.

6-8
3. MAIN PUMP
1) STRUCTURE (1/2)
This variable displacement piston pump consists of steering pump and loader pump.

L1 X1 B1 L3 X2 B2

L2 S1 L4 S2

X1 X2

B1 B2

E/G

S1 L2 L1 S2 L4 L3
Hydraulic circuit

76096WE88

Port Port name Port size

B1 Pressure port SAE 1"
B2 Pressure port SAE 1"
S1 Suction port SAE 2"
S2 Suction port SAE 2"
L1, L2 Case drain port 1 1/16-12UN-2B
L3, L4 Case drain port 1 1/16-12UN-2B
X1, X2 Pilot pressure port 7/16-20UNF-2B

6-9
· MAIN PUMP (1/2, STEERING)
10
24

27
23

6,31

37

2 16
12
51
53
33 52
1-2
54

30 1-1

7
17
22

15
20
25 76096WE11

1 Rotary group 12 Adjustment shim 27 Socket screw

1-1 High speed rotary group 15 Taper roller bearing 30 Locking screw
1-2 Control plate 16 Taper roller bearing 31 Double break-off pin
2 Adjusting piece 17 Bearing liner 33 Cylinder pin
5 Pump housing 20 Shaft seal ring 37 Side mark ring
6 Port plate 22 O-ring 51 Control valve
7 Swash plate 23 O-ring 52 Gasket
8 Drive shaft 24 O-ring 53 Socket head screw
10 Splined hub 25 Retaining ring 54 Locking screw

6-10
· MAIN PUMP (2/2, LOADER)

28

27
23

6,31
2
2

41
11
43 16
33 42 12

44 1-2

1-1
30

7
17
22

8
15
20
25
76096WE12

1 Rotary group 12 Adjustment shim 28 Locking screw

1-1 High speed rotary group 15 Taper roller bearing 30 Locking screw
1-2 Control plate 16 Taper roller bearing 31 Double break-off pin
2 Adjusting piece 17 Bearing liner 33 Cylinder pin
5 Pump housing 20 Shaft seal ring 41 Control valve
6 Port plate 22 O-ring 42 Gasket
7 Swash plate 23 O-ring 43 Socket screw
8 Drive shaft 25 Retaining ring 44 Locking screw
11 Adjustment shim 27 Socket screw

6-11
2) FUNCTION

1 2 3 4 5 6

LS pressure

12 13
X

11

8 9 10 L B

X L1 S

13 12 4 10
75796WE33

1 Drive shaft 6 Counter spring 11 Control plate

2 Swash plate 7 Pressure & flow compensator valve 12 Pressure compensator spool
3 Shoe plate 8 Piston shoe 13 Flow compensator spool
4 Counter piston 9 Cylinder
5 Piston 10 Control piston

The steering pump and loader pump are variable displacement piston pump. The steering pump
and loader pump are flow controlled by LS signal. When the steering and loader are not being
used, the pumps are at low pressure standby.
The load sensing pressure that is sensed from steering and loader hydraulic systems flows to flow
compensator spool (13). This spool keeps the pump output at a level that is necessary to fulfill the
requirements for the system flow and for the pressure.
The pressure compensator spool (12) also limits maximum system pressure. The pressure
compensator spool (12) prevents damage to the steering and loader hydraulic components from
excessive pressure.
The swivel angle of the pumps is controlled by counter piston (4) and control piston (10). Counter
spring (6) cause swash plate (2) to move at maximum displacement or causes swash plate (2) to
upstroke.
Control piston (10) has a larger area (diameter) than counter piston (4). Control piston (10) causes
swash plate (2) to destroke the pump.
Flow compensator spool (13) and/or pressure compensator spool (12) changes pump output by
regulating the pump discharge pressure that is acting on control piston (10).

6-12
Control piston (10) diameter is larger than counter piston (4) diameter, the oil pressure that is
acting against control piston (10) overcomes the force of counter spring (6). The oil pressure than
causes the pump to destoke.
Pressure and flow compensator valve (7) also controls the maximum output of pump pressure.
When steering and loader pressure rises above pressure compensator setting, pressure
compensator spool (12) overrides flow compensator spool (13). This causes the pump to destroke.

6-13
(1) Upstroking
14
1 2 4 6

15

LS pressure

12 13
X

21

22
10 L B

16

LS pressure oil
System pressure oil
Return oil L1 S
4 10
17 18 19 20 13 23 12
75796WE35

1 Drive shaft 13 Flow compensator spool 19 LS line from the metering pump
2 Swash plate 14 Case drain 20 Cavity
4 Counter piston 15 Passage 21 Passage
6 Counter spring 16 Passage 22 Passage
10 Control piston 17 Spring 23 Cavity
12 Pressure compensator spool 18 Spring

Upstroking of the pump occurs as flow demand from loader and steering system.
The increased flow demand causes a LS pressure in LS line (19). The LS pressure in LS line (19)
combines with the force of spring (18) in cavity (20).
The force of spring (18) causes pump pressure to be higher than the LS pressure (19).
If the combination of LS pressure and of spring force is greater than the pump discharge pressure,
this difference pressure causes spool (13) to move right. As spool (13) moves right, the spool (13)
blocks the flow of supply oil to control piston (10). Pump swash plate (2) is controlled by pressure
and flow as much as hydraulic system requests.
When the oil flow to control piston (10) is blocked, the pilot oil in passage (22) drains to passage
(23). The oil then flows past pressure compensator spool (12) and through passage (16) into the
housing and via the drain line (14) to tank.
Supply oil flows through passage (15) to counter piston (4). The oil acts against counter piston (4).
The oil combines with the force of counter spring (6). This causes swash plate (2) to upstroke.
This also causes the pump flow to increase. As flow requirements are satisfied, the pump output
pressure increase. The pressure increases until the pressure in passage (15) moves flow
compensator spool (13) up to be satisfied with system requirement for pressure and flow.
·Pump discharge pressure = force of spring (18) + LS pressure (19)

6-14
(2) Destroking

14
1 2 4 6

15

LS pressure

12 13
X

21

22
10 L B

16

LS pressure oil
System pressure oil
Return oil L1 S
4 10
17 18 19 20 13 23 12
75796WE34

1 Drive shaft 13 Flow compensator spool 19 LS line from the metering pump
2 Swash plate 14 Case drain 20 Cavity
4 Counter piston 15 Passage 21 Passage
6 Counter spring 16 Passage 22 Passage
10 Control piston 17 Spring 23 Cavity
12 Pressure compensator spool 18 Spring

The decreased flow demand causes a LS pressure in line (19). The LS pressure in line (19)
combines with the force of spring (18) in cavity (20).
This combination of LS pressure and of spring force is less than the pump pressure in passage
(21). This causes flow compensator spool (13) to move left.
Pump oil now flows through passage (15). The oil then flows past flow compensator spool (13),
through passage (22), and then to control piston (10).
The pump pressure behind control piston (10) is now greater than the combined force of counter
piston(4) and of counter spring (6). The angle of swash plate (2) decreases.
This decreases the pump output and the system pressure.
When the lower flow requirements are met, flow compensator spool (13) moves right up to the
balanced position. Swash plate (2) maintains an angle that is sufficient to provide the lower
required pressure. If the operator does not turn the steering wheel and does not move RCV, then
the pump will return to low pressure standby.
※ Control piston → Changes pump displacement ; influenced by controller.
Counter piston → Helps to change pump displacement but no possible to control this piston.

6-15
(3) Low pressure standby

14
1 2 4 6

15

LS pressure

12 13
X

21

22 L
10 24 B

16

LS pressure oil
System pressure oil
Return oil L1 S
4 10
17 18 19 20 23 13 12
75796WE36

1 Drive shaft 13 Flow compensator spool 19 LS line from the metering pump
2 Swash plate 14 Case drain 20 Cavity
4 Counter piston 15 Passage 21 Passage
6 Counter spring 16 Passage 22 Passage
10 Control piston 17 Spring 23 Cavity
12 Pressure compensator spool 18 Spring 24 Cross-drilled hole

Low pressure standby constitutes the following condition: a running engine and inactive steering
and loader. There are no flow demands on the pump or pressure demands on the pump.
Therefore, there is no LS pressure in line (19).
Before you start the engine, counter spring (6) holds swash plate (2) at the maximum angle. As the
pump begins to turn, oil begins to flow and pressure increases in the system.
Because of close centered steering control valve and close centered loader hydraulic system.
As this pressure increase, the pressure pushes flow compensator spool (13) against spring (18).
This causes flow compensator spool (13) to move left. This opens passage (23) in order to allow
pressure oil to flow to control piston (10).
The oil acts against control piston (10) in order to overcome the force of counter spring (6). The oil
causes control piston (10) to move to the left.
When control piston (10) moves to the left, the piston moves swash plate (2) toward the minimum
angle. Control piston (10) continues to move to the left until cross-drilled hole (24) allows the oil to
drain to the case.

6-16
 Cross-drilled hole (24) limits the maximum travel of control piston (10) to the left. The pump
supplies a sufficient amount of flow that compensates for system leakage. The pump also supplies
a sufficient of flow that compensates for leakage to the pump case. The leakage to the pump case
is a result of the cross-drilled hole. The pump maintains low pressure standby. Low pressure
standby pressure should not exceed 40 bar (580 psi).
※ Low pressure standby will vary in the same pump as the system leakage or the pump leakage
increases. The pump will upstroke slightly in order to compensate for the increasing leakage.
Control piston (10) will cover more of the cross-drilled hole.

6-17
(4) High pressure stall

14
1 2 4 6

15

LS pressure

12 13
X

21

22 L
10 24 B

16

LS pressure oil
System pressure oil
Return oil L1 S
4 10
17 18 19 20 23 13 12
75796WE36

1 Drive shaft 13 Flow compensator spool 19 LS line from the metering pump
2 Swash plate 14 Case drain 20 Cavity
4 Counter piston 15 Passage 21 Passage
6 Counter spring 16 Passage 22 Passage
10 Control piston 17 Spring 23 Cavity
12 Pressure compensator spool 18 Spring

When the hydraulic system stalls under load or when the cylinders reach the end of the stroke, the
main system pressure increases. But LS pressure (19) is regulated by LS relief valve on steering
system and loader system. The pressure difference between discharged pump and LS pressure
equal to spring (18). It means no flow is necessary. Therefore, discharged pressure push flow
compensator spool (13) left . Supply oil now flows past flow compensator spool (13) and through
passage (23). The oil flows past flow compensator spool (13) and into passage (22). The oil then
flows to control piston (10).
Pump swash plate (2) will be minimum displacement if the operator does not turn the steering
wheel and RCV, then the pump will return to low pressure standby.

6-18
(5) Adjustment of flow control
Flow compensator setting must be carried out following procedures and conditions.
① Conditions
- Engine is running (at high or low idle).
- RCV is operated slowly (example : Boom up).
- Pressure gauges are installed.
※ Discharge pump flow should be less than max pump flow.

② Procedures
- Loosening the hexagon nut (2).
- Adjusting screw (1) of flow controller by tightening or loosing the screw (1).
·Flow setting : ΔP = Gauge A - Gauge B
·Specification : Steering pump (25 bar) / Loader pump (20 bar)

Flow compensator Gauge B

X
2 1
Gauge A
-16 bar/rev
+16 bar/rev B

S L1 L
75796WE37

(6) Adjustment of pressure control

Pressure compensator setting must be carried out following procedures and conditions.
① Conditions
- Engine is running.
- System is at relief condition.

② Procedures
- Loosening the hexagon nut (2).
- Adjusting screw (1) of pressure controller by tightening or loosing the screw (1).
·Maximum pressure setting = Gauge A
·Specification : Steering pump (250 bar) / Loader pump (300 bar)
Pressure compensator
X

Gauge A

-52 bar/rev
+52 bar/rev

S L1 L
2 1 75796WE38

6-19
4. REMOTE CONTROL VALVE
1) STRUCTURE

4,3,1
4 1
10 3 2 12
30
11

2
33 30

4,3,1 14 32
40
15
40
4 1 42
20 3 2

22
21
23 4 1

3 2
25

26

45

7707WE11

1 Handle 14 Shim set 26 Bushing kit

3 Lever kit 15 Joint 30 Plunger kit
4 Bellows 20 Flange 32 Regulating unit
5 Nut 21 Solenoid complete 33 Regulating unit
10 Bracket 22 Plunger kit 40 Spring set
11 Detent kit 23 Plunger guide 42 Prefeel point kit
12 Plunger kit 25 Electric bracket 45 Plug set

6-20
2) OPERATION

T P

B.D/F B.U IN OUT

1 34 2
HYDRAULIC CIRCUIT
(3 Electromagnetic locks)

Electromagnetic lock 9

10

11 5

4
12
(1) Hydraulic functional principle 3
Pilot devices with end position locks operate as
7 2
direct operated pressure reducing valves.
They basically comprise of control lever (1), four T 8
x
pressure reducing valves, housing (6) and locks. P

Each pressure reducing valve comprises of a

control spool (2), a control spring (3), a return 6
spring (4) a plunger (5).
At rest, control lever (1) is held in its neutral position Port 4 Port 2
by return springs (4). Ports (1, 2, 3, 4) are 7707WE12

connected to tank port T via drilling (8).

When control lever (1) is deflected, plunger (5) is pressed against return spring (4) and control
spring (3).
Control spring (3) initially moves control spool (2) downwards and closes the connection between
the relevant port and tank port T. At the same time the relevant port is connected to port P via
drilling (8). The control phase starts as soon as control spool (2) finds its balance between the
force from control spring (3) and the force, which results from the hydraulic pressure in the
relevant port (ports 1, 2, 3 or 4).
Due to the interaction between control spool (2) and control spring (3) the pressure in the relevant
port is proportional to the stroke of plunger (5) and hence to the position of control lever (1).
This pressure control which is dependent on the position of the control lever and the
characteristics of the control spring permits the proportional hydraulic control of the main
directional valves and high response valves for hydraulic pumps.
A rubber bellows (9) protects the mechanical components in the housing from contamination.

6-21
(2) End position lock
Only those control ports, for which it is necessary to hold the control lever in a deflected position
are equipped with end position locks.
Electromagnetic lock
An additional spring (7), which is fitted below an additional plate (12) warns, by means of an
increased force, which is required for compressing this spring, that the plunger (5) and the control
lever (1) have almost reached their end position.
When this threshold is overcome, a ring (10) contacts the solenoid armature (11) ; if the solenoid
is energized, then control lever (1) is held in its end position by magnetic force.
This lock is released automatically when the solenoid is deenergized.

6-22
5. MAIN CONTROL VALVE
1) STRUCTURE (1/3)
·Type : Closed center, Load pressure - Independent - Flow - Distribution

a3 b3
A3 B3
LS
pst
a2 b2
A2 B2

a1 b1
A1 B1
P

a2 a3
LS

T P a1 A1 B1 A2 B2 pst A3 B3
Down Floating
Dump
Roll back

Bucket Boom Aux

Up

S1

S2
b1 A2 B2

b2 b3

Hydraulic circuit

76096WE10

Port Port name Port size

P From main pump SAE 1"
T To hydraulic tank SAE 1 1/4"
A1, B1 To bucket cylinder port SAE 3/4"
A2, B2 To boom cylinder port SAE 3/4"
a1, b1 Bucket pilot port 11/16-16UN
a2, b2 Boom pilot port 11/16-16UN
a3, b3 Auxiliary pilot port 11/16-16UN
LS Load sensing port 9/16-18UNF
Pst To RCV P port 9/16-18UNF
6-23
 STRUCTURE (2/3)

61

62

60

36 38
38
37
79

35
50

79
74
33
31

33 32
79

30

86
102 71

84
74

11
79
85
165
76096WE13

11 Housing 37 O-ring 74 Compensator valve

30 O-ring 38 O-ring 79 Pressure valve
31 O-ring 50 Housing 84 Flow regulator
32 O-ring 60 Plate 85 Precharge valve
33 O-ring 61 Cylinder screw 86 Pilot oil supply
35 O-ring 62 Washer 102 Locking screw
36 O-ring 71 Shuttle valve 165 Pressure relief valve

6-24
 STRUCTURE (3/3)

23
21
91
12
90 96
96
12 90 20
21 91
23 39

23
50 21
20
39 13

95
40 91 19
90
90 91
96 34 23
12
21
23
20
20
12
34
96
34 90
40
91
41 34

91
90 11
96

21
23

12

20

76096WE14

11 Housing 21 Throttle check valve 50 Housing

12 Cover 23 Threaded steel pipe fitting 90 Compression spring
13 Cover 34 O-ring 91 Spring retainer
14 Cover 39 O-ring 95 Spring retainer
19 Bolt 40 Spool 96 Spring retainer
20 Bolt 41 Spool

6-25
2) FUNCTION

4
6
A B

a T P b

A B
2 5 3 1 7

a2 3
LS

T P a1 A1 B1 A2 B2 pst
Down Floating
Dump
Roll back

Bucket Boom
Up

b1 A2 B2

4 6
b2

Hydraulic circuit

76096WE15

1 Housing 4 Counter balance valve 7 Spring chamber

2 Spool 5 Regeneration check valve
3 Pressure compensator 6 Port relief valve

6-26
(1) Control block
Proportional direction valve to the LUDV principle (Load pressure - Independent - Flow -
Distribution)
(2) Actuator control
At the spool (2) the direction and volume of flow is determined that flows to the actuator
connections (A or B).
The spring chambers (7) are supplied with pilot pressure either via the pilot connections a and b
hydraulic control.
The value of the pilot pressure within the spring chamber (7) determines the stroke of the spool
(2).
The pressure compensator (3) controls the pressure differential at the spool (2) and therefore, the
flow to the actuators (A, B).
(3)
3) Loader pressure compensation (LUDV)
The control block works to the LUDV principle. In this load - sensing version the pressure
compensators (3) are located between the spool (2) and the actuator connections (A, B).
The highest load pressure of all of the actuators involved is applied to all of the pressure
compensators. In parallel it is also applied to the pump.
If the pump flow is insufficient for all of the functions, then all work movements are reduced in
speed by the same ratio.
(4) Pressure safety, actuator connections
Large nominal size port relief valve (6) with combined anti-cavitation functions protect the
actuators from overloads and cavitation.
(5) Float position
The float position is obtained by means of a 4-position spool.
(6) Regeneration
(6
To prevent cavitation, with negative loads (e. g. dump or lowering), the tank port is pre-loaded via
counter balance valve (4) and is fed with oil via the regeneration check valve (5) downstream of
the pressure compensator.

6-27
3) BOOM SECTION OPERATION
(1) Spool in neutral

A2 B2

a2 T P b2

A2 B2

a2
LS

T P a1 A1 B1 A2 B2 pst
Down Floating
Dump
Roll back

Bucket Boom
Up

b1 A2 B2

b2

Hydraulic circuit
76096WE51

When the boom spool is in neutral position, oil from the pump will be blocked.
Then, the pumps are at low pressure stand by.

6-28
(2) Boom raise position

A2 B2

a2 T P b2

A2 B2

a2
LS

T P a1 A1 B1 A2 B2 pst
Down Floating
Dump

Boom
Roll back

Bucket
Up

b1 A2 B2

b2

Hydraulic circuit
76096WE52

When the pilot pressure is led to the port b2, the boom spool moved to raise position.
Oil from the pump flows to the cylinder port B2 and oil from the cylinder flows into the tank
passage through the cylinder port A2.

6-29
(3) Boom lower position

A2 B2

a2 T P b2

A2 B2

a2
LS

T P a1 A1 B1 A2 B2 pst
Down
Dump

Boom
Roll back

Bucket 6
Up

b1 A2 B2

b2

Hydraulic circuit
76096WE53

When the pilot pressure is led to the port a2, the boom spool moved to lower position.
Oil from the pump flows to the cylinder port A2 and oil from the cylinder flows into the tank
passage through the cylinder port B2.
When the lowering speed of boom is faster, the return oil from the large chamber of boom
cylinder combines with the oil from the pump through regeneration check valve (6), and flows into
the small chamber of the cylinder. This prevents cylinder cavitation by the negative pressure when
the pump flow cannot match the boom down speed.

6-30
(4) Boom float position

A2 B2

a2 T P b2

A2 B2

a2
LS

T P a1 A1 B1 A2 B2 pst
Dump

Floating

Boom
Roll back

Bucket
Up

b1 A2 B2

b2

Hydraulic circuit
76096WE54

When the boom spool is located in float position, the oil from the pump will be blocked.
The cylinder ports (A2, B2) are connected to the tank passage, so the boom will be lowered due
to it's own weight.

6-31
4) BUCKET SECTION OPERATION
(1) Spool in neutral

A1 B1

T P b1
a1

a2
LS

T P a1 A1 B1 A2 B2 pst
Down Floating
Dump
Roll back

Bucket Boom
Up

b1 A2 B2

b2

Hydraulic circuit
76096WE55

When the bucket spool is in neutral position, oil from the pump will be blocked.
Then, the pumps are at low pressure standby.

6-32
(2) Bucket rollback position

A1 B1

a1 T P b1

a2
LS

T P a1 A1 B1 A2 B2 pst
Down Floating
Dump

Roll back

Bucket
Boom
Up

b1 A2 B2

b2

Hydraulic circuit
76096WE56

When the pilot pressure is led to the port b1, the bucket spool moved to rollback position.
Oil from the pump flows to the cylinder port B1 and oil from the cylinder flows into the tank
passage through the cylinder port A1.

6-33
(3) Bucket dump

A1 B1

T P b1
a1

6 a2
LS

T P a1 A1 B1 A2 B2 pst
Down Floating
Dump

Bucket
Roll back

Boom
Up

b1 A2 B2

6
b2

Hydraulic circuit
76096WE57

When the pilot pressure is led to the port a1, the bucket spool moved to dump position.
Oil from the pump flows to the cylinder port A1 and oil from the cylinder flows into the tank
passage through the cylinder port B1.
When the dumping speed of bucket is faster, the return oil from the large chamber of bucket
cylinder combines with the oil from the pump through regeneration check valve (6), and flows into
the small chamber of the cylinder. This prevents cylinder cavitation by the negative pressure when
the pump flow cannot match the bucket dump speed.

6-34
6. SAFETY VALVE
1) STRUCTURE
2
4

5
P1

T
A1
A1

3 2
1

P1 T
Hydraulic circuit

Port Port name Port size

P1 From MCU PF 3/8"
A1 Supply to RCV lever PF 1/4"
T To hydraulic tank PF 1/4"
75796WE16

1 Bowl and element assy 4 Solenoid valve

2 Check valve 5 Accumulator
3 Cartridge

2) OPERATION
This valve is used to cut off the pilot circuit.
When the pilot cut off switch in the cab is pressed to ON position, the solenoid valve is activated
and then the pilot oil flow into the pilot circuit.
The accumulator satisfied short term peak power demands and is a source of emergency power in
case of main circuit pressure failures.

6-35
7. BOOM AND BUCKET CYLINDER
The boom cylinders are two unit and the bucket cylinder is one unit. They use a bolt on rod guide.
The piston (14) threads on to the rod (2) and is retained by a nut (20) and set screw (21).
The piston seals against the tube (1) with piston seal (15). Two wear rings (16) are located on each
side of the piston seal.
The gland (3, the rod guide) seals against the tube with an O-ring (12). The cylinder thread seals
against the rod with a lip type buffer ring (8) and a rod seal (6). A dust wiper (9) cleans the rod when
it is retracted.
1) BOOM CYLINDER

9,10 6,7 3 8 11 12,13 4 26 1 2 27 14 17 16 15 18,19 20 21 29

28

22 25 23,24

76096WE17

1 Tube assembly 11 O-ring 21 Set screw

2 Rod assembly 12 O-ring 22 Socket bolt
3 Gland 13 Back up ring 23 Pin bushing
4 Bushing 14 Piston 24 Dust seal
5 Snap ring 15 Piston seal 25 Band assy
6 Rod seal 16 Wear ring 26 Pipe assembly
7 Back up ring 17 Dust ring 27 Pipe assembly
8 Buffer ring 18 O-ring 28 O-ring
9 Dust wiper 19 Back up ring 29 Socket bolt
10 Snap ring 20 Lock nut

6-36
2) BUCKET CYLINDER

9,10 6,7 3 8 11 12,13 4,5 25 1 2 14 17 16 15 18,19 21 20

22 26 27 28 29 23,24

76096WE19

1 Tube assembly 10 Snap ring 19 Band assembly

2 Rod assembly 11 O-ring 20 Pipe assembly
3 Gland 12 O-ring 21 Pipe assembly
4 Bushing 13 Back up ring 22 Bolt
5 Snap ring 14 Piston 23 O-ring
6 Rod seal 15 Piston seal 24 Bushing
7 Back up ring 16 Wear ring 25 Dust seal
8 Buffer ring 17 Dust ring
9 Dust wiper 18 Bolt

6-37
8. HYDRAULIC OIL TANK
1) STRUCTURE
· The oil from the hydraulic tank is sent from the pump through main control valve to the cylinders.
In the return circuit, the oil from various parts merges.
· A part of oil is cooled in the oil cooler, passes through the hydraulic filter and returns to the
hydraulic tank (1).
· If the hydraulic return oil filter becomes clogged, return filter bypass valve (6) acts to allow the oil
to return directly to the hydraulic tank (1). This prevents damage to the hydraulic filter (5). The
bypass valve (6) is also actuated when negative pressure is generated in the circuit.

4 9 13 11,12

A B

7
1
A B
14
3 SECTION A - A

15

6
5
SECTION B - B

10 2,8

76096WE21

1 Hydraulic tank wa 9 Socket bolt

2 Pipe wa 10 Bolt
3 Sight gauge 11 Cover
4 Air breather 12 O-ring
5 Element assembly 13 Bolt
6 Bypass valve 14 Strainer
7 Spring 15 Spring
8 O-ring

6-38
2) RETURN OIL FILTER BYPASS VALVE
(1) When the filter is clogged
Bypass valve (1) is opened and the oil
1
returns directly to the tank without
passing through the filter.
·Bypass valve set pressure : 1.36 kg/cm2
(19.3 psi)

From MCV
770-3ATM (6-33)

6-39
3) AIR BREATHER
The air breather is equipped with the
capacity to perform three functions
simultaneously-as an air filter, breathing
valve, and as a lubrication opening.
(1) Preventing negative pressure inside the Air breather
tank
The tank is a pressurized sealed type, so
negative pressure is formed inside the
hydraulic tank when the oil level drops
during operations. When this happens,
the difference in pressure between the
tank and the outside atmospheric
pressure opens the poppet in the
breather, and air from the outside is let
into the tank or prevent negative pressure.
(2) Preventing excessive pressure inside
the tank
When the hydraulic cylinder is being
used, the oil level in the hydraulic system
increases and as temperature rises. If
the hydraulic pressure rises above the set
pressure, breather is actuated to release
the hydraulic pressure inside the tank. 75796WE22

6-40
9. ACCUMULATOR
The accumulator is installed at the safety
valve. When the boom is left the raised
position, and the control levers are operated
with the engine stopped the pressure of the
compressed nitrogen gas inside the
accumulator sends pilot pressure to the
control valve to actuate it and allow the boom
1
and bucket to come down under their own 2
weight.
3
Type of gas Nitrogen gas (N2)
Volume of gas 0.75ℓ(0.2 U.S.gal)
Charging pressure of gas 16 kg/cm2 (228 psi)
Max actuating pressure 128 kg/m2 (1820 psi)
1 Diaphragm
2 Steel pressure vessel
3 Closure button
7803AWE56

6-41