Valves
Valves Uses
Stopping & starting flow
Regulating flow
Permitting flow in one direction
Switching flow
Emergency relief flow
General Valve Application
In general, block valves that are used to isolate equipment or process units
shall be of gate, ball or plug type.
Hand control valves shall be of globe type.
Gate valve should not be used in throttling service due to high erosion rate
of gate & seat
Butterfly valves should be used for cooling water service generally, 6 &
larger
Use of globe valves in sizes 3 and larger should be avoided due to high
cost
If valve is used for particular service and it is not shown in piping class,
then it is treated as piping speciality item.
Comparison of Basic Type of valves
Valve Type
Characteristics
Use
Limitations
Gate
Gate like disc actuated
by stem, screw & hand
wheel move at right
angle to flow
On-off service
Not good for
throttling service.
Throttling can
cause erosion.
Comparison of Basic Type of valves
Comparison of Basic Type of valves
Valve Type
Globe
A) Standard
B) Y Pattern
Characteristics
Use
Disc attached to stem Preferred for
seats on circular
throttling service.
opening. Fluid
changes direction in
passing through valve.
Y-type valve
produces lower
pressure drop &
turbulence than
std. globe &
preferred for
high P/T service
Limitations
Not recommended for
on-off service. Cost &
throttling efficiency
above 6 become
unfavorable. Not
recommended where
solids or corrosives are
present
Same as above
Comparison of Basic Type of valves
Comparison of Basic Type of valves
Comparison of Basic Type of valves
Valve Type
Characteristics
Use
Limitations
Butterfly
Valve
Circular disc is pivoted
at centre & opened by
turn of external
handle.
Where minimum
pressure drop &
face to face
dimensions is
required. May be
used for throttling
Positive shut-off is not
always possible except
when disc or seals are
coated with elastomers
which may limit max
allowable temperature
Comparison of Basic Type of valves
Comparison of Basic Type of valves
Valve Type
Angle (90)
Characteristics
Similar to globe valve
except inlet & out
make 90 angle
Use
Same as globe.
Used for high
pressure drop
service.
Limitations
Bends in piping system
are subject to strains
that should be placed
on valves.
Comparison of Basic Type of valves
Comparison of Basic Type of valves
Valve Type
Characteristics
Plug Valve
Tampered plug with
hole same shape as
interior of valve
body.
Use
Limitations
On-off service. More May be difficult to
positive shut-off than operate.
gate valve. Also used
for throttling but
characteristics not as
satisfactory as globe
for such service.
Comparison of Basic Type of valves
Comparison of Basic Type of valves
Valve Type
Characteristics
Use
Ball Valve
Related to plug valve
except movable
element is ball.
turn from full open
to full closed
Similar to plug valve.
Low pressure drop
across valve. Full port
valve reduces holdup of solids.
Limitations
Limited temp range
because of elastomer
seats. Gives tighter
shut-off than plug
Comparison of Basic Type of valves
Comparison of Basic Type of valves
Valve Type
Characteristics
Check valve
Use
Limitations
General: prevent back
flow in lines
a) Swing
check
Flow keeps swing
gate open while
reverse flow close
it.
Best for liquids & less
affected by solids in
fluid.
Not suitable for pulsating
flow. Some style operate
only in horizontal
position.
b) Dual
flapper
check
Dual flapper
Lower pressure drop
than swing check
Not suitable for pulsating
flow.
a) Piston
check
Flow pattern as
globe valve
Good for vapor,
Design for horizontal
steam, water. Suitable service. Not
for pulsating flow
recommended over 6
line size & service where
solids
Comparison of Basic Type of valves
Valve Type
d) Ball
check
Characteristics
Use
Stops flow reversal more
rapidly than others. Good
for viscous fluids. Vertical
& horizontal installation is
possible
Limitations
Not common over size 6
not suitable for pulsating
flow can act as flow
limiting device.
Comparison of Basic Type of valves
Comparison of Basic Type of valves
Valve Type
Automatic
Control
Characteristics
Similar in principle to globe
valve but precision built for
accurate automatic control.
Air pressure actuates the
diaphragm causing stem to
move, opening or closing
valve orifice. Double port
valve gives better control
range & require only small
force to move stem.
Use
Limitations
First cost is high. Double
port valves are very
good for tight shut-off.
Control valves which
normally throttle are
subject to wear and are
normally not preferred
for emergency shut-off
purposes. Control valves
often have bypass or
hand wheel. Control
valves require tight shutoff (TSO) or bubble tight
shut-off (BTSO) must be
indicated in P&ID.
Comparison of Basic Type of valves
Valve Type
Characteristics
Self-regulating
automatic
control
Sensing element &
control valve in
single unit
Use
When local control
is satisfactory as
fixed pressure
reduction stations
Limitations
Require local
readjustment for any
required changes in
downstream flow or
pressure conditions
Comparison of Basic Type of valves
Valve Type
Characteristics
Packless
Diaphragm seal the
Diaphragm valve bonnet, seating member
may be separate disc
diaphragm or solid
diaphragm
Use
For corrosive,
volatile , toxic
fluids service
where leakage
cannot be
tolerated
Limitations
Diaphragm may be
rubber like or plastic
material which
cannot withstand
temp above 40 C
Cannot considered as
fire safe due to use
of elastomers
Comparison of Basic Type of valves
Valve Type
Relief valve
Characteristics
Valve opens automatically
when force on seat exceeds
that of spring. Return to
closed position when
pressure drops below set
pressure
Use
Limitations
For protecting
Require periodic
equipment from inspection to insure
overpressure
operability
Valve Arrangements Around Pumps
Gate valves on suction &
discharge for isolation
Check valve to avoid back
flow
Check valve location:
upstream of discharge block
valve & close to pump
nozzle
Exchanger Valving
Upper detail is cheaper,
however it requires
complete shutdown of
cooling system
Lower detail is preferred by
most of clients as it allows
service users without
complete shutdown of
drainage of cooling system
Valve Around Flow meter
Globe valve in bypass to
maintain proper throttling &
regulation
Downstream valve shall be
either globe or needle valve
if needle valve is integral
with rotameter then
downstream valve should
be gate valve.
MOC Changes
