The document discusses different types of adjustable pressure limiting valves used in hydraulic systems, including: - Pressure relief valves, which limit pressure buildup by diverting excess fluid to the reservoir. - Pilot-operated relief valves, which use a balanced piston or spool to block fluid passage until excess pressure causes it to slide and allow bypassing to the reservoir. - Sequence valves, which provide flow to a second consumer once the pressure at a first consumer reaches a threshold. - Counter-balance valves, which control cylinders to prevent free-falling and are commonly used in forklifts, loaders, and excavators. - Pressure-reducing valves, which maintain a reduced pressure in certain

1. Dr Nisar Ahmed Arain
Assistant Professor
Anesthesia/Critical Care/ER
ADJUSTABLE PRESSURE
LIMITING VALVE

2. -Contents
-Introduction
-Classification of Pressure
control valve
-Pressure relief valve
-Direct acting relief valve
-Pilot operated relief valve
-Sequence control valve
-Conclusion
-Reference

3. INTRODUCTIO
N
-Pressure development via restriction
control and check of the
developing
pressure thus pressure relief valve
is used.
-manipulation of pressure and flow of
oil in different circuits.

4. -Terms related to Pressure Valves
a. Cracking
Pressure
-The pressure at which the valve just
begins to bypass the pressurized
fluid
to reservoir is called Cracking-
Pressure.
-At this pressure the force developed
by
fluid at ball or poppet (which ever is
used) just over-come the
compressive
force of spring retaining ball or
poppet
on valve seat.

5. b. Full-flow Pressure
-As fluid start by-passing through the
valve, the poppet gets lifted from its seat.
This lifting of poppet cause compression
of the spring. As spring get
compressed its force on poppet
increases, Hence to further compress
spring and allow more passage to fluid for
free flows require more pressure.
-Hence for full-flow of fluid through relief
valve is at much high pressure than
cracking pressure.
-The pressure at which full-flow of pump
by-passes to reservoir is called
“Full-Flow Pressure”

6. -Types of Pressure Control Valves
There are six types
of
pressure-control
valves
-Pressure Relief valves
-Unloading valves
-Sequence valves
-Pressure-reducing
valves
-Counter-balance
valves
-Safety value

7. Pressure Relief Valve (PRV)
--A closed valve is to limit the pressure
into
prescribe maximum by diverting some
or
all output of pump to tank.
--The pressure can rise in a hydraulic
system if
1-The flow rate from the pump is larger
than the flow rate through the
actuator
2- The volume of a closed system is
reduced
3- The hydraulic resistance of the
system
rises
4- The pressure relief value are

8. Construction
-It consists of a valve body, poppet, spring and adjusting
screw
-Poppet held on valve seat by spring compression, which is
adjusted by screw.

10. -
WORKIN
G

11. -Pilot Operated Relief Valve
-In case of direct acting relief valve the
pressurized fluid is stopped by spring
loaded
poppet against by-passing to the
reservoir
-While in case of pilot operated relief valve a
balanced piston or spool block the
passage
of pressurized fluid against bypassing to
reservoir.
-Excesspressure cause unbalances of the
piston, because of which it slides to one
side allowing pressurized fluid to by-
pass
to the reservoir.

12. -WORKING OF PILOT
OPERATED PRESSURE
RELIEF VALUE

14. -
Advantages
-Smaller package on larger pipe size
-More option for control
-Seals more tightly as system pressure
approaches but doesn’t reach the
set pressure.
-Control pilot can be mounted
remotely
-It can be used in engines

15. -
DISADVANTAG
ES
-More complex ,resulting in various
fail –open failure modes
-more expensive at smaller size
-Small parts in pilot values are
sensitive to contaminants
particles

16. SEQUENCE VALVE
-The function of sequence valve is to
provide flow to a second
consumer
in the case when the pressure
level
at a particular consumer has
reached
a threshold valve.
-As the name implies it is used for
sequencing the operation one
after
another.

17. Application
s
-Such application is mostly for in
“Tooling
and Automation” where several
operation are sequenced in pre
determined manner.
-A check valve is connected in parallel
with
sequence valve so that both
cylinder
will retract simultaneously
- ( no sequencing is desired in
retracting).

18. -Counter balance
valve
-Control the vertical cylinder
to not allow it to fall freely.
-Also known as back
pressure
valves.

19. -
APPLICATION
S
-Mainly Used in FORKLIFTS
when
heavy loads are to be
brought
down
- Also used in loaders and
JCB’S
for easy load pickup and
lowering of loads
-Hydrolic machines

20. -Pressure Reducing
Valve
-Open pressure control valves
used to maintain reduced
pressure in the required
portion
is done by increasing the area
where the oil could release the
pressure.

21. -APPLICATIONS
-Air Compressors
-Used in inlet of flow of load in
pressure
reactors.
-Aircrafts and Aerospace
-Cooking water pressure reduction
-Oxyfuel welding and cutting
- Propane/lpg gas industrial
transportation and storing
- Mining industries

22. Safety values
-All the pressure relief values
are kind of safety values.
-Safety values are values that
acts as a fail safe in a
thermal hydraulic plant.
-Safety value came to existence
as the early steam boilers
ware prone to explosion.

23. THANK YOU