1. PRESSURE CONTROL VALVES (PCVs)
To be delivered by
MUHAMMAD ARIF NASIM
E & I (Instrument)
Apprentice Engineer, 13th Batch
July 09, 2008

2. WHAT IS A PCV Matches the flow of a fluid.
Maintains the system Pressure within acceptable limits.

3. BENEFITS OF PCV OVER CONTROL VALVE
PCVs are simpler devices than control valves.
PCVs are self operated control devices.
PCV requires energy from the controlled system to operate whereas control valve requires external power sources and control instruments.

5. SELF-OPERATED PCVs Also called Direct-operated PCVs
Used for low flow rates.
Simpler in construction.
Three components
Restricting element
Loading element
Measuring element

6. 1. RESTRICTING ELEMENT Restricts/regulates the flow of a fluid.
Usually a PLUG that can be positioned fully open, fully closed, or in throttling mode.
Restricting
Element

7. 2. LOADING ELEMENT Provides force and moves the restricting element.
Connects directly with restricting element.
Usually a SPRING or WEIGHT.
Loading Element

8. 3. MEASURING ELEMENT Senses the downstream pressure.
Connects directly with loading element.
Usually a diaphragm that can sense the pressure and move accordingly.
Measuring
Element

9. EXAMPLE OF SELF-OPERATED PCV
Model No 95BH Self-operated PCV
Measuring
Element
(Diaphragm)
Restricting Element
(Plug)
Loading Element
(Spring)

10. WORKING PRINCIPLE OF PILOT-OPERATED PCVs
Basically a self-operated PCV along with a pilot.
Used for higher flow rates.
Fast response.
Four components
Restricting element
Loading element
Measuring element
Pilot }
These three components are same as for self-operated pcv

11. PILOT-OPERATED PCV
USE OF PILOT
TWO-PATH CONTROL METHOD

12. EXAMPLE OF PILOT-OPERATED PCV
Model No 92B Pilot-operated PCV

13. SELECTION CRITERIA OF A PCV
Outlet pressure to be maintained.
Inlet pressure to the regulator.
Capacity required.
Shutoff capability required.
Process fluid.
Process fluid temperature.
Pipe size required.
End connection style.
Material requirements.

14. OVERPRESSURE PROTECTION METHODS
RELIEF VALVES
SERIES REGULATOR
WIDE-OPEN MONITOR

15. RELIEF VALVES
Similar to Self-operated PCV except that it senses upstream pressure rather then downstream pressure.
Vents process fluid to atmosphere (Usually)

16. SERIES REGULATOR Two PCVs are connected in cascading (head to tail)
If any PCV fails, the downstream pressure will be maintained by the other PCV within safe maximum pressure.

17. WIDE-OPEN MONITOR
Under normal conditions Monitor is fully open and Worker is in regulating mode.
Both PCVs senses the same downstream pressure.
Monitor has slightly high Set Pressure than Worker.
Monitor Worker

18. APPLICATIONS OF PCV Air Steam Liquids Process gases Natural gas Water
etc

19. THE PCV DOES NOT MATCHES THE REQUIRED FLOW CAPACITY?
WHY DAP HGG PCV FAILED
Downstream Pressure was within range.
Inlet pressure was perfectly suitable for the selected PCV.
End connections were OK.
Process fluid matches with the specifications of PCV.
The pipe size were perfectly OK.
Overprotection was provided by means of slam-shut.
THE PCV DOES NOT MATCHES THE REQUIRED FLOW CAPACITY
WHAT IS REMAINING

20. QUESTIONS