control valves in process control

1. CONTROL VALVES,
PRESSURE REGULATORS,
SOLENOID VALVES

2. WHAT IS A CONTROL VALVE?
 A CONTROL VALVE IS A FINAL CONTROL
ELEMENT IN A PROCESS CONTROL LOOP
TYPICALLY USED TO MANIPULATE FLOW
OF MATERIAL WITH AN OBJECTIVE TO
ATTAIN A DESIRED VALUE OF THE
CONTROLLED PROCESS VARIABLE. THIS
IS ACHIEVED BY THROTTLING FLOW OF
MATERIAL BY OPERATING A CLOSURE
MEMBER WHICH CLOSES THE VALVE’S
PORT, PARTIALLY OR FULLY.

3. CONTROL VALVE SIZING
 CONTROL VALVE SIZING IS THE PROCESS
OF DETERMINATION OF REQUIRED FLOW
CAPACITY OF A VALVE FOR A GIVEN
SERVICE

4. TYPES OF CONTROL VALVES
 CONTROL VALVES MAY BE CLASSIFIED
INTO DIFFERENT TYPES BASED UPON :
1. TYPE OF CONTROL ACTION
2. TYPE OF FLOW CHARACTERISICS
3. TYPE OF CONSTRUCTION
4. TYPE OF MOVEMENT

5. TYPES OF CONTROL VALVE
BASED UPON CONTROL ACTION
 A CONTROL VALVE WHOSE CLOSURE
MEMBER CAN BE DRIVEN TO ANY
POSITION BETWEEN FULL CLOSED AND
FULL OPEN POSITION IN RESPONSE TO
AN ANALOG SIGNAL AND USED FOR
MODULATING CONTROL ACTION IS
CALLED A MODULATING CONTROL VALVE.
 A CONTROL VALVE WHICH IS USED IN
EITHER FULL CLOSE OR FULL OPEN
POSITION FOR ON/OFF CONTROL IS
CALLED AN ON/OFF CONTROL VALVE.

6. TYPES OF CONTROL VALVE
BASED UPON FLOW CHAR
 FLOW CHARACTERISTIC OF A VALVE
REFERS TO THE MANNER IN WHICH
FLOW THROUGH A VALVE VARIES WITH
OPENING OF THE VALVE FROM FULL
CLOSE TO FULL OPEN POSITION. THE
DIFFERENT CHARACTERISTICS ARE:
1. LINEAR
2. MODIFIED LINEAR
3. EQUAL PERCENTAGE
4. QUICK OPENING

7. TYPES OF CONTROL VALVE
BASED UPON FLOW CHAR
 THE INSTALLED CHARACTERISTIC OF A
VALVE IS DIFFERENT FROM ITS INHERENT
FLOW CHARACTERISTIC.
 THE FLOW CHARACTERISTIC OF A
CONTROL VALVE IS DETERMINED BY ITS
TRIM(SEAT AND PLUG OR EQUIVALENT
PARTS).
 SOMETIMES A DESIRED FLOW
CHARACTERISTIC IS ALSO OBTAINED BY
SUITABLY ADJUSTING/REPLACING
POSITIONER PARTS, USUALLY A CAM.

8. TYPES OF CONTROL VALVE
BASED UPON FLOW CHAR
 THE FLOW CHARACTERISTIC WHEN A
CONTROL VALVE IS SUBJECTED TO A
FIXED PRESSURE DROP ACROSS IT IS
CALLED ITS INHERENT FLOW
CHACTERISTIC.
 THE FLOW CHARACTERISTIC WHEN A
CONTROL VALVE IS SUBJECTED TO A
VARYING PRESSURE DROP IN ACTUAL
PROCESS CONDITIONS WHEN INSTALLED
IS CALLED ITS INSTALLED FLOW
CHARACTERISTIC.

10. CONTROL VALVES - INHERENT
FLOW CHARACTERISTICS

11. TYPES OF CONTROL VALVE
BASED UPON CONSTRUCTION
 VALVES ARE CLASSIFIED BASED UPON CONSTRUCTION/DESIGN OF BODY/TRIM.
 THE COMMON TYPES ARE:
1. GLOBE-TOP-GUIDED/BOTTOM GUIDED/TOP AND BOTTOM GUIDED
2. CAGE/CAGE GUIDED
3. BUTTERFLY
4. ECCENTRIC DISC/TRIPLE OFFSET
5. BALL
6. PLUG
7. GATE
8. DIAPHRAGM/SAUNDERS/PINCH
9. NEEDLE
10. KNIFE-EDGE GATE
11. SEGMENTED BALL VALVE(V-NOTCH BALL VALVE)
12. DIVERTING VALVE
13. MIXING VALVE
14. 3/2-WAY PLUG VALVE
15. DUAL PORTED VALVE
16. DESUPERHEATER/ATTEMPERATOR
17. PRESSURE REDUCING AND DESUPERHEATING (PRDS)
18. LOW Cv

12. TYPE OF CONTROL VALVE
DEPENDING UPON MOVEMENT
 CONTROL VALVES ARE ALSO CLASSIFIED
BASED UPON MOVEMENT OF CLOSURE
MEMBER:
1. SLIDING STEM
2. ROTARY

13. A TYPICAL CONTROL VALVE

15. CONTROL VALVE ACTUATORS
 CONTROL VALVES ARE USUALLY OPERATED IN
RESPONSE TO A CONTROL SIGNAL USING AN
ACTUATOR.FOLLOWING ARE COMMONLY USED
ACTUATORS:
1. SPRING-DIAPHRAGM/AIR OPERATED
2. PISTON-CYLINDER/SINGLE OR DOUBLE
ACTING/AIR OPERATED
3. ELECTRIC-SOLENOID OPERATED
4. ELECTRIC-MOTOR OPERATED
5. PNEUMATIC MOTOR OPERATED
6. HYDRAULIC
 SOME CONTROL VALVES MAY ALSO BE
OPERATED MANUALLY.

16. CONTROL VALVES
FAILSAFE POSITION
 CONTROL VALVES ARE ALWAYS DESIGNED TO
ATTAIN A SPECIFIED FAILSAFE POSITION IN
CASE OF ACTUATING POWER ----
(AIR/HYDRAULIC/ELECTRIC) FAILURE OR
CONTROL SIGNAL FAILURE.
 THE MOST COMMON FAILSAFE POSITIONS ARE
FULL CLOSE/FULL OPEN/HOLD(LAST).
 THIS IS USUALLY ACHIEVED BY USE OF SPRING-
RETURN ACTUATORS OR SPECIALLY DESIGNED
EMERGENCY BACKUP SYSTEM AND SUITABLE
ACCESSORIES.

17. CONTROL VALVE ACCESSORIES
 IN ADDITION TO THE ACTUATOR, A CONTROL VALVE IS USUALLY
PROVIDED WITH ONE OR MORE OF FOLLOWING ACCESSORIES:
1. POSITIONER-FOR POSITIONING A MODULATING CONTROL VALVE
2. SOLENOID VALVE-FOR OPERATION OF AN ON/OFF VALVE OR
INTERLOCKING OPERATION OF A MODULATING VALVE.
3. LIMIT SWITCHES-FOR DETECTING SPECIFIC POSITIONS OF VALVE
4. AIR-FILTER REGULATOR-FOR FILTERED AND PRESSURE REGULATED AIR
SUPPLY
5. POSITION TRANSMITTER – FOR REMOTE INDICATION OF VALVE
POSITION
6. VOLUME BOOSTER – FOR FAST VALVE OPERATION BY PROVIDING AIR
IN VOLUMES HIGHER THAN A NORMAL POSITIONER
7. EMERGENCY BACKUP SYSTEM – THIS IS USUALLY PROVIDED FOR
ATTAINING FAILSAFE POSITION WITH SOME TYPE OF ACTUATORS.
SOMETIMES IT MAY ALSO PROVIDE FOR EMERGENCY VALVE
OPERATION.
8. I/P CONVERTER – FOR CONVERTING ELECTRIC CONTROL SIGNAL TO
PNEUMATIC CONTROL SIGNAL IN CASE OF A MODULATING CONTROL
VALVE.

18. CONTROL VALVE SELECTION
AND SPECIFICATION
 EVERY CONTROL VALVE IS SPECIFICALLY SELECTED FOR A GIVEN APPLICATION.PROPER
SELECTION IS CRUCIAL FOR ACHIEVING DESIRED PERFORMANCE. SELECTION IS BASED UPON
FOLLOWING CONSIDERATIONS:
1. SERVICE – FLUID,PHYSICAL AND CHEMICAL PROPERTIES OF FLUID AND OPERATING/NORMAL
AND EXTREME PROCESS CONDITIONS.
2. CONTROL ACTION – MODULATING OR ON/OFF
3. CONTROL OBJECTIVE – THE NATURE OF PROCESS PARAMETER TO BE CONTROLLED.
4. MATERIAL OF CONSTRUCTION – TO BE SELECTED FOR COMPATIBILITY WITH FLUID AND
SERVICE CONDITIONS TO WITHSTAND EFFECTS OF CORROSION/EROSION/STRESS
CRACKING/MATERIAL FAILURE.
5. END CONNECTIONS AND PHYSICAL DIMENSIONS.
6. SUITABILITY OF GIVEN VALVE DESIGN/CONSTRUCTION.
7. FLOW CAPACITY – CONTROL VALVE SIZING.
8. FLOW CHARACTERISTIC.
9. ALLOWABLE LEAKAGE IN FULL CLOSE POSITION.
10. RESTRICTIONS ON FUGITIVE EMISSIONS.
11. IDENTIFYING POTENTIAL FOR CAVITATION/CHOKED FLOW CONDITION/AERODYNAMIC NOISE
AND AVOIDING THE SAME.
12. FAILSAFE POSITION.
13. APPROPRIATE ACTUATOR TYPE AND SIZE.
14. REQUIRED ACCESSORIES.
15. APPLICABLE CODES,STANDARDS AND PRACTICES.
16. PRIOR PERFORMANCE DATA IN SAME/SIMILAR APPLICATIONS.
17. MANUFACTURER’S RECOMMENDATIONS.

19. CONTROL VALVE SIZING
 CONTROL VALVE SIZING IS A SYSTEMATIC PROCEDURE FOR DETERMINING
REQUIRED FLOW CAPACITY OF A VALVE FOR A GIVEN APPLICATION.
 FLOW CAPACITY OF A VALVE IS USUALLY EXPRESSED AS Cv (OR SOMETIMES Kv)
VALUE.
 Cv IS DEFINED AS THE AMOUNT OF WATER AT 60 DEG F IN USgpm FLOWING
THROUGH A FULL OPEN VALVE WHEN THE PRESSURE DROP ACROSS THE VALVE IS
ONE psi.
 APPROPRIATE VALVE IS SELECTED USING MANUFACTURER’S DATA WITH SELECTED
Cv MATCHING OR NEXT HIGHER THAN CALCULATED Cv.
 USUALLY VALVES ARE SIZED TO HAVE 75 TO 85% OPENING AT MAXIMUM FLOW
RATE.
 IT IS BEST TO SIZE A CONTROL VALVE WITH AN OBJECTIVE TO MEET DESIRED
PROCESS GAIN SPECIFICATION.
 USE OF APPROPRIATE SOFTWARE IS RECOMMENDED FOR VALVE SELECTION AND
SIZING. IN SPECIAL APPLICATIONS, USE MANUFACTURER’S RECOMMENDED SIZING
PROCEDURE.
 CALCULATIONS ARE ALSO MADE TO CHECK FOR AND AVOID CAVITATION, CHOKED
FLOW CONDITIONS AND AERODYNAMIC NOISE.
 SUITABLE ACTUATOR IS ALSO DETERMINED USING ACTUATOR SIZING PROCEDURE.

21. CONTROL VALVE SIZING
STANDARDS

22. CONTROL VALVE TESTING
 A CONTROL VALVE IS EXHAUSTIVELY TESTED AT
MANUFACTURING LOCATION WITH RESPECT TO
MOC,PRESSURE RATING, MATERIAL /
MANUFACTURING DEFECTS,ALLOWABLE
LEAKAGE AND AS PER MODERN TREND MAY BE
SUBJECTED TO STATIC AND DYNAMIC
PERFORMANCE TESTS TO EVALUATE/PREDICT
ITS LOOP PERFORMANCE WHEN INSTALLED.
 THE APPLICABLE TEST PROCEDURES AND
REQUIRED TEST CERTIFICATES ARE USUALLY
SPECIFIED DURING PROCUREMENT.
 IT IS RECOMMENDED TO TEST A CONTROL
VALVE WHENEVER IT IS OVERHAULED OR
REPAIRED.

23. PRESSURE REGULATING VALVES
 PRESSURE REGULATING VALVES OR PRESSURE
REGULATORS OR SELF-ACTUATED PRESSURE
CONTROL VALVES ARE SPECIALLY DESIGNED
VALVES WHICH USE THE ENERGY/PRESSURE OF
PROCESS FLUID TO OPERATE THEIR CLOSURE
MEMBER TO PARTIALLY OR FULLY CLOSE A PORT
TO MAINTAIN A SET PRESSURE-
DOWNSTREAM/UPSTREAM OR DIFFERENTIAL,
USUALLY ADJUSTED BY ADJUSTING A SCREW
USUALLY PROVIDED FOR THE PURPOSE.

24. PRESSURE REGULATING VALVES
 A PRESSURE REGULATING VALVE(PCV) MAY
CONTROL PRESSURE DOWNSTREAM OF
IT,UPSTREAM OF IT OR DIFFERENTIAL ACROSS
IT DEPENDING UPON APPLICATION.
 PCVS ARE USUALLY CLASSIFIED BASED UPON:
1. THE LOCATION OF PRESSURE IT CONTROLS IN
RELATION TO ITS INSTALLED LOCATION.
2. CONSTRUCTION/DESIGN

25. PCV TYPE BASED UPON
CONTROLLED PRESSURE
 DOWNSTREAM PCV
 UPSTREAM PCV OR BACKPRESSURE CV
 DIFFERENTIAL PCV

26. PCV TYPE BASED UPON
CONSTRUCTION/DESIGN
 DIRECT OPERATED PCV – HERE THE CLOSURE MEMBER IS
DIRECTLY OPERATED BY ACTUATING DIAPHRAGM BY
BALANCING FEEDBACK PRESSURE AGAINST SET
PRESSURE SPRING FORCE. THE FORCE REQUIRED TO
OPERATE THE CLOSURE MEMBER IS RELATIVELY LOW AND
PCV SIZE/FLOW CAPACITIES ARE ALSO NOT LARGE.
 PILOT OPERATED PCV – HERE THE CLOSURE MEMBER IS
OPERATED BY PRESSURE DELIVERED TO ACTUATING
DIAPHRAGM THROUGH A PILOT VALVE WHICH BALANCES
FEEDBACK PRESSURE AGAINST SET PRESSURE SPRING
FORCE. THIS CONSTRUCTION IS OFTEN USED WHERE
SIZE/FLOW CAPACITY REQUIREMENTS ARE HIGH AND THE
FORCE REQUIRED TO OPERATE THE CLOSURE MEMBER IS
RELATIVELY HIGH.

27. DIRECT OPERATED PCV

28. PILOT OPERATED PCV

29. PILOT OPERATED PCV

30. VACUUM REGULATOR

31. COMPONENTS OF A STRAIGHT
STEM DIRECT OPERATED PCV

32. COMPONENTS OF A LEVER
STYLE DIRECT OPERATED PCV

33. COMPONENTS OF A LOADING
STYLE PILOT OPERATED PCV

34. UNLOADING STYLE PILOT
OPERATED PCV

35. SELECTION OF PCV
A PCV IS SELECTED BASED UPON FOLLOWING CONSIDERATIONS:
 Service and application
 Maximum inlet and outlet pressures (operating and emergency)
 Adjustable pressure range
 Outlet pressure ranges
 Flow capacity
 End connection styles
 Regulator construction materials
 Accuracy
 Pressure registration (internal or external)
 Temperature capabilities
 After comparing the regulator capabilities of alternative models

36. SIZING OF PCV
 SIZING IS THE SYSTEMATIC PROCEDURE OF
DETERMINING FLOW CAPACITY OF A PCV FOR A
GIVEN APPLICATION. IT IS USUALLY EXPRESSED
AS Cv VALUE. REFER TO MANUFACTURER’S
HANDBOOK.
 IT IS IMPORTANT TO SIZE A PCV USING
REGULATED FLOW CAPACITY RATHER THAN
WIDE-OPEN FLOW CAPACITY;THE TWO ARE
DIFFERENT. THE WIDE-OPEN FLOW CAPACITY IS
GREATER THAN THE REGULATED FLOW
CAPACITY AND TYPICALLY APPLIES WHEN A PCV
FAILS OR IT IS USED WHEN SIZING VALVES FOR
PRESSURE RELIEF APPLICATIONS.

37. SOLENOID OPERATED VALVES
 A SOLENOID OPERATED VALVE(SOV) USES AN
ELECTRIC SOLENOID TO OPERATE A PLUNGER
TO SWITCH CONNECTIONS BETWEEN TWO OR
MORE PORTS CARRYING A PRESSURISED FLUID.
 PRIMARILY USED AS A CONTROL ACCESSORY TO
OPERATE ON/OFF VALVES,PNEUMATIC
ACTUATORS, HYDRAULIC ACTUATORS FOR
ON/OFF SERVICE OR INTERLOCKING CONTROL
VALVES TO FAIL SAFE POSITION.
 IN SOME APPLICATIONS SOVS ARE USED TO
DIRECTLY HANDLE PROCESS FLUID FOR ON/OFF
SERVICE.

38. SOLENOID VALVES

39. TYPES OF SOVS
 SOVS ARE USUALLY CLASSIFIED BASED UPON
TOTAL NUMBER OF PORT CONNECTIONS,TOTAL
NUMBER OF POSSIBLE SWITCHING STATES FOR
SWITCHING PORT CONNECTIONS AND METHOD
OF OPERATION-DIRECT OR PILOT OPERATED.
 SOVS ARE AVAILABLE FOR VARIOUS OPERATING
AC/DC VOLTAGES.
 EX-PROOF AND INTRINSICALLY SAFE VERSIONS
ARE AVAILABLE FOR USE IN HAZARDOUS AREAS.

40. TYPES OF SOVS
 PROPORTIONAL SOLENOID VALVES
 SOLENOID VALVES 2/2 PILOT OPERATED
 VALVES 2/2 PRESSURE OPERATED
 VALVES 3/2 PRESSURE OPERATED
 VALVES 4/2 AND 5/2 DIRECT / PILOT OPERATED
 EXPLOSIONPROOF SOLENOIDS
 SOLENOID VALVES 3/2 PILOT OPERATED
 SOLENOID VALVES 3/2 DIRECT OPERATED
 SOLENOID VALVES 2/2 DIRECT OPERATED
 SPECIAL SERVICE VALVES
 Dust collector systems : 9/01 Hot water and steam: 9/05 Medical +
analytical : 9/09
 Engineering contractors : 9/02 Combustible gas (EN 161) and oil : 9/06
Magnetic latch : 9/10
 NAMUR based valves : 9/03 Cryogenic: 9/07 Spool valve islands : 9/11
 Fuel dispensing: 9/04 Vacuum service : 9/08

41. A TYPICAL SOV-3/2 WAY

42. A TYPICAL SOV-5/2WAY

45. SUGGESTED READING
 SELECTION AND SIZING OF CONTROL
VALVES – LES DRISKELL/ISA
 SELECTION OF CONTROL VALVES – ISA
 SIZING OF CONTROL VALVES – ISA
 CONTROL VALVE HANDBOOK – SKOUSEN
 CONTROL VALVE HANDBOOK – FISHER
CONTROLS
 REGULATOR HANDBOOK – FISHER
CONTROLS
 ASCO VALVE CATALOG

46. THANK YOU