Process Control Valves are used in industrial plants to regulate flow, pressure, temperature, and level within a process system.
These valves are commonly found in refineries, power plants, chemical industries, water treatment facilities, and manufacturing units. For instrumentation students and working engineers, a clear understanding of process control valves is important for exams, interviews, and day-to-day field work.
This article presents 100 objective questions and answers on Process Control Valves, organised in batches of ten, with short explanations to help build strong fundamentals and practical clarity.
Objective Questions on Process Control Valves (Q1–Q10)
Q1. What is the main purpose of process control valves in an industrial system?
a) Measure flow rate
b) Regulate process variables
c) Store process fluid
d) Generate compressed air
Correct Answer: b
Explanation: Process control valves regulate variables such as flow, pressure, temperature, and level by adjusting the flow passage according to the control signal.
Q2. Which process variable is most commonly controlled using control valves?
a) Density
b) Flow
c) Viscosity
d) Conductivity
Correct Answer: b
Explanation: Flow control is the most common application of process control valves in industrial plants.
Q3. Which signal is most widely used to control control valves in modern plants?
a) 0–5 V
b) 0–10 V
c) 4–20 mA
d) Pulse signal
Correct Answer: c
Explanation: A 4–20 mA signal is widely used due to its noise immunity and fault detection capability.
Q4. Which component converts an electrical signal into valve movement in process control valves?
a) Valve body
b) Actuator
c) Bonnet
d) Trim
Correct Answer: b
Explanation: The actuator converts the control signal (pneumatic, electric, or hydraulic) into mechanical motion to move the valve stem.
Q5. What does “fail-safe position” mean in control valves?
a) Valve remains in last position
b) Valve moves to a predefined safe position on failure
c) Valve opens fully at high pressure
d) Valve closes only during maintenance
Correct Answer: b
Explanation: In case of power or air failure, process control valves move to a predefined position to maintain process safety.
Q6. Which type of actuator is most commonly used with control valves?
a) Manual actuator
b) Electric actuator
c) Pneumatic actuator
d) Hydraulic actuator
Correct Answer: c
Explanation: Pneumatic actuators are widely used due to their simplicity, reliability, and suitability for hazardous areas.
Q7. What is the function of a valve positioner in control valves?
a) Increase flow rate
b) Control line pressure
c) Ensure accurate valve positioning
d) Reduce noise
Correct Answer: c
Explanation: A positioner ensures that the valve stem position accurately matches the control signal.
Q8. Which part of control valves directly throttles the flow?
a) Actuator
b) Bonnet
c) Valve trim
d) Yoke
Correct Answer: c
Explanation: The valve trim, including plug and seat, directly controls the amount of fluid passing through the valve.
Q9. Which control action causes the valve to close when the control signal increases?
a) Direct acting
b) Reverse acting
c) Fail-open
d) Fail-close
Correct Answer: b
Explanation: In reverse-acting process control valves, an increase in signal causes the valve to close.
Q10. Which parameter defines the flow capacity of control valves?
a) Valve size
b) Pressure rating
c) Cv value
d) Actuator type
Correct Answer: c
Explanation: Cv represents the flow coefficient and indicates the flow capacity of process control valves under specified conditions
Objective Questions on Process Control Valves (Q11–Q20)
Q11. What does the term “valve trim” refer to in process control valves?
a) External coating of the valve
b) Internal flow-controlling components
c) Actuator mounting structure
d) Valve body material
Correct Answer: b
Explanation: Valve trim includes internal parts such as the plug, seat, cage, and stem that control fluid flow in process control valves.
Q12. Which type of control valve is most suitable for throttling applications?
a) Gate valve
b) Globe valve
c) Check valve
d) Plug valve
Correct Answer: b
Explanation: Globe valves provide good throttling characteristics and precise control, making them common in process control valves applications.
Q13. What is the function of the valve bonnet in control valves?
a) Control flow rate
b) House the actuator
c) Seal the valve stem and connect body to actuator
d) Reduce pressure drop
Correct Answer: c
Explanation: The bonnet provides a pressure boundary and contains the stem sealing arrangement in process control valves.
Q14. Which valve characteristic provides a constant change in flow for a constant change in valve travel?
a) Equal percentage
b) Quick opening
c) Linear
d) Modified equal percentage
Correct Answer: c
Explanation: Linear characteristics provide a proportional relationship between valve travel and flow in process control valves.
Q15. Which valve characteristic is preferred for wide range flow control in control valves?
a) Linear
b) Quick opening
c) Equal percentage
d) On-off
Correct Answer: c
Explanation: Equal percentage characteristics are suitable for applications with large variations in flow demand.
Q16. What happens when control valves operate under cavitation conditions?
a) Valve flow increases
b) Vapor bubbles form and collapse
c) Valve closes automatically
d) Pressure remains constant
Correct Answer: b
Explanation: Cavitation occurs when vapor bubbles form and collapse, causing noise, vibration, and damage to process control valves.
Q17. Which factor has the greatest influence on sizing control valves?
a) Valve color
b) Actuator brand
c) Required flow rate and pressure drop
d) Pipe insulation
Correct Answer: c
Explanation: Proper sizing of process control valves depends mainly on flow rate, pressure drop, and fluid properties.
Q18. What does “fail-open” mean in control valves?
a) Valve opens when signal increases
b) Valve closes during normal operation
c) Valve opens when power or air fails
d) Valve remains fixed
Correct Answer: c
Explanation: In fail-open configuration, process control valves move to the open position during signal or air failure.
Q19. Which actuator type is used when very high force is required in control valves?
a) Pneumatic diaphragm
b) Electric actuator
c) Hydraulic actuator
d) Manual actuator
Correct Answer: c
Explanation: Hydraulic actuators provide high force output and are used in heavy-duty process control valves applications.
Q20. What is the purpose of a cage in cage-guided control valves?
a) Increase flow noise
b) Guide the valve plug
c) Seal the valve body
d) Mount the actuator
Correct Answer: b
Explanation: The cage guides the plug and helps stabilize flow in cage-guided process control valve
Objective Questions on Process Control Valves (Q21–Q30)
Q21. Which material is commonly used for valve seats in control valves handling high temperatures?
a) PTFE
b) Rubber
c) Metal
d) Elastomer
Correct Answer: c
Explanation: Metal seats are preferred in process control valves for high-temperature and severe service applications.
Q22. What does “installed valve characteristic” mean in control valves?
a) Valve behavior under laboratory conditions
b) Relationship between flow and valve travel in actual piping
c) Manufacturer’s rated Cv curve
d) Actuator force curve
Correct Answer: b
Explanation: Installed characteristics describe how process control valves behave in real systems where pressure drop varies with flow.
Q23. Which type of control valve is best suited for on-off service?
a) Linear characteristic valve
b) Equal percentage valve
c) Quick opening valve
d) Cage-guided valve
Correct Answer: c
Explanation: Quick opening valves allow rapid increase in flow and are suitable for on-off service in process control valves.
Q24. What is the function of a stem in control valves?
a) Control pressure rating
b) Transmit actuator motion to valve plug
c) Seal the process fluid
d) Reduce cavitation
Correct Answer: b
Explanation: The stem connects the actuator to the valve plug and transfers motion in process control valves.
Q25. Which condition causes flashing in control valves?
a) Pressure recovers above vapor pressure
b) Pressure drops below vapor pressure and does not recover
c) Valve fully closes
d) Flow becomes choked
Correct Answer: b
Explanation: Flashing occurs when pressure falls below vapor pressure and remains low downstream in process control valves.
Q26. What is the purpose of packing in control valves?
a) Increase flow capacity
b) Seal the stem to prevent leakage
c) Reduce valve weight
d) Improve flow characteristic
Correct Answer: b
Explanation: Packing prevents process fluid leakage along the valve stem in process control valves.
Q27. Which parameter is used to evaluate noise generation in control valves?
a) Cv
b) Reynolds number
c) Sound pressure level
d) Valve travel
Correct Answer: c
Explanation: Noise in process control valves is measured using sound pressure level, usually in decibels (dB).
Q28. Which type of body design provides the lowest pressure drop in control valves?
a) Globe valve body
b) Angle body
c) Straight-through body
d) Three-way body
Correct Answer: c
Explanation: Straight-through body designs offer smoother flow paths and lower pressure drop in process control valves.
Q29. What does “rangeability” refer to in control valves?
a) Maximum pressure rating
b) Ratio of maximum to minimum controllable flow
c) Valve size range
d) Actuator stroke length
Correct Answer: b
Explanation: Rangeability defines how effectively process control valves control flow over a wide operating range.
Q30. Which condition can cause erosion in control valves?
a) Low flow velocity
b) Clean fluid
c) High velocity with suspended particles
d) Stable pressure
Correct Answer: c
Explanation: High velocity flow with solid particles causes erosion and damage in process control valve
Objective Questions on Process Control Valves (Q31–Q40)
Q31. What is the main advantage of using a valve positioner in control valves?
a) Increase valve size
b) Improve valve accuracy and response
c) Reduce pressure rating
d) Eliminate actuator
Correct Answer: b
Explanation: A valve positioner improves positioning accuracy and response speed in process control valves.
Q32. Which fluid property has the most influence on control valves sizing?
a) Color
b) Density and viscosity
c) Electrical conductivity
d) Transparency
Correct Answer: b
Explanation: Density and viscosity significantly affect flow behavior and sizing of process control valves.
Q33. Which valve action opens the valve when the control signal increases?
a) Reverse acting
b) Fail-close
c) Direct acting
d) Fail-open
Correct Answer: c
Explanation: In direct-acting process control valves, an increase in control signal opens the valve.
Q34. Which type of trim is commonly used to reduce noise in control valves?
a) Standard trim
b) Soft seat trim
c) Multi-hole or cage trim
d) Rubber-lined trim
Correct Answer: c
Explanation: Multi-hole and cage trims help reduce turbulence and noise in process control valves.
Q35. Which problem occurs when control valves are oversized?
a) Improved accuracy
b) Increased rangeability
c) Poor control at low flow
d) Lower installation cost
Correct Answer: c
Explanation: Oversized process control valves operate near the closed position, leading to unstable control.
Q36. Which valve body style allows mixing or diverting service in control valves?
a) Two-way valve
b) Angle valve
c) Three-way valve
d) Butterfly valve
Correct Answer: c
Explanation: Three-way process control valves are used for mixing or diverting flow paths.
Q37. Which phenomenon causes vibration and noise due to vapor bubble collapse in control valves?
a) Flashing
b) Choked flow
c) Cavitation
d) Laminar flow
Correct Answer: c
Explanation: Cavitation causes vapor bubbles to collapse, leading to vibration and damage in process control valves.
Q38. What is the main function of a diaphragm actuator in control valves?
a) Measure pressure
b) Convert air pressure into linear motion
c) Control fluid temperature
d) Reduce noise
Correct Answer: b
Explanation: Diaphragm actuators convert pneumatic pressure into linear motion for process control valves.
Q39. Which type of control valve is commonly used for large diameter pipelines?
a) Globe valve
b) Needle valve
c) Butterfly valve
d) Plug valve
Correct Answer: c
Explanation: Butterfly valves are lightweight and economical for large pipe sizes in process control valves.
Q40. What does “seat leakage class” indicate in control valves?
a) Pressure rating
b) Flow coefficient
c) Allowable leakage rate
d) Valve size
Correct Answer: c
Explanation: Seat leakage class defines the maximum allowable leakage through closed process control valves.
Objective Questions on Process Control Valves (Q41–Q50)
Q41. Which standard defines seat leakage classes for control valves?
a) ASME B31.3
b) API 598
c) ANSI FCI 70-2
d) ISO 9001
Correct Answer: c
Explanation: ANSI FCI 70-2 specifies seat leakage classes for process control valves.
Q42. What is the primary purpose of a solenoid valve in control valves systems?
a) Throttle flow continuously
b) Convert electrical signal to mechanical motion
c) Act as an on-off pilot valve
d) Reduce line pressure
Correct Answer: c
Explanation: Solenoid valves are used as on-off pilot valves in process control valves systems.
Q43. Which failure can occur if packing is overtightened in control valves?
a) Increased leakage
b) Stem binding and poor response
c) Lower pressure drop
d) Higher Cv
Correct Answer: b
Explanation: Overtightened packing increases friction and affects the movement of process control valves.
Q44. Which type of actuator is preferred where fast response is required in control valves?
a) Manual actuator
b) Electric actuator
c) Pneumatic actuator
d) Hydraulic actuator
Correct Answer: c
Explanation: Pneumatic actuators provide fast response and are commonly used in process control valves.
Q45. What does “dead band” mean in control valves?
a) Maximum operating pressure
b) Range where valve does not respond to signal changes
c) Valve fully open position
d) Valve leakage rate
Correct Answer: b
Explanation: Dead band is the range of input signal where process control valves show no movement.
Q46. Which type of control valve is most suitable for slurry applications?
a) Globe valve
b) Ball valve
c) Knife gate valve
d) Needle valve
Correct Answer: c
Explanation: Knife gate valves handle slurries effectively due to their straight-through flow path.
Q47. What is the function of an air filter regulator in control valves systems?
a) Increase air pressure
b) Clean and regulate instrument air
c) Control valve position
d) Reduce flow noise
Correct Answer: b
Explanation: Air filter regulators supply clean and regulated air to process control valves actuators.
Q48. Which term describes the maximum allowable pressure drop across control valves without damage?
a) Working pressure
b) Choking pressure
c) Critical pressure drop
d) Operating pressure
Correct Answer: c
Explanation: Critical pressure drop defines the limit before choked flow or damage occurs in process control valves.
Q49. Which condition leads to hunting in control valves?
a) Proper sizing
b) Stable control loop
c) Oversized valve
d) Clean fluid
Correct Answer: c
Explanation: Oversized process control valves often cause oscillation or hunting due to poor controllability.
Q50. Which material is commonly used for soft seats in control valves?
a) Stainless steel
b) Carbon steel
c) PTFE
d) Cast iron
Correct Answer: c
Explanation: PTFE is widely used as a soft seat material in process control valves due to good sealing and chemical resistance.
Objective Questions on Process Control Valves (Q51–Q60)
Q51. What is the main purpose of a control valve body in control valves?
a) Convert signal to motion
b) Provide pressure containment and flow path
c) Seal the valve stem
d) Regulate air supply
Correct Answer: b
Explanation: The valve body forms the main pressure boundary and provides the flow passage in process control valves.
Q52. Which type of stem motion is used in globe-type control valves?
a) Rotary
b) Linear
c) Oscillatory
d) Sliding
Correct Answer: b
Explanation: Globe-type process control valves use linear stem motion to control flow.
Q53. Which phenomenon occurs when liquid pressure recovers above vapor pressure downstream of control valves?
a) Flashing
b) Cavitation
c) Choked flow
d) Laminar flow
Correct Answer: b
Explanation: Cavitation occurs when vapor bubbles collapse as pressure recovers downstream of process control valves.
Q54. What is the primary function of a feedback spring in control valves positioners?
a) Increase actuator force
b) Improve flow capacity
c) Balance input signal with valve position
d) Reduce air consumption
Correct Answer: c
Explanation: The feedback spring balances the input signal with actual valve position in process control valves.
Q55. Which parameter indicates how quickly control valves respond to a signal change?
a) Cv
b) Response time
c) Seat leakage class
d) Pressure rating
Correct Answer: b
Explanation: Response time defines how fast process control valves move to a new position after a signal change.
Q56. Which valve type provides tight shutoff in control valves applications?
a) Butterfly valve
b) Ball valve
c) Globe valve
d) Angle valve
Correct Answer: b
Explanation: Ball valves offer tight shutoff and are commonly used in process control valves for isolation duties.
Q57. What causes stiction in control valves?
a) Low friction
b) Excessive lubrication
c) High packing friction
d) Proper sizing
Correct Answer: c
Explanation: High packing friction causes stiction, leading to poor movement in process control valves.
Q58. Which standard is commonly used for sizing control valves?
a) ISA S75
b) IEC 60079
c) ISO 14001
d) API 650
Correct Answer: a
Explanation: ISA S75 provides guidelines and equations for sizing process control valves.
Q59. Which type of actuator uses compressed air on both sides of the piston in control valves?
a) Single-acting actuator
b) Spring-return actuator
c) Double-acting actuator
d) Manual actuator
Correct Answer: c
Explanation: Double-acting actuators use air on both sides of the piston in process control valves.
Q60. What is the main purpose of travel stops in control valves?
a) Increase Cv
b) Limit valve opening and closing
c) Improve sealing
d) Reduce noise
Correct Answer: b
Explanation: Travel stops limit the maximum and minimum valve movement in process control valves.
Objective Questions on Process Control Valves (Q61–Q70)
Q61. What is the main purpose of a yoke in control valves?
a) Control fluid flow
b) Support the actuator and connect it to the valve body
c) Seal the valve stem
d) Reduce pressure drop
Correct Answer: b
Explanation: The yoke provides structural support and connects the actuator to the valve body in process control valves.
Q62. Which condition causes choked flow in control valves handling gases?
a) Downstream pressure increases
b) Flow velocity becomes subsonic
c) Pressure drop reaches a critical value
d) Valve fully closes
Correct Answer: c
Explanation: Choked flow occurs when the pressure drop reaches a critical value and further reduction in downstream pressure does not increase flow in process control valves.
Q63. Which type of characteristic is commonly selected for pressure control using control valves?
a) Quick opening
b) Linear
c) Equal percentage
d) On-off
Correct Answer: c
Explanation: Equal percentage characteristics are preferred for pressure control applications using process control valves.
Q64. What is the primary function of a limit switch in control valves?
a) Control flow rate
b) Provide valve position indication
c) Regulate air pressure
d) Reduce leakage
Correct Answer: b
Explanation: Limit switches provide open or closed position feedback in process control valves.
Q65. Which valve body material is commonly used for corrosive service in control valves?
a) Cast iron
b) Carbon steel
c) Stainless steel
d) Brass
Correct Answer: c
Explanation: Stainless steel offers good corrosion resistance and is widely used in process control valves for corrosive applications.
Q66. What is the function of a handwheel in process control valves?
a) Automatic flow control
b) Emergency manual operation
c) Pressure regulation
d) Noise reduction
Correct Answer: b
Explanation: A handwheel allows manual operation of process control valves during maintenance or emergencies.
Q67. Which type of packing reduces friction in control valves?
a) Graphite packing
b) PTFE packing
c) Metal packing
d) Rubber packing
Correct Answer: b
Explanation: PTFE packing provides low friction and smooth stem movement in process control valves.
Q68. What is the effect of high supply air pressure on process control valves?
a) Reduced actuator force
b) Slower valve response
c) Increased actuator force
d) Lower Cv
Correct Answer: c
Explanation: Higher supply air pressure increases actuator force in process control valves.
Q69. Which valve type is commonly used for rotary motion in control valves?
a) Globe valve
b) Needle valve
c) Ball valve
d) Diaphragm valve
Correct Answer: c
Explanation: Ball valves operate using rotary motion and are widely used in process control valves applications.
Q70. What does “stroking” a valve mean in process control valves?
a) Replacing the actuator
b) Moving the valve through its full travel
c) Increasing valve size
d) Measuring pressure drop
Correct Answer: b
Explanation: Stroking involves moving process control valves from fully closed to fully open to verify operation.
Objective Questions on Process Control Valves (Q71–Q80)
Q71. Which factor mainly determines the actuator size for process control valves?
a) Valve color
b) Required thrust or torque
c) Pipe diameter
d) Ambient temperature
Correct Answer: b
Explanation: Actuator sizing for process control valves depends on the thrust or torque required to move the valve against process forces.
Q72. Which condition can cause seat wear in control valves?
a) Low flow velocity
b) Clean fluid
c) Frequent throttling near closed position
d) Stable pressure
Correct Answer: c
Explanation: Continuous throttling near the seat causes erosion and wear in process control valves.
Q73. Which accessory is used to lock process control valves in a fixed position?
a) Positioner
b) Limit switch
c) Lock-up valve
d) Air filter regulator
Correct Answer: c
Explanation: A lock-up valve holds the actuator pressure to keep process control valves in a fixed position during air failure.
Q74. What is the main purpose of a quick exhaust valve in control valves systems?
a) Increase flow capacity
b) Reduce actuator pressure slowly
c) Vent air quickly to speed up valve action
d) Filter instrument air
Correct Answer: c
Explanation: Quick exhaust valves vent air rapidly to improve response time of process control valves.
Q75. Which valve type provides good control for low flow rates in process control valves?
a) Butterfly valve
b) Globe valve
c) Needle valve
d) Ball valve
Correct Answer: c
Explanation: Needle valves allow fine control of low flow rates and are used in specific process control valves applications.
Q76. Which standard provides terminology and symbols for control valves?
a) ISA S5.1
b) API 6D
c) ISO 15649
d) IEC 60534
Correct Answer: a
Explanation: ISA S5.1 defines instrumentation symbols and terminology, including those for process control valves.
Q77. What happens if instrument air pressure drops below minimum in process control valves?
a) Valve opens fully
b) Valve closes fully
c) Valve moves to fail-safe position
d) Valve increases Cv
Correct Answer: c
Explanation: On low air pressure, process control valves move to their designed fail-safe position.
Q78. Which flow regime is desirable for stable operation of control valves?
a) Turbulent
b) Laminar
c) Transitional
d) Sonic
Correct Answer: a
Explanation: Turbulent flow provides stable and predictable control behavior in process control valves.
Q79. Which parameter is used to classify flow regime in process control valves?
a) Cv
b) Reynolds number
c) Pressure rating
d) Valve travel
Correct Answer: b
Explanation: Reynolds number is used to determine flow regime for sizing and performance of process control valves.
Q80. Which condition increases vibration in control valves?
a) Low pressure drop
b) Smooth flow path
c) High velocity and turbulence
d) Proper sizing
Correct Answer: c
Explanation: High velocity and turbulent flow increase vibration in process control valves.
Objective Questions on Process Control Valves (Q81–Q90)
Q81. What is the main purpose of a diaphragm in diaphragm-type control valves?
a) Increase flow capacity
b) Separate process fluid from actuator
c) Reduce noise
d) Improve Cv
Correct Answer: b
Explanation: The diaphragm isolates the process fluid from the actuator in diaphragm-type process control valves.
Q82. Which type of process control valve is commonly used in sanitary applications?
a) Gate valve
b) Butterfly valve
c) Diaphragm valve
d) Plug valve
Correct Answer: c
Explanation: Diaphragm valves are suitable for sanitary applications due to their smooth and cleanable design.
Q83. What is the function of a valve stem guide in control valves?
a) Increase flow
b) Reduce noise
c) Maintain alignment of stem and plug
d) Improve sealing
Correct Answer: c
Explanation: Stem guides maintain alignment and ensure smooth operation of process control valves.
Q84. Which actuator characteristic affects stability of process control valves most?
a) Actuator color
b) Actuator stiffness
c) Actuator size relative to valve
d) Actuator mounting
Correct Answer: c
Explanation: Correct actuator sizing ensures stable operation of process control valves.
Q85. Which valve is preferred for high-pressure drop liquid service in control valves?
a) Butterfly valve
b) Globe valve
c) Gate valve
d) Check valve
Correct Answer: b
Explanation: Globe valves handle high pressure drop liquid service effectively in process control valves.
Q86. What does “bench set” mean in spring-diaphragm control valves?
a) Valve operating pressure
b) Spring calibration range
c) Maximum supply pressure
d) Seat leakage class
Correct Answer: b
Explanation: Bench set refers to the spring pressure range required to move the valve in process control valves.
Q87. Which accessory provides continuous position feedback in control valves?
a) Limit switch
b) Pressure gauge
c) Position transmitter
d) Solenoid valve
Correct Answer: c
Explanation: Position transmitters provide continuous valve position feedback in process control valves.
Q88. What happens if control valves are undersized?
a) Poor control at low flow
b) Valve remains closed
c) Excessive pressure drop
d) Reduced noise
Correct Answer: c
Explanation: Undersized process control valves cause excessive pressure drop and limit flow capacity.
Q89. Which valve type uses a rotating disc in control valves?
a) Globe valve
b) Ball valve
c) Butterfly valve
d) Diaphragm valve
Correct Answer: c
Explanation: Butterfly valves use a rotating disc to control flow in process control valves.
Q90. What is the main purpose of calibration in control valves systems?
a) Increase valve size
b) Match valve movement with control signal
c) Reduce pressure rating
d) Change flow characteristic
Correct Answer: b
Explanation: Calibration ensures that process control valves respond accurately to control signals.
Objective Questions on Process Control Valves (Q91–Q100)
Q91. Which type of valve characteristic is best suited for level control using process control valves?
a) Quick opening
b) Linear
c) Equal percentage
d) On-off
Correct Answer: c
Explanation: Equal percentage characteristics are commonly used for level control with process control valves due to varying process gains.
Q92. What is the purpose of a booster relay in control valves systems?
a) Reduce signal pressure
b) Increase air volume to actuator
c) Filter instrument air
d) Indicate valve position
Correct Answer: b
Explanation: Booster relays supply higher air volume to improve the response speed of process control valves.
Q93. Which type of process control valve is commonly used for corrosive slurry service?
a) Globe valve
b) Ball valve
c) Diaphragm valve
d) Butterfly valve
Correct Answer: c
Explanation: Diaphragm valves isolate the actuator from the process fluid and handle corrosive slurry service in process control valves.
Q94. What does “actuator spring range” indicate in control valves?
a) Maximum valve pressure
b) Input signal range for full stroke
c) Valve size
d) Seat leakage rate
Correct Answer: b
Explanation: Spring range defines the signal pressure required to move process control valves from closed to open.
Q95. Which phenomenon is more common in gas service process control valves at high pressure drop?
a) Cavitation
b) Flashing
c) Choked flow
d) Laminar flow
Correct Answer: c
Explanation: Choked flow occurs in gas service process control valves when pressure drop reaches a critical level.
Q96. What is the main purpose of a valve nameplate in control valves?
a) Decorative identification
b) Provide operating and sizing information
c) Indicate actuator color
d) Reduce installation errors
Correct Answer: b
Explanation: Nameplates provide essential data such as size, Cv, pressure rating, and materials for process control valves.
Q97. Which maintenance activity helps extend the life of control valves?
a) Oversizing the valve
b) Ignoring leakage
c) Regular inspection and lubrication
d) Increasing pressure drop
Correct Answer: c
Explanation: Routine inspection and proper lubrication reduce wear and improve reliability of process control valves.
Q98. Which valve type is commonly used for mixing applications in process control valves systems?
a) Two-way valve
b) Angle valve
c) Three-way valve
d) Butterfly valve
Correct Answer: c
Explanation: Three-way valves are used for mixing or diverting flow in process control valves systems.
Q99. What is the function of a fail-safe action in control valves?
a) Improve flow capacity
b) Maintain safety during failure conditions
c) Increase response speed
d) Reduce operating cost
Correct Answer: b
Explanation: Fail-safe action ensures process safety by moving process control valves to a predefined position during failures.
Q100. Why are control valves essential in closed-loop control systems?
a) They measure process variables
b) They generate control signals
c) They act as final control elements
d) They store process data
Correct Answer: c
Explanation: Process control valves act as final control elements, executing the control action based on controller output.
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