Control Valves and Actuators — MCQs – EE

1. The control valve in a process control system functions as:
(A) Measuring device
(B) Final control element
(C) Controller
(D) Transmitter

2. The primary function of a control valve is to:
(A) Measure process variables
(B) Regulate the flow of fluid
(C) Generate electrical signals
(D) Indicate temperature

3. The actuator in a control valve assembly provides:
(A) The mechanical motion to operate the valve
(B) Signal transmission
(C) Temperature measurement
(D) Pressure indication

4. The signal input to a pneumatic actuator is typically:
(A) 4–20 mA
(B) 3–15 psi
(C) 0–5 V
(D) 0–10 V

5. The signal input to an electric actuator is generally:
(A) 4–20 mA or 0–10 V
(B) 3–15 psi
(C) Mechanical linkage
(D) Hydraulic pressure

6. A pneumatic actuator converts:
(A) Electrical energy into motion
(B) Air pressure into mechanical motion
(C) Hydraulic pressure into voltage
(D) Current into torque

7. A hydraulic actuator converts:
(A) Fluid pressure into mechanical force
(B) Voltage into pressure
(C) Torque into flow
(D) Flow into electrical energy

8. A control valve positioner is used to:
(A) Ensure valve reaches desired position accurately
(B) Measure process flow
(C) Act as a sensor
(D) Replace the controller

9. The linear motion valve includes:
(A) Globe and gate valves
(B) Butterfly and ball valves
(C) Plug and rotary valves
(D) Piston and poppet valves

10. The rotary motion valve includes:
(A) Globe valve
(B) Butterfly and ball valves
(C) Diaphragm valve
(D) Gate valve

11. A globe valve is preferred for:
(A) On–off service
(B) Precise flow control applications
(C) Isolation only
(D) Non-regulating service

12. A ball valve is mainly used for:
(A) Throttling service
(B) Quick on–off operation
(C) Precise flow regulation
(D) High viscosity control

13. A butterfly valve is best suited for:
(A) Large-diameter, low-pressure flow control
(B) High-pressure, low-flow systems
(C) Thermal measurement
(D) Small bore pipes only

14. A diaphragm actuator converts:
(A) Air pressure to valve stem motion
(B) Electrical signal to temperature
(C) Fluid flow to torque
(D) Mechanical vibration to displacement

15. The valve body determines:
(A) Flow characteristics and pressure handling capacity
(B) Electrical control logic
(C) Signal transmission
(D) Temperature range only

16. The plug and seat in a control valve form the:
(A) Measuring element
(B) Flow control orifice
(C) Actuator mechanism
(D) Electrical connector

17. The valve trim includes:
(A) Plug, seat, and stem
(B) Actuator and positioner
(C) Controller and transmitter
(D) Bonnet and gasket

18. The valve bonnet serves as:
(A) A cover for the valve body and support for stem
(B) A measuring element
(C) An actuator
(D) A positioner

19. The flow characteristic of a valve defines:
(A) The relationship between valve opening and flow rate
(B) The material of construction
(C) Pressure rating only
(D) The temperature coefficient

20. The equal percentage valve characteristic provides:
(A) Small changes in flow at small openings and large changes at large openings
(B) Linear flow relation
(C) Constant flow regardless of opening
(D) On–off behavior

21. The linear valve characteristic means:
(A) Flow rate changes linearly with valve opening
(B) Flow increases exponentially
(C) Flow decreases with opening
(D) Flow is independent of position

22. A quick-opening valve characteristic is ideal for:
(A) On–off control
(B) Proportional control
(C) Flow measurement
(D) Temperature sensing

23. Cavitation in control valves occurs when:
(A) Liquid vaporizes and collapses due to pressure changes
(B) Gas expands inside the valve
(C) Flow becomes laminar
(D) Temperature remains constant

24. Flashing in a control valve occurs when:
(A) Vapor bubbles form and remain in the liquid stream
(B) Pressure increases sharply
(C) Valve stem sticks
(D) Fluid temperature drops

25. A fail-safe actuator is designed to:
(A) Move valve to a safe position upon power failure
(B) Keep valve fully open at all times
(C) Shut down the system completely
(D) Bypass the controller

26. A spring-return actuator ensures:
(A) The valve moves to a safe position on loss of air pressure
(B) The valve remains open on power failure
(C) The actuator operates continuously
(D) The positioner resets manually

27. A double-acting pneumatic actuator requires:
(A) Air pressure for both opening and closing actions
(B) Air only for opening
(C) Air only for closing
(D) No air supply

28. Valve hysteresis is:
(A) Difference in valve position for the same signal during increasing and decreasing strokes
(B) Signal amplification error
(C) Mechanical backlash in actuator
(D) Electrical delay in transmitter

29. Air-to-open control valve action means:
(A) Valve opens as air pressure increases
(B) Valve closes as air pressure increases
(C) Valve remains closed
(D) Valve position is unaffected by air pressure

30. Air-to-close control valve action means:
(A) Valve closes as air pressure increases
(B) Valve opens as air pressure increases
(C) Valve remains open
(D) Valve is unaffected

31. A smart valve positioner can:
(A) Receive and transmit digital communication signals
(B) Only convert pneumatic signals
(C) Eliminate actuator motion
(D) Control power supply

32. The valve coefficient (Cv) indicates:
(A) The flow capacity of a valve
(B) The power requirement
(C) The pressure drop
(D) The temperature limit

33. A solenoid valve operates using:
(A) Electromagnetic force
(B) Hydraulic pressure
(C) Pneumatic pressure
(D) Manual control

34. The control valve gain affects:
(A) System stability and response
(B) Pressure measurement only
(C) Temperature indication
(D) Sensor calibration

35. A position feedback sensor in an actuator ensures:
(A) Accurate valve positioning
(B) Manual override
(C) Temperature control
(D) Pressure reduction

36. The valve rangeability is the:
(A) Ratio of maximum controllable flow to minimum controllable flow
(B) Pressure range of the valve
(C) Mechanical size
(D) Power consumption

37. A digital valve controller (DVC) allows:
(A) Remote calibration and monitoring
(B) Manual operation only
(C) Air signal transmission only
(D) Mechanical feedback only

38. The actuator torque must be sufficient to:
(A) Overcome valve friction and process pressure
(B) Reduce valve noise
(C) Control signal amplitude
(D) Regulate current flow

39. A handwheel on a valve actuator is used for:
(A) Manual override operation
(B) Speed control
(C) Power adjustment
(D) Air regulation

40. Valve cavitation and flashing can be reduced by:
(A) Pressure staging or multi-trim design
(B) Increasing flow velocity
(C) Using smaller actuators
(D) Removing positioners