Valve Types and Functions Quiz
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Questions and Answers

What is a disadvantage of using a gate valve for control applications?

  • More complex construction
  • Limited throttling capability (correct)
  • Requires high actuator force
  • Prone to cavitation

    • What is the primary function of an angle valve?

  • Regulates high-pressure applications
  • Offers a wider rangeability
  • Provides superior shutoff compared to globe valves
  • Changes flow direction (similar to an elbow with control capability) (correct)

    • A butterfly valve features a disc that rotates on a shaft to control flow. What is an advantage of this design?

  • Excellent throttling characteristics
  • High pressure rating
  • Compact and lightweight (correct)
  • Ideal for viscous fluids

    • Why is a positioner used with a control valve?

    <p>To improve the accuracy and stability of the valve position</p> Signup and view all the answers

    How does a positioner improve the performance of a control valve?

    <p>By compensating for pressure drops and friction in the actuator</p> Signup and view all the answers

    What is cavitation in a control valve, and what effect does it have?

    <p>Rapid formation and collapse of vapor bubbles due to pressure drop, causing vibration and erosion</p> Signup and view all the answers

    How can cavitation and flashing be prevented in control valves?

    <p>Reducing the pressure drop across the valve</p> Signup and view all the answers

    Which of the following is NOT a component of a basic process control loop?

    <p>Final product</p> Signup and view all the answers

    A temperature control system in a chemical reaction vessel is an example of a process loop for controlling which variable?

    <p>Temperature</p> Signup and view all the answers

    The current flowing through a transmitter in a process loop can be considered a:

    <p>Process variable</p> Signup and view all the answers

    In P&ID diagrams, a square box with a diagonal line represents:

    <p>Sensor</p> Signup and view all the answers

    Instruments located in the physical process area (near the equipment) are represented by symbols in the:

    <p>Top half of the P&amp;ID</p> Signup and view all the answers

    The standard 4-20mA current loop is used in process control because it is:

    <p>Both a) and b)</p> Signup and view all the answers

    In a pressure transmitter, a “live zero” calibration refers to adjusting the output signal when the:

    <p>Transmitter is powered on but no pressure applied</p> Signup and view all the answers

    Which of the following statements about dead zero is INCORRECT?

    <p>It should be done frequently during operation</p> Signup and view all the answers

    Why are transmitters used in process control systems?

    <p>To convert sensor signals into a standard format for easy transmission</p> Signup and view all the answers

    Which of the following terms indicates the main difference between a two-wire and a four-wire transmitter?

    <p>Power supply</p> Signup and view all the answers

    Which of the following is NOT a typical feature of a transmitter?

    <p>Flow control valve</p> Signup and view all the answers

    An electronic capacitive differential pressure transmitter (DPT) can be used for level measurement. How does this work?

    <p>By measuring the pressure difference between the top and bottom of a tank</p> Signup and view all the answers

    What is the drawback of using only proportional control?

    <p>Steady-state error (the process variable may not reach the setpoint)</p> Signup and view all the answers

    Integral control (I) eliminates the steady-state error of a proportional controller by considering:

    <p>The accumulation of past errors</p> Signup and view all the answers

    What is the potential issue with using only integral control?

    <p>Increase offset</p> Signup and view all the answers

    Derivative control (D) anticipates future changes in the error by considering the:

    <p>Rate of change of the error</p> Signup and view all the answers

    Which type of valve uses a disc that moves vertically to regulate flow?

    <p>Globe valve</p> Signup and view all the answers

    Study Notes

    • Process Control Loops*

    • A process control loop typically consists of a sensor, controller, actuator, and final control element

    • The sensor measures the process variable (PV) and sends the signal to the controller

    • The controller compares the PV to the setpoint (SP) and calculates the error

    • The actuator receives the controller's output signal and adjusts the final control element to manipulate the process variable

    • Components of a Process Loop*

    • Sensor: measures the process variable (PV) and sends a signal to the controller

    • Controller: compares the PV to the setpoint (SP) and calculates the error

    • Actuator: receives the controller's output signal and adjusts the final control element

    • Final Control Element: manipulates the process variable (e.g., valve, pump, heater)

    • P&ID Diagrams*

    • Symbols in the top half of the P&ID represent instruments located in the physical process area (near the equipment)

    • Symbols in the bottom half of the P&ID represent instruments located in the control room or remote locations

    • Transmitters*

    • Used to convert sensor signals into a standard format for easy transmission

    • Can be two-wire or four-wire transmitters

    • Two-wire transmitters receive power from the signal loop, while four-wire transmitters have a separate power connection

    • Can have features like internal diagnostics, remote calibration capability, and linear output signals

    • Differential Pressure Transmitters (DPTs)*

    • Can be used for level measurement by measuring the pressure difference between the top and bottom of a tank

    • Can have features like zero elevation and suppression to adjust the span of the transmitter and compensate for static pressure

    • Smart Transmitters*

    • Offer digital communication capabilities

    • Can perform internal diagnostics and have remote calibration capability

    • Can be configured and calibrated using a handheld device or computer

    • Control Systems*

    • Error: the difference between the desired output (setpoint) and the actual output

    • Cycling: rapid on-off switching of the final control element

    • Direct Acting: the controller output increases with an increase in the controlled variable

    • Reverse Acting: the controller output decreases with an increase in the controlled variable

    • PID Controllers*

    • Proportional (P) control: adjusts the control signal based on the magnitude of the error

    • Integral (I) control: eliminates steady-state error by considering the accumulation of past errors

    • Derivative (D) control: anticipates future changes in the error by considering the rate of change of the error

    • PI controllers use a combination of P and I control, while PID controllers use a combination of P, I, and D control

    • PID Controller Tuning*

    • Ziegler-Nichols method: a common method for tuning PID controllers

    • Relay tuning method: another method for tuning PID controllers

    • Genetic algorithm method: a method for tuning PID controllers using optimization techniques

    • Final Control Elements*

    • Control valves: manipulate the process variable (e.g., flow rate, pressure, temperature)

    • Actuators: power the movement of the control valve (e.g., pneumatic, electric)

    • Valve trim: the internal parts of the control valve that come into contact with the process fluid

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    Test your knowledge of different types of valves, their functions and applications. Learn about gate valves, angle valves, and more.

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