This article describes the Top 10 Control Valve Questions and Answers. The control valve is a vital device for process control and is widely used in all types of industries.
We will discuss the following Top 10 Control Valve Questions and Answers
Q.1 What is a control valve and where is it used?
A control valve is a type of instrument used to control the flow of any liquid, gas, or even slurries flowing through a line. The control valve is mainly used as a controlling device in lines to maintain flow, pressure, temperature, or even level by controlling the flow of the fluid flowing through it.
Q.2 What are the main components of a control valve?
A control valve has 3 main components. One is the actuator of the control valve, the second one is the body of the control valve and the third one is the brain of the control valve, i.e. positioner of the control valve. The actuator operates the body of the control valve through the air supply/signal given to it. Actuator receives the air signal from the positioner. Hence, these 3 (actuator, body, and positioner) together form a complete control valve that maintains our desired parameter.
Q.3 What are the types of actuators used in a control valve?
There are 4 main types of control valve actuators. They are pneumatic actuators, hydraulic actuators, electric actuators, and electro-hydraulic actuators.
Q.4 What are the types of bodies used in a control valve?
The main types of control valve bodies are globe valves, butterfly valves, ball valves, diaphragm valves, and pinch valves.
Q.5 What are the main types of actuators based on their operation?
Totally there are 3 main types of actuators based on their operation.
- Air Fail Open Actuator (also called Air to Close Actuator)
- Air Fail Close Actuator (also called Air to Open Actuator)
- Air Fail Lock Actuator
Q.6 What is the difference between a fail open valve, fail close valve, and a fail lock valve?
- Fail open valve means that whenever the air to the valve or the electric supply to the solenoid valve is lost, the valve will open.
- Fail close valve means that whenever the air to the valve or the electric supply to the solenoid valve is lost, the valve will close.
- A fail lock valve means that whenever the air to the valve or the electric supply to the solenoid valve is lost, the valve will stay in that condition only.
Q.7 What is the control valve leakage class? What are the types of control valve leakage classes with specifications?
Control valve leakage class tells about the amount of leakage which is permissible in that particular leakage class. Totally 6 leakage classes for a control valve are present. All of them are mentioned below with their specifications.
- Class I: No leakage test required
- Class II: 0.5% leakage permissible of full open valve capacity with service DP or 50 psid pressure (whichever is lower at 50 deg F to 125 deg F). Also, the test medium is air or water at 45 psig to 60 psig is the test fluid
- Class III: 0.1% leakage permissible of full open valve capacity with service DP or 50 psid pressure (whichever is lower at 50 deg F to 125 deg F). Also, the test medium is air or water at 45 psig to 60 psig is the test fluid
- Class IV: 0.01% leakage permissible of full open valve capacity with service DP or 50 psid pressure (whichever is lower at 50 deg F to 125 deg F). Also, the test medium is air or water at 45 psig to 60 psig is the test fluid
- Class V: Maximum leakage allowed is limited to only 5 x 10-4 ml per minute per inch of orifice diameter per psi differential with test fluid as water at 100 psig or operating pressure.
- Class VI: The leakage should not exceed the amounts mentioned above. Here the test medium is air or nitrogen at 50 deg F to 125 deg F.
Q,8 Which is the most common type of leakage class of control valve used in the field?
Class I, class IV, and class VI leakage-type control valve are most commonly used in the field.
Q.9 What are the types of control valve flow characteristics?
There are three main flow characteristics of a control valve.
- Linear
- Quick Opening
- Equal Percentage
Q.10 What are the accessories of a control valve?
Accessories of a control valve are
- Solenoid valve
- Positioner
- Air volume booster
- Trip valve
- Limit switches
- Position transmitter
- Handwheel
