hvac controls

What You Need to Know About Control Valves

What is a Control Valve?

To be able to control fluid, a control valves is used for varying the size of the passage’s flow which is directed by a signal controller.

It is also called the “final control element”.

What Does It Do?

As mentioned, the control valve regulates the flow of liquid or gas, by closing or opening the internal passages. The valve stem shifts allowing the passage’s size to increase, decrease, or stay put as it flows. When the process parameter does not match the set point, there is a resulting alteration when the control valve opens. Electrical, hydraulic, or pneumatic actuators are those that allow the opening or closing of the valves.

How Does It Work?

The valve, the actuator, and the controller are the three components of the control valve.

There are two basic types of valves. One is the plug design wherein the plug is closed and is opposed to a seat. The other is the seat design wherein a valve is quarter-turned and a disc, ball, or cone and is opposed to a seat.

An actuator moves the valve stem.

The controller calculates the change in the internal passages’ size and brings the desired flow rate. Usually, air and electricity drive them.

The flow’s rate through the valve lies in the difference of pressure between the outlet and inlet. When the flow needs to slow down, the valve closes. It allows for more back-pressure and a bigger difference in the pressures of the inlet and outlet. If the flow needs to increase, the valve opens. It reduces back-pressure, as well as the difference in the inlet and outlet.

Known as the valve trim, it is what regulates the flow in the control valve. It comprises of movable cone, ball, disc or plug. This trim can create different passage shapes that can deliberately control the flow.

The controller is the component that commands the valve’s response. The control valve’s tuning defines the intensity and speed of the response of the valve.

The process wherein the controller produces an output for the actuator involves:

  • the discrepancy in the size between the current value and the set point of the controlled parameter
  • the discrepancy in the length of time
  • the discrepancy in speed

It then determines the speed and distance of the stem

Note, however, that it is integral to buy the control valve that is meant for the pipeline you have. Also, make sure that the packaging of the valve is in perfect condition. If wrapped too tight, it will cause some damage.