#WishIknew – How do control valves work?

Valves

When you have a question about process automation that needs a short answer, let us know with #WishIknew and @Visaya! We’ll reply with a #WishIknew post. It’ll give a quick explanation, then some related articles, videos, or reviews if you want to know more.

I wish I knew how control valves work!

A control valve is an essential part of a control system. In a controlled application, you have a product you must maintain at a certain point. The controller acts directly on the valve to change or sustain the quantity of product in a pipe or tank or whatever.

So the control valve has three main parts – actuator, valve body, and positioner. And each part has smaller pieces. The actuator has a spring, spring seat, diaphragm, and so on. You can have hydraulic, pneumatic or electric actuators. Valve bodies also come in different styles, such as globe, ball, or gate.

Courtesy of GlobalSpec

Let’s zoom back out to the control valve. You can operate it with electrical, pneumatic, or mechanical signals. To explain how it works, I’ve chosen a standard control valve that uses a pneumatic actuator and globe valve body. The air in the actuator will close or open the valve.

Now, the valve positioner receives a signal from the control system. Based on the signal, the positioner will send enough air to position the valve body in the right range. Then it measures feedback through the movement of the actuator stem.

In the valve body, the valve plug allows more or less product to pass through the body. The spring in the actuator will keep the valve in a natural position, closed or open depending on the valve’s action.

And that’s it, a control valve! Make sense? If not, drop me a comment!

This video should help too:

 

Related tags: #WishIknew Basic Control valves devices English Final Element Measurements Principle valves
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