Expert’s answer : Types of control valve actuators
When you’re scaling out a new control valve, vendors should support you with all the specifications and recommend the right type for your application. If your vendor doesn’t do that, then you should find another vendor.
Now that you know that, let’s talk about how an actuator works. It receives commands from the control system to create a force that moves a control valve. And it does this either directly or through the valve positioner, which converts your digital or analog signal to pneumatic output.
Here we have five types of control valve actuators commonly used. So let’s take a quick look at each.
This type has a flexible diaphragm with pressure applied against the force of the actuator spring. When the control system sends its signal, the actuator creates a force that overcomes the force of the spring, moving the actuator stem.
You have two types of action in a pneumatic actuator, direct and reverse. Direct action means the actuator pushes the stem down and the spring pushes it up. Reverse action will move the stem up, and the spring moves it down.
This one works much like an actuator with a diaphragm and spring. However, this actuator replaces the diaphragm with a piston. We have two types of action here too, linear and rotating. As you may have guessed, linear moves the actuator component in a straight line and rotating turns it. We have another post that explains that a little more here.
This actuator has a motor and gearbox to create torque that moves the valve up and down. You can find this type in linear and rotating control valves.
This type mixes electric signals and hydraulic units to act on the valve. The signal will control the flow of oil to open and close the valve, using a flapper-nozzle system similar to a pneumatic system.
This one works much like a pneumatic actuator, and you can use it in linear and rotating control valves. However, it uses fluid rather than air to create force in its system.
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