The purpose of the control valve actuator is to provide force to operate a valve mechanism.
Both rotary and sliding stem valve have the same type of actuator. There are four types of actuator you can find in the plant.
4. Hand operated
Let's learn about the pneumatic type of actuator in this article.
PNEUMATIC ACTUATOR :
A pneumatic actuator requires compressed air supply to operate a valve. The air supply is fed to piston type or diaphragm type assembly to move a valve.
Following image is shown cut view of the diaphragm type pneumatic valve actuator.
Here, you can see the valve actuator, when applying pressure from the top it will push down valve plug such operation know as air to close (ATC), large spring provides positioning of the valve.
The pressure applying from the downside will lift the valve plug such operation is known as air to open (ATO).
Spring is used with diaphragm assembly to allow relief of the pressure. This type of valve is known as single-acting as air pressure acts only in one direction.
In Double acting, air pressure acts from both sides as you can see in the below photograph.
In piston type of pneumatic actuator, to lift piston it comes with two arrangement, one if there is a piston with spring it only requires single tubing as shown ith below figure known as single-acting.
Double-acting it requires two tubings to lift and push piston as it doesn't have spring. Have a look into the below figure,