Control valves and their opening for fluid to pass through, is operated via actuators. This post is a detailed description of different parts of a control actuator and how it works.
Following are critical parts of actuator of control valve and their information
A. Loading Pressure Connection
Loading Pressure Connection is the location where pneumatic (Air or gas) medium enters the actuator body. Location of this depends on valve shall be resting position i.e. position in case of failure in pneumatic medium. For fail open valves the loading pressure connection is from the top side and for fail close valve the loading pressure connection is from the bottom side.
Diaphragm is the moving part of actuator and based on the pressure supplied from loading pressure connection it moves up and down to give guiding action control the valve opening.
C. Actuator spring
Actuator spring guides the valve position in case of the failure of the pneumatic supply. Spring plays the role of failsafe conditions and is very critical from safety point go view. The location of spring is different for different failsafe conditions. The actuator spring is housed below loading pressure connection in case of fail open valve and it is housed above loading pressure connection in case of fail close.
D. Actuator stem
Actuator stem is the potion of actuator which connects the actuator to the valve stem. The guiding action from diaphragm is translated to valve plug via valve stem.
Yoke is the part of actuator which connects the actuator to the bonnet of the valve body. Yoke is surrounding the actuator stem with clearance.
Following figures given details of actuator parts -
To learn about different parts of a control valve and how they work, check out this detailed post.