Actuation & Instrumentation
Actuator
The actuator is the muscle of a control valve: the device that converts a control signal — usually an air pressure or an electric command — into the mechanical motion (stroke or rotation) that repositions the throttling element inside the valve body.
Pneumatic actuators dominate process control. Diaphragm actuators are simple and reliable for globe valves; piston actuators offer higher thrust for larger valves or higher pressure drops. Electric actuators suit locations without instrument air and duties needing precise positioning with high stiffness.
Actuator sizing is as important as body sizing: the actuator must overcome process unbalance forces plus packing friction in both directions, with margin, at the worst-case differential pressure — otherwise the valve will not seat, will not stroke, or will hunt.