pneumatic,electric,hydraulic actuators and their working principle;applications and differences of all three types;The purpose of a control valve actuator is to provide the motive force to operate a valve mechanism.

Both sliding-stem and rotary control valves enjoy the same selection of actuators: pneumatic,

hydraulic, electric motor, and hand (manual).Pneumatic actuators use air pressure pushing against either a flexible diaphragm or a piston to move

a valve mechanism.