Control Valve Actuators: Basic Types and Designs
An actuator is an assembly fitted to the control valve to provide power for moving the move-able parts – plug, ball or vane. The operation of the control valve essentially involves positioning these move-able parts(plug, ball or vane) relative to the stationary seat of the valve. In view of this, the valve actuator performs two basic functions:
(1) Drive the move-able parts to a position required by the control signal
(2) Provide default positioning when there is no drive power available i.e close or open the valve or hold it steady in the present position.
In the valve control loop, the actuator accepts a signal from the control system and in response, moves the valve to either a fully open or fully close position or an intermediate position depending on whether ON/OFF or continuous control is used.
Types of Actuators for Control Valves
The actuator provides the drive power for the operation of the valve parts under all flow conditions of the control valve as well as hold it firmly shut when needed. Three principal types of actuator drive powers are in use today:
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