CONTROL VALVE ACTUATOR: TYPES AND DESIGN

CONTROL VALVE :

• It is a mechanical instrument which is used to control process variables (i.e. pressure, level, flow, temperature, etc.)  Within the required operating range and ensure quality of end product

• In automatic control terminology, A control valve is a termed  a “final control element”

• The valve controlling the process parameter by electrical, hydraulic or pneumatic actuators.

CONTROL VALVE ACTUATOR 

• An actuator is an assembly part of control valve which provides power to moving parts of the control valve like-plug ball or vane.

• The operation of the control valve essentially involves positioning these moveable parts relative to the stationary seat of the valve.

The actuator performs two basic function

1.  According to control signal drive moveable parts
2.  Provide default positioning when there is no drive power available. (i.e. Close or open the valve or hold it at the position)

• The actuator collects the signal from the control system according to that valve moves to either fully open or fully close or an intermediate position depending on whether ON/OFF or continuous control.

Mainly three types of actuators used in control valve

1.          Pneumatic
2.          Hydraulic
3.          Electrical

Pneumatic actuator:

• A pneumatic actuator covert energy ( compress air ) into mechanical energy.

• They are the most widely used method of actuation

• They are inherently safe against explosion hazards

• The motion can be rotary or linear depends on which type of pneumatic actuator is used in pneumatic actuator two types:

1. ·         Piston actuator
2. ·         Diaphragm actuator

Hydraulic actuator:

• Pneumatic actuator that used hydraulic fluid to move the valve

• Almost all hydraulic actuator design uses a piston rather than a diaphragm to convert fluid pressure into mechanical force

• They generate a huge amount of mechanical force hence they are used in large isolating valve in gas industries.

Electric actuator:

• The electrical actuator uses an electrical motor and a gear reduction drive to move the valve in a linear or rotary direction 

• They can be used for ON-OFF application for large isolation valve 

• It is widely used for continuous positioning control as feedback control sends to the controller. 

• They widely used in power generation plants, water supply, and pharmaceutical industries.