Control valve is a Final control element .Final control elements are necessary to control the Process variable.
Valves are used to control the flow of fluid in process system.
Main parts of Control valve are Valve Body and Actuator
Actuators are used to position the valves.
Actuator is a mechanism which moves or control a device such as a valve.
3 Basic types of Actuators are there
Pneumatic actuators use air pressure to produce motion to position a valve.
Actuator that are powered by a pressurized liquids such as hydraulic fluid are called
Hydraulic actuators .Hydraulic actuators are more powerful.
Electric Actuators use electricity to produce motion
Electric actuator can be classified as two types - Solenoid actuators and Motor driven actuators
One of the most common example for Pneumatic actuators are Diaphragm Actuators
Basic parts of a control Valve Body
Valve position indicators
single acting - air pressure acts only one side of the diaphragm to position a valve
Double acting actuators -Air pressure acts on both sided of the diaphragm to position a valve