What is a control valve and what is its primary function?

A control valve is a final control element that regulates fluid flow by varying the opening of the flow passage in response to a control signal. It consists of a valve body (contains flow passage and trim), actuator (provides force to move the plug), and positioner (ensures accurate positioning). Control valves are the interface between the control system and the process, converting controller output (4-20 mA or digital signal) into physical action that affects process variables like flow, pressure, level, and temperature.