Valve positioner and its working

Valve Positioner is a unit used on a control valve to keep the valve in position. It works as a booster relay with a valve stroke feed back. A controller output is fed to the valve positioner and the valve position provides an output to the control valve actuator to achieve the pre-calibrated stroke length. In case the require stroke length isnt achieved, then the positioner either increases or decreases its output until the valve achieves the desired stroke length. This situation may occur when there is a great change in the process pressure, gland is too tight…etc.