Explain the working of valve actuators used in control valve.
Working of spring diaphragm actuator: Actuator is the portion of the valve that responds to the applied signal and results in the movement of the stem due to which the flow rate of fluid changes. It consists of a pressure tight housing sealed by a flexible diaphragm, stem and diaphragm returning spring. Signal air pressure from the controller is applied to upper diaphragm case, that exerts force on the diaphragm and the actuator assrmbly.by selecting proper spring rate or stiffness, desired stem displacement can be obtained for any given input signal. The diaphragm is made of neoprene or any other synthetic elastic element.