ABSTRACT
Operation of the closed-loop control system depends on the performance of each loop component, including the final control element, whether it be damper, variable speed pump, motor relay, saturable reactor, or valve. Each of these elements requires an actuator that will make the necessary conversion from controller output signal to element input. This controller output may be pneumatic or electric and in some cases hydraulic or mechanical. The pneumatic signal is applied to a large flexible diaphragm backed by a rigid diaphragm plate. Thus, the stem position is an equilibrium of forces that depends on diaphragm area, pneumatic pressure, and spring characteristic. Pneumatic spring-diaphragm actuators have many applications, the most common of which is the operation of a control valve. Spring-diaphragm actuators convert air signal pressure to force and motion and can be adapted to a large number of industrial requirements when precise loading or positioning is required.
