Fisher 657 Actuator Diaphragm pneumatic

Fisher 657 and 667 spring-opposed diaphragm actuators position the valve plug in the valve in response to varying controller or valve positioner pneumatic output signals applied to the actuator diaphragm. Zero setting of the actuator is determined by the compression of the actuator spring. Span is set by both the actuator spring rate and the number of springs available. The 657 actuator is direct-acting; the 667 is reverse-acting. These actuators are designed to provide dependable on-off or throttling operation of automatic control valves