Fisher Pneumatic Actuators Fisher 657 and 667 spring-opposed diaphragm actuators
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.
- Application Versatility—Five actuator types in eleven sizes are available for an extensive variety of applications. Spring rates, travel stops, and manual operators are available for nearly any control valve application.
- Excellent Linearity Between Loading Pressure and Travel—A molded diaphragm travels in a deep diaphragm casing, minimizing area change throughout the travel.
- High Degree of Dynamic Stability and Frequency Response—A shallow casing on the pressure side means reduced volume on that side, thereby minimizing response time.
- High Thrust Capability—The molded diaphragm allows maximum thrust for given diaphragm size.
- Long Service Life—Rugged thick-walled cast iron and steel construction provides increased stability, corrosion protection, and protection from deformation should over-pressurization occur.
- Cold Service Applications—Enhanced product specifications for all sizes of 657 and 667 diaphragm actuators allow performance to -50°C (-58°F). Use of a positioner is recommended to ensure responsiveness in applications operating below -40°C (-40°F).
- Positive Connections—A split block stem connection provides a solid transfer of motion while allowing easy mounting. The absence of linkages helps to avoid lost motion and inaccurate valve positioning.
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