Fisher 657 and 667 Diaphragm Actuators
With five types in eleven different sizes offered, Fisher™ 657 and 667 Diaphragm Actuators are engineered to deliver reliable on-off or throttling operation of automatic control valves for a wide range of applications. Travel stops, spring rates and manual operators are offered for virtually any use involving control valves. These devices have a lengthy performance life, thanks to their durable cast iron and steel composition for enhanced steadiness and protection against corrosion and deformation.
The Fisher™ 657 and 667 are used to orient the valve plug in the valve as a reaction to fluctuating controller or valve positioner pneumatic output signals applied to the actuator diaphragm. The compression of the actuator spring dictates the zero setting for these spring-opposed diaphragm actuators, while the actuator spring rate and the amount of available springs dictate span.
With elevated product specifications, operation in cold temperatures (to -50C (-58F)) is possible. (Positioner suggested for optimal functionality when used in temperatures below -40C (-40F).) The Fisher™ 657 and 667 feature a molded diaphragm for optimal thrust, specific to diaphragm size, which travels in a deep casing to limit area change during transport. Reaction time is reduced due to the pressure side’s superficial casing, designed to lessen volume on that side.
The direct-acting 657 and reverse acting 667 offer streamlined mounting. A steady transfer of motion is achieved by a split block stem connection; the lack of linkages safeguards against valve positioning errors and motion loss.