Spring-return Actuators

Spring-return actuators are spring opposed pneumatic cylinders. A 3-way solenoid valve is used to operate a spring return actuator.

The normal position is the position of the valve with the spring extended and the solenoid de-energised. The available force is the pressure times the area of the piston less the spring force [F=(PxA)-Fs] in one direction and the available spring compression force in the opposite. Spring force is determined by the spring rate (K) times the compression, in inches (F=KxIn) at any given position of stroke. Spring and piston actuators are typically sized for 80psi minimum. Spring and diaphragm actuators for (control valves) should be sized for 35psi (6-30psi signal). Spring return actuators are inherently fail safe. Trip valves are available for lock-in-last-position fail safe action.

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