Air pressure compresses the spring to stroke the valve, and the spring stores the energy to return it when air vents. That gives a known fail position without accumulators, which is why shutdown valves favour spring-return units. The tradeoff is size: the actuator must overcome the spring as well as the valve, so it is larger and heavier than a double-acting unit for the same valve.
Spec a spring-return actuator for the ESD valve, double-acting with a volume tank won't pass the safety review.
Also heard as
- single-acting
- spring-to-close
- spring-to-open
Related terms
Double-acting
Describes an actuator that uses air or oil pressure to drive in both directions, with no return spring.
Fail-closed
Describes a valve that springs shut when it loses air, power or its control signal.
Fail-open
Describes a valve whose actuator drives it fully open when air, power or signal is lost.
Actuator
The powered device that opens, closes or positions a valve using air, hydraulic oil or an electric motor.