Air pressure holds the valve open against a spring, so it is also called air-to-open. Fuel gas supplies, feed valves and emergency shutdown valves are almost always fail-closed, because shutting off energy or inventory is the safe state. On a P&ID it is marked FC, and on a single-acting rotary actuator the way the spring pack is fitted sets the fail direction.
Burner fuel valve is fail-closed, so isolate the air to that positioner and you'll trip the burner.
Read the fail action off the actuator nameplate and spring direction, not off memory; a reversed actuator after rebuild is a classic startup surprise.
Also heard as
- FC
- air-to-open
- ATO
Related terms
Fail-open
Describes a valve whose actuator drives it fully open when air, power or signal is lost.
Spring-return
Describes a single-acting actuator that uses air to move one way and a spring to move back and fail safe.
Solenoid valve
An electrically operated valve in which a coil pulls a plunger to open or close an orifice.
Actuator
The powered device that opens, closes or positions a valve using air, hydraulic oil or an electric motor.