The spring return pneumatic actuators use an air supply to drive the valve stem in one direction and an internally loaded spring to return to the valve to its original position.

When the coil power, the pilot valve by the spring return, pilot hole open, pressure relief valve on the chamber, the piston on the lower chamber medium pressure to promote the solenoid valve open.

Normally Open: When the coil is energized, the pilot hole closed, the valve chamber and pressurized by the piston return spring throttle thrust, the electromagnetic valve is closed.