Solenoid not energized. Inlet air is blocked by pop pet C. Piston B slides on the valve stem and is pushed up ward if there is any down stream pressure. This opens the exhaust and vents the down stream line.

Solenoid energized. Pilot air forces piston B down ward to close exhaust port. Pilot air also flows past the metering pin, opens the ball check, and slowly pressurizes the outlet line. Pres sure is also building up on piston A.

When the pressure on piston A reaches 50% of inlet pressure, the piston is forced downward, opening inlet poppet C. Full inlet pressure now flows freely to the outlet port.

Solenoid de-energized. Air above pistons A and B is exhausted through the exhaust port of the pilot valve. Air above poppet C forces sliding piston B up so that the main exhaust port is opened and pressurized air is exhausted.