Lockout open and no pilot signal. Inlet air is blocked by inlet poppet C. Any down stream pressure forces sliding piston B upward. This opens the exhaust port and vents the downstream air.

Lockout open and pilot signal applied. Pilot air forces piston B down ward to close exhaust port. Pilot air also flows past the me tering 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. Inlet air now flows freely to the outlet port.

Lockout closed. At any time the lockout handle can be pushed inward, closing off the flow of pilot air. Pilot air above pistons A and B is then vented through the exhaust port. Piston A moves upward closing inlet poppet C. Sliding piston B moves upward opening the exhaust port and venting the downstream line.