As shown in Figure 1, it has three ports P, A, T ,, P then air source, A connected to the implementation of components, T through the atmosphere. When P has compressed air input, push the spool to the right, P and A pass to the actuator supply; when P without compressed air input, the gas in the actuator through A to make the valve spool to the left to block the P, A channel, while opening A, T channel, T quickly exhaust gas. Quick exhaust valve is usually installed between the reversing valve and the cylinder, so that the cylinder exhaust without the rapid discharge through the valve. Thus speeding up the cylinder reciprocating speed, shorten the work cycle.