Pneumatic Quick Exhaust Valve

A quick exhaust valve has three ports: supply from the directional valve, a cylinder port, and a large exhaust port open to atmosphere. While the directional valve is feeding, the internal element is pushed across so supply passes to the cylinder and the exhaust port is closed. When the directional valve switches and the supply line drops, the element moves back, the supply path closes and the cylinder port opens straight to the exhaust.

The gain is speed. Air leaving the cylinder no longer has to travel back along the connecting tube and through the restricted passages of the directional valve; it dumps locally through a short, large opening. On a long tube run or a small directional valve this can cut return-stroke time substantially, and it is the standard fix when a cylinder extends briskly but retracts slowly.

The valve is fitted as close to the cylinder port as possible, usually screwed directly into it, because any tube left between the valve and the cylinder still has to be emptied through the connecting line and gives back the benefit. The exhaust port is normally fitted with a silencer, both to cut noise and to keep dirt out of the valve; a silencer that clogs will slow the valve down again, so it is a maintenance item.

When ordering, specify the port size and thread form, and check the direction of fitting - supply, cylinder and exhaust are not interchangeable. A quick exhaust valve should not be combined with a flow control valve on the same cylinder port without thinking it through, since one is fitted to speed the exhaust up and the other to slow it down.