Another Option for Controlling Actuator Speed

Another option we have for controlling the speed of the return stroke of a cylinder would be by using a quick exhaust valve. A quick exhaust valve, when attached on the return stroke side of a cylinder, will allow the evacuating air to exhaust to the atmosphere immediately without having to return to the valve and then exhaust through an exhaust port.

Below is an example of a quick exhaust valve. The port on the right is incoming pressure from the valve. The port on the left is attached as closely as possible to the non-rod side of a cylinder, and the port on the top is where the evacuating air from the cylinder is exhausted into the atmosphere when the cylinder is retracting.

The following schematic shows how the insides of a quick exhaust valve work.

Parker Hannifin Corporation. (1980). Industrial Pneumatic Technology. Parker Hannifin Corp. DOI: 1557690154

Port #1 aligns with the right side of the picture above. Air enters from the control valve and flows through the quick exhaust port to Port #3 and extends the cylinder. When the cylinder is retracted, air comes in the quick exhaust port from Port #3. However, it can't exit Port #1 because of the check valve. It must then exit Port #2 and vent to the atmosphere.

Why Do They Speed up the Process?

Quick exhaust ports speed up the process of retracting the cylinder because the air does not have to travel far to exhaust. Remember, the speed of an actuator is dependent on overcoming system frictional pressure. If the air on the exhaust side of a cylinder does not have to travel through a hose and through a valve to exhaust, the retract stroke of the cylinder will become quicker, which, in turn, can speed up the production cycle of a machine.

Trainer Lab #11 will demonstrate how a quick exhaust valve works.

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