Pulsing the valve ?
 

Whenever you pulse the valve, the piston will move a little. The end with the pressure receives air and the other end forces air out through the exhaust port of the valve to the atmosphere.

Then the valve switches, and the end that just lost the air receives more, and the end previously filling with air, now exhausts it to the atmosphere.

The cycle above repeats. But since the pressurized air all has to come from the compressor and the reservoir, the compressor would be on all the time.

also, pneumatics extend faster than they retract. (More surface area on the extension.)