Once the air supply for the circuit is turned on, the actuation of a selector switch is to cause the pneumatic piston to extend gradually. Once the piston touches the 3/2 way roller lever valve, the piston is to retract quickly. Once the piston touches the roller valve closest to the cylinder, the piston extends again and continues the cycle until the selector switch is reset. The gradually extension and the quick retraction of the pneumatic piston is controlled by two different one-way flow control valve. When the emergency pushbutton is pressed, the piston stops instantly, no matter its position.
![](https://i.ytimg.com/vi/mGq056gv0lw/maxresdefault.jpg)