Pneumatic Logic
From DT Online
Combining valves together allows us to produce logic circuits.
The simplest of these is an AND circuit. By connecting up the valves in series as shown, the cylinder only operates if the first valve AND the second valve are switched on.
Note: Logic circuits can be used to make pneumatic systems safe. For example some pneumatic drills will not work unless a guard is in place. The drill requires two switches to be operated in order to work: the first by putting the guard in place, AND the second by pressing start.
An OR ciruit is produced by combining the outputs of two valves with a shuttle valve.
The shuttle valve is required because if the pipes wire simply connected together, when the first valve was on and the second valve off, compressed air would simply exhaust to the atmosphere through the second valve. With the OR circuit, if either the first valve OR the second valve are switched on, then the cylinder is activated.