[Al Skierkiewicz]

There is no way to control the position of a pneumatic cylinder without mechanical stops. Once air enters the cylinder, the piston will move based on the air pressure and the force it is trying to move. If it can overcome the force it is trying to move, it will move until it comes to the end of it's travel (a mechanical stop inside the cylinder). You can control the speed at which the cylinder is moved by using flow control valves at the ports of the cylinder. There is a tradeoff in the time it takes to travel.