[Doc Wu]

No, that's not how pneumatics work. Even if you shut off the air supply at the solenoid, the air trapped will continue to expand. The only thing that stops a pneumatic cylinder is a physical stop: the end of the cylinder or a mechanical limit.

There is a common misconception that switches, or any sensor, 'stop' machinery. I used to get this in my profession all the time, even from engineers. Sensors do not stop anything. They do not have magical powers. All they do is report on the condition they were installed for. They are feedback, not action. I've seen many expensive electronic switches destroyed in machinery because someone designed them to stop the travel of a mechanical piece and put them in the path of that piece.

Also, it's a REED switch. If you ever opened one up, or looked at a bare one, you'd know why. Two thin, flat ferrous metal blades are trapped in a glass tube with the ends overlapping, but not quite touching. When a surrounding magnetic field induces a magnetic field in the blades, they attract to each other and close the gap. Simple and effective.