These pictures show some parts of an air clamping system. The pictures are described below:
Air clamp switch 1: Shows a close up of the switch mounted above the quill stop on a Bridgeport.
Air clamp switch 2: Shows the same switch setup but not so close.
Air clamp 1: Shows a couple clamps that swing down to clamp.
Air clamp 2; Shows a 3C air collet closer.
Air clamp valve: shows the solenoid valve mounted to a box which contains a step down 
transformer and some related electrics for the solenoid.
The box in turn is mounted to the wall behind the mill.
The whole setup works like so: The mill mounted switch turns ON the solenoid which operates
the valve. The air lines are connected such that turning ON the solenoid unclamps the
air clamps. That way a loss of power keeps the clamps tight. I use push in air fittings
and stiff nylon air lines so I can change clamping mechanism quickly without tools. Quick
disconnect air fittings are more expensive and more likely to leak a little than the push
to connect air fittings.