AIR BRAKES
Air brakes use compressed air supplied by a machine called a compressor. Most buses, heavy trucks, and trains have air brakes. When the driver or engineer applies the brakes, a storage unit releases compressed air. The air pushes against a piston or diaphragm, which applies brake pressure to pads or shoes. Buses and trucks have disc and drum brakes like those in cars. In trains, however, shoes press against the outside of the wheel.
