Air brakes or more formally a compressed air brake system is a type of friction brake for vehicles in which compressed air pressing on a piston is used to apply the pressure to the brake pad
needed to stop the vehicle. Air brakes are used in large heavy
vehicles, particularly those having multiple trailers which must be
linked into the brake system, such as trucks, buses, trailers, and semi-trailers in addition to their use in railroad trains.
George Westinghouse first developed air brakes for use in railway
service. He patented a safer air brake on March 5, 1872. Westinghouse
made numerous alterations to improve his air pressured brake invention,
which led to various forms of the automatic brake. In the early 20th
century, after its advantages were proven in railway use, it was adopted
by manufacturers of trucks and heavy road vehicles.The air compressor is driven by the engine either by crankshaft pulley via a belt
or directly from the engine timing gears. It is lubricated and cooled
by the engine lubrication and cooling systems. Compressed air is first
routed through a cooling coil and into an air dryer which removes moisture and oil impurities and also may include a pressure regulator, safety valve and a smaller purge reservoir.
As an alternative to the air dryer, the supply system can be equipped with an anti freeze device and oil separator. The compressed air is then stored in a reservoir
(also called a wet tank) from which it is then distributed via a four
way protection valve into the front and rear brake circuit air
reservoir, a parking brake reservoir and an auxiliary air supply
distribution point. The system also includes various check, pressure limiting, drain and safety valves.
