Air Brake, a device for stopping cars by operating the brakes by compressed air. The principal features of this system are the air pump, installed on the locomotive just in front of the cab; the main reservoir, in which the compressed air is stored; the engineer's valve in the engine cab, by which all the operations of the air brake are controlled; the train pipe, or principal service pipe, which supplies the auxiliary air reservoirs under each car with compressed air; the triple valve, which serves to feed the compressed air into the auxiliary reservoirs and to supply the brake cylinder with air. It is this triple valve which makes the system automatic. The air, compressed by the air pump, is led through a pipe to the main storage tank. From this air tank, a pipe leads to the engineer's valve in the engine cab, within easy reach of the engine driver. The air generally is compressed to a pressure of 90 pounds to the square inch in the main reservoir. A certain movement of the handle of the engineer's valve opens the ports which permit the air to pass into the train pipe, which runs from the locomotive under each car. This pipe is connected between the cars by a rubber hose, so that it is continuous. When the engineer wishes to apply the brakes, he throws the handle of the engineer's valve to a certain position. That opens a port which permits the air in the train pipe to escape into the open air. This lowers the pressure in the train pipe, and the balanced valve, responding to the higher pressure in the car reservoir, slides back, and thus opens an aperture which permits the air in the car reservoir to reach the brake cylinder. The pressure of the air forces the piston of the brake cylinder forward, and this piston, through suitable levers, presses the brake shoes against the wheels and the brakes are set. Within the brake cylinder is a coiled spring. When the engineer desires to release the brakes, he feeds air from the main reservoir on the locomotive into the train pipe, thus increasing the pressure. This forces the balanced valve the other way, and thus opens an aperture which releases the air in the brake cylinder into the open air. The coiled spring, reacting, forces the brake piston back to its normal condition, and thus releases the brakes. The air brakes used on electric cars operate on the same principle, but are of simpler construction. The pump for compressing the air is operated by an electric motor which obtains its current from the wire that supplies the car motor. The air brake was developed by George Westinghouse,(1846-1914), American inventor, engineer, and industrialist. Although successfully demonstrated in 1868, the air brake did not become standard equipment until after the passage of the Railroad Safety Appliance Act in 1893. See AIR; AIR COMPRESSOR; COMPRESSED AIR.