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air brake:see brakebrake,
in technology, device to slow or stop the motion of a mechanism or vehicle. Types
Friction brakes, the most common kind, operate on the principle that friction can be used to convert the mechanical energy of a moving object into
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air brake[′er ‚brāk]
A friction type of energy-conversion mechanism used to retard, stop, or hold a vehicle or other moving element. The activating force is applied by a difference in air pressure. With an air brake, a slight effort by the operator can quickly apply full braking force. See Friction
The air brake, operated by compressed air, is used in buses; heavy-duty trucks, tractors, and trailers; and off-road equipment. The air brake is required by law on locomotives and railroad cars. The wheel-brake mechanism is usually either a drum or a disk brake. The choice of an air brake instead of a mechanical, hydraulic, or electrical brake depends partly on the availability of an air supply and the method of brake control.
In a motor vehicle, the air-brake system consists of three subsystems: the air-supply, air-delivery, and parking/emergency systems. The air-supply system includes the compressor, reservoirs, governor, pressure gage, low-pressure indicator, and safety valve. The engine-driven compressor takes in air and compresses it for use by the brakes and other air-operated components. The compressor is controlled by a governor that maintains air compression within a preselected range. The compressed air is stored in reservoirs. The air-delivery system includes a foot-operated brake valve, one or more relay valves, the quick-release valve, and the brake chambers. The system delivers compressed air from the air reservoirs to the brake chambers, while controlling the pressure of the air. The amount of braking is thereby regulated. In the brake chambers, the air pressure is converted into a mechanical force to apply the brakes. As the pressure increases in each brake chamber, movement of the diaphragm pushrod forces the friction element against the rotating surface to provide braking. When the driver releases the brake valve, the quick-release valve and the relay valve release the compressed air from the brake chambers. The parking/emergency system includes a parking-brake control valve and spring brake chambers. These chambers contain a strong spring to mechanically apply the brakes (if the brakes are properly adjusted) when air pressure is not available. During normal vehicle operation, the spring is held compressed by system air pressure acting on a diaphragm. For emergency stopping, the air-brake system is split into a front brake system and a rear brake system. If air pressure is lost in the front brake system, the rear brake system will continue to operate. However, the supply air will be depleted after several brake applications. Loss of air pressure in the rear brake system makes the front brake system responsible for stopping the vehicle, until the supply air is depleted.