Theory of Air Brakes
Air brakes (also known as spring brakes) have been around nearly as long as the compressor and automobile. These heavy but reliable systems are used where safety takes priority over weight, and are responsible for keeping more trucks out of more ditches than any development since the drum brake.
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History
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Air brakes as we know them today were patented by George Westinghouse in 1872 for railway use, and were first introduced to road vehicles in 1912.
Purpose
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Since they require an outside force (air pressure) to release, air brakes are considered a "default-on" system. This stands in contrast to the average car's hydraulic (fluid) brakes, which require that a force be exerted to engage them.
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Brake Components
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The axle-mounted brake shoes on an air brake system are held against the wheel-mounted brake drum by a powerful spring. The spring opposes an air chamber, which must be pressurized to move to relieve the spring pressure and disengage the brakes.
Air Pressure
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Because air brakes will not release without air pressure, a vehicle so equipped must idle for several minutes to allow the engine-mounted compressor time to build pressure.
Safety
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If any component of an air brake system fails, the entire system is designed to vent all air pressure and immobilize the vehicle for repairs.
Applications
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In addition to their use on almost all semi trucks and trains, air brakes are also utilized on many buses, trailers and box delivery trucks.
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References
Resources
- Photo Credit Image by Flickr.com, courtesy of Oregon Department of Transportation
