How Does
How Trailer Air Brakes Work
Compressed Air System
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Compressing air for application in a trailer air brake system begins with a compressor, which is attached to the truck's engine. The compressor is regulated by a governor. The governor automatically starts the compressor when the air pressure in the trailer air brake system is reduced to 100 psi. This restores the air pressure, and the governor turns off the air compressor at 125 psi.
Compressed air is stored in air tanks. The size and number of air tanks varies from truck to truck and are based on the intended use of the truck. More tanks are necessary when the truck carries heavier than normal loads or when used primarily in congested traffic. All compressed air tank installations are designed to allow use of the trailer brakes several times in case of compressor failure.
Trailer Brakes
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Brake shoes for trailers come in three types. The most common is the S-cam, followed by disc brakes. The S-cam brake derives its name from the design of the cam shaft that moves brake shoes toward or away from the inside of the wheel's hub. As air pressure is increased in a trailer brake, a push rod turns the S-cam shaft to cause the brake shoes to move away from the wheel hubs.
The second type of trailer air brakes is a disc brake. Disc brakes use a power screw instead of a S-cam to open and close trailer brakes. When air pressure is applied the power screw turns to move the brake shoe from the rotor on a wheel. The opposite occurs when air is removed, causing the power screw to cause the brake shoe to close against the rotor to slow or stop the trailer.
eHow Article: How Trailer Air Brakes Work
