Page 161 - Driving Commercial Vehicles Manual+

driving commercial vehicles

Brake shoe return springs keep the brake linings away from the drum when
the air pressure is released from the air chamber.

The picture on the left
shows the brake linings
mounted on the axle
housing. The brake drum on
the right is mounted on the
wheel and rotates with it.

Compressor

The first requirement of an air brake system is a way to compress air and store
it in reservoirs (tanks) so that it’s available for instant use.
The source of the compressed air is the compressor, which takes in air from
the atmosphere and compresses (pressurizes) it. The compressed air is then
pumped through an air line to a supply reservoir.

A gear-driven compressor
and governor.

The compressor is mounted on the engine of the bus or truck. On most new
driving tip engines, the compressor is mounted on the side of the engine and driven by
gears. A belt, like a fan belt, drives some compressors. As long as the engine
Check belt tension by is running, the compressor will be running.
pressing down on the belt
midway between the pulleys. All trucks use piston-type air compressors. They may have one, two or four
If you can press it in more cylinders depending on the vehicle’s volume demands.
than double the width of the When air is compressed, its temperature rises. With a truck air compressor
belt, the tension needs to be
adjusted. operating at a pressure of 120 p.s.i. (827 kPa), the air temperature as it leaves
the compressor is over 204° C (400° F).

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