Figure 34-29. Hydraulic-Power Booster.
Section VIII. AIRBRAKE SYSTEM
as 100 psi. All brakes on a vehicle, and on a trailer when
34-38. Pneumatic Principle. Unlike liquids, gases are
one Is used, are operated together by means of special
compressed easily. If a gas, such as air, Is continued
and a force applied to it, it is compressed and has less
volume. Such a force can be exerted by placing a weight
b. Fundamental Units. A diagram of a typical airbrake
on a piston that fits into a container. The air that originally
braking, because operating air pressure can be as high
filled the entire container is pressed into only a portion of
system used on a motor vehicle is shown in figure 34-31.
the container, due to the force of the weight upon it (fig.
The fundamental units and their functions are described
34-30). The pressure of the compressed air, resulting
in paragraph 34-39.
from the force exerted upon it by the weight, will be
distributed equally in all directions just as it is in a liquid.
Compressed air under pressure may be stored
conveniently and made available for the power
application of brakes.
a. Essential Action. An air pump or compressor driven
by the engine Is used to compress air and force it into a
reservoir, where it is forced under pressure and made
available for operating the brakes. Air under pressure in
the reservoir is released to the brake lines by an air valve
operated by the brake pedal. This released air goes to
brake chambers (located close to the wheel brakes),
which contain a flexible diaphragm. Against this
diaphragm is a plate that is connected directly to the
mechanism on the wheel brakes by linkage. The force of
the compressed air admitted to the chamber causes the
diaphragm to move the plate and operate the brake
shoes through the linkage. Considerable force Is
Figure 34-30. Pneumatic Principle.