Troubleshooting guide

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This aspect of brake fundamentals is not often
considered in evaluating brake performance, particularly
when different forms of brakes are involved. A common
method of testing brakes is through the use of
a decelerometer – a device that determines the
maximum rate of deceleration developed during
a stop. A decelerometer shows a calculated stopping
distance from a speed of 20 miles per hour, based on the
maximum rate of deceleration developed during a stop.
Such instruments do not, however, make allowances for
lost time before the braking system develops full power.
Therefore, they are not suitable for analyzing time lag
factors in brake performance.
In terms of stopping time or distance, true
performance of any brake system can be determined
only one way – by measuring the time and distance
the vehicle travels from the instant the driver
depresses the brake pedal to the point where the
vehicle stops. Such tests can be made comparative only
by using instruments to accurately determine the speed
of the vehicle at the instant the brake pedal is depressed.
The Fundamentals of Compressed Air
Compressed air is air that has been forced into a space
smaller than it would ordinarily occupy in its free or
atmospheric state.
Free air that we breathe – or atmosphere – is normally
always under pressure because of the weight of the
air above it. This pressure amounts to 14.7 pounds per
square inch at sea level, and it decreases as the altitude
increases.
The normal atmospheric pressure of 14.7 pounds per
square inch is usually ignored and the atmosphere is
considered to be free air under no pressure. This is the
reason air pressure gauges register zero when connected
only to atmosphere. The pressure of compressed air
is commonly indicated as the amount of pressure, in
pounds per square inch, above the atmosphere.
FIGURE 8 - FREE SPRING / FREE AIR
FIGURE 9 - COMPRESSED SPRING / COMPRESSED AIR
FIGURE 10 - FREE SPRING / FREE AIR
FIGURE 11 - FREE SPRING / FREE AIR
Properties of Compressed Air