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Instruments and Controls 85
P & Q — Front and Rear Brake System Air Pressures
The system air gauges are directly con-
nected to the front and rear circuit tanks.
The two gauges should register equal air
pressure. Air brake system pressure should
be between 90 to 135 psi (620 to 930 kPa)
for normal operation. The pointers in the
two gauges should register equal air pres-
sure. By observing the gauge pointers, the
operator can detect a pressure drop if an air
leak develops and can readily identify the
circuit affected. See page 224 for more in-
formation.
There is a low-air warning switch in each
gauge. If the pressure in a brake circuit air
tank drops below approximately 60 psi
(420 kPa), the red indicator in the lower
right corner of the gauge will light up and
the master warning indicator and the buzzer
will simultaneously come on. If the air
pressure is allowed to drop below 30 to 40
psi (205 to 275 kPa) in both systems, the
parking brakes will automatically engage to
stop the vehicle. Refer to page 224 for
more information about the brakes.
Failure to observe these precautions can
result in the loss of braking performance
and personal injury or death can occur
as a result of a vehicle crash.
W3003637
W3000638
Master Warning Indicator