SUB-SECTION 9A
AIR SYSTEM
SUB-SECTION 9A
AlR SYSTEM
The relay valve vents air pressure from the rear service
SCOPE
brake chambers locally, making it unnecessary for the air to
travel back through the line to the treadle valve.
The air system of this machine consists of the devices used
to control and actuate the carrier brakes, carrier remote
PARKING BRAKES. By depressing the Maxibrake control
controls when furnished, and the air operated throttle used
knob, on the carrier dashboard, the operator can use the
on later machines.
Maxibrakes as parking brakes. Depressing the Maxibrake
control knob cuts off pressure at the inlet of the exhaust
BRAKE SYSTEM DESCRIPTION
and pressure retaining valve, exhausting air from the spring
chambers of the Maxibrakes. Venting the spring chambers
GENERAL. This machine is equipped with an air brake
allow the power springs to expand and apply the rear wheel
system which serves three separate functions. These func-
brakes.
tions are service brakes, perking brakes and emergency
brakes. The operation of each of these sub-systems is de-
The brake will remain set until air pressure is reapplied to
scribed below (see Figures 9A-1 and QA-2).
the spring chambers, compressing the power springs and
releasing the brakes.
Compressed air for the operation of the brake system is
supplied by an engine driven air compressor, and is stored
Pulling out the Maxibrake control knob applies air pressure
in a number of tanks on the machine. A governor, mounted
to the inlet of the exhaust and pressure retaining valve,
on the air compressor, senses the pressure of the air in the
closing off the exhaust port of the valve. Air pressure then
tanks, and controls the compressor output. Compression
passes through the movable seat of the valve, and into the
starts when the pressure drops to approximately 105 psi
spring chamber. This compresses the power springs, re-
(7.24 BARS) and is stopped by the governor when it
leasing the brakes.
reaches approximately 120 psi (8.27 BARS).
EMERGENCY BRAKES. The basic Purpose of the Maxi-
SERVICE BRAKES. Supply air from the tanks is available
brakes is to provide a means of stopping the vehicle in the
at the brake treadle valve at all times. When the operator
event that air pressure is lost or drops below a safe level
depresses the brake treadle, air from the dry tank passes
when the vehicle is in motior..
through the treadle valve to the relay end quick release
valves, which admits air from the tank to the front and rear
The Maxibrake control valve functions autometically as
service brake chambers. Air pressure in the brake chambers
well as manually. In the event that air pressure drops to 28
force the brake shoes apart, placing them in contact with
the brake drums, and braking force is applied to the wharfs.
psi (1.93 BARS) or lees, pressure at the inlet port of the
Inasmuch as the air pressure deliverad to the brake cham-
control valve will be overcome by the force applied to the
bars is controlled by the treadle valve, the driver, by oper-
valve shuttle by the spring, and the spring will shift the
ating the treadle valve end controlling the air pressure da-
shuttle to the applied Position. This will vent air Pressure
livered to the brake chambers, also controls the braking
from the inlet of the exhaust and pressure retaining valve,
force being developed.
thus venting air pressure from the spring chambers. The rear
brakes will then be applied by the force created by the
power springs.
The relay valve is provided to speed up the application and
release of the rear brakes. The valve operates as a remote
controlled brake valve, delivering air to the rear service
Air pressure to compress the power springs is normally
supplied by the dry tank, through the Maxibrake control
brake chambers which is at the same pressure as the air
which is delivered to the relay valve by the treadle, valve.
valve, to the spring chambers. This arrangement would not
9A-1
