AIR SYSTEM
SUB-SECTlON 9A
method of checking the serviceability of the system must
provide a means of moving the vehicle from the point at
be employed to be sure that all parts of the system are
which it was stopped by the Maxibrakes, if the loss of air
pressure is due to a failure in an air line or the compressor.
inspected. The procedure outlined below is one such
method.
Therefore, an emergency air tank, which is isolated from
the service air system by a check valve, is provided.
Since the emergency air tank is isolated from the service air
system, air pressure will be available in the emergency tank
to release the Maxibrakes. To release the Maxibrakes, after
Do not use the brake system to hold the machine
an air system failure. the operator would depress the emer-
while performing the following test. Hold the ma-
gency release valve knob and pull out the Maxibrake con-
chine by blocking the wheels with wheel chocks.
trol knob. This applies air pressure from the emergency
tank to the spring chambers. through the Maxibrake control
1. Drain Air Tanks. Charge the air brake system. Open the
valve and the exhaust and pressure retaining valve. This
drain cocks on each air tank. Close the drain cocks after all
compresses the power springs. releasing the brakes.
devices have been completely drained of all air pressure and
CARRIER REMOTE CONTROL DESCRIPTION
2. Check Stop Light Switch. With no air pressure in the
system, start the engine, depress the brake pedal, and ob-
The carrier remote controls operate the carrier steering
serve the dash gauge pressure when the stop lights light up.
system, clutch and transmission, and the service brakes by
Stop lights should normally light when the dash gauge regis-
means of air valves and cylinders.
ters approximately 5 pounds (0.34 BARS). Release the
Depressing a pushbutton on the carrier remote control
brake pedal and the stop light should go out.
panel, completes an electrical circuit which energizes a sole-
noid operated air valve. When on air valve is operated, it will
3. Check Brake Chamber Push Rod Travel. Apply the
allow air to pass through it to an air cylinder which will
brakes and check the push rod travel of each rear brake.
operate the desired actuator. When the air valve is de-
Adjust if the stroke is excessive.
energized. by releasing the pushbutton, air pressure will be
blocked, and the air in the cylinder will be vented to atmos-
4. Check Low Air Pressure Light. Run engine, continuing
phere.
pressure build-up Low pressure light must remain lit until
dash gauge pressure reaches approximately 60 pounds (4.13
AIR THROTTLE DESCRIPTION
BARS), at which point the light should go out.
Later machines are equipped with an air operated throttle
5. Pressure Build-Up Test. Run engine at fast idle. Time
in both the upper and carrier. Air from the air compressor
required to raise the air pressure from 50 to 90 pounds (3.44
IS supplied to the selector valve in the carrier cab which
- 6.20 BARS) will vary, but should not exceed 5 minutes.
directs the air to either the carrier air tank or the upper air
6. Governor Setting Test. Run engine. Governor should cut
tank,
out, stopping further compression, at approximately 120
pounds (8.27 BARS). Reduce air pressure by making a series
When the throttle pedal in either the carrier or upper cab is
of brake applications. The governor should cut in, resuming
depressed, air pressure from the appropriate tank is supplied
compression, at approximately 105 pounds (7.24 BARS).
to the slave cylinder on the engine through the shuttle valve.
Air pressure at the slave cylinder moves the engine throttle
7. Leakage Test. Run the engine until the governor cuts
in the appropriate direction to increase engine speed.
out. Stop the engine. Wait until the air pressure stabilizes.
With the brakes released, dash gauge pressure drop should
Allowing the throttle pedal to return to the released posi-
tion will vent air pressure from the slave cylinder, which
not exceed 2 pounds per minute (0.13 BAR/min). Make a
moves the engine throttle in the appropriate direction to
full brake application and hold it. Allow the pressure to
decrease engine speed.
stabilize. Pressure drop should not exceed 3 pounds par
minute (0.20 BAR/min). Check system connections and
TESTING FOR SERVICEABILITY
applicable devices if leakage in either test is excessive.
To ensure that the brake system is functioning properly,
8. Operating Tests. Connect an accurate test gauge to the
and to aid in scheduling brake system service, a systematic
brake valve delivery line. Fully charge the air brake system.
9A-2
