MAINTENANCE OF M939 SERIES VEHICLES - OD1661 - LESSON 1/TASK 1
(9)
Wet Tank Reservoir.
Performs two functions:
(a) Traps water in air
to
protect
other
air
systems
from
freezing or corrosive damage.
(b) Stores air, enabling the operator to make normal stops when
the engine stalls or the compressor fails.
(10) Secondary Air System Shutoff Valve.
When closed, the valve
will isolate the secondary system and maintain air pressure to enable
the operator to slow or stop the vehicle.
only.
(11) Spring Brake Chamber.
Contains a large spring which applies
the rear brakes when the spring brake air pressure is released.
(12) Rear Emergency Coupling.
When towing another vehicle, the
coupling allows pressurized air from the brake system to charge the
towed vehicle's brake system.
(13) Rear Service Coupling.
When towing another vehicle, this
coupling is connected to the towed vehicle so that the brake systems
of the two vehicles work together.
(14) Spring Brake Reservoir. Stores enough air pressure to release
the spring brakes for emergency operation in the event of primary or
secondary air system failure.
(15) Pedal Valve. Allows air pressure from the secondary constant
pressure system to flow into the secondary signal system when the
operator depresses the pedal.
(16) Air Compressor.
Draws in air from the intake manifold and
forces it into the brake system.
f.
Lighting System Operation. The lighting system is identical on
all models covered in this lesson and consists of the following major
components.
(1) Service Headlights (figure 9 on the following page). Powered
from the light switch for high beam and low beam requirements.
16
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