Operator`s manual

MAINTENANCE MANUAL
SECTION 7
7. PNEUMATIC SYSTEM
7.1 GENERAL
For numbered references of the Pneumatic Diagram, refer to Figure 7-1.
Air is provided by the engine air compressor through the Air Compressor Governor (9) to the Air Pressure
Regulator (6). The engine air compressor operates whenever the engine is running. If the Engine Throttle
Solenoid Valve (5) is closed, the air pressure will recirculate through the air compressor. When the
Engine Throttle Solenoid Valve is opened, by actuating one of the remote Engine Throttle Controls, air
pressure is allowed to build up in the system. When the pressure in the lines and in the Air Tank (2)
arrives at the pressure set on the Regulator pump (6), air is once again recirculated through the air
compressor. For a description of the operation of the Engine Air Compressor, refer to Part 2, Volume 2,
"Detroit Diesel Engine V-71 Highway Vehicle Service Manual, Section 12.4".
When the PTO Control Valve (1), located in the cab, is switched to "ENGAGE", air pressure is transferred
to the PTO Shift (7) and to the Ladder Bed Lock (4). Air pressure then causes the PTO to be engaged
with the engine and causes the piston in the Ladder Bed Lock to move and withdraw the locking arms
from the ladder rails. When the PTO shift switch is switched to "DISENGAGE", air pressure stored in the
Air Tank is allowed to activate the PTO Shift and disengage it from the engine. At the same time, it moves
the Ladder Bed Lock Piston in the opposite direction to re-engage the locking arms on the ladder rails.
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