JLG 740A, Service And Maintenance Manual

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SECTION 3 - CHASSIS & TURNTABLE
3121160 – JLG Lift – 3-161
Intake Control
The intake control consists of two main sub-assemblies:
1. Inlet Valve Assembly: The inlet valve opening/clos-
ing (load/unload) is controlled by admitting/exhaust-
ing pilot air pressure through the solenoid valve to
the piston which is part of the inlet valve assembly.
The inlet valve is not a routine maintenance item.
Maintenance kits are available which include
replacement seals, etc.
2. Solenoid Valve: Attaches directly to the inlet valve
and responds to signals from the pressure switch to
admit/vent pilot air pressure to the inlet valve to con-
trol load/unload. In the unlikely event of failure this
item is to be replaced as a complete item.
Minimum Pressure Valve
Normally factory set to 65 psig (4.5 Bar). Provides two
main functions:
1. Maintains Minimum Pressure: Prevents down-
stream air to pass until compressor system is up to
minimum pressure valve setting which aids in main-
taining good oil supply to the compressor and also
is a requirement for good oil separation.
2. Back Pressure Check Valve: Allows for compres-
sor to be unloaded to lower pressure than supply air
line system and permits compressor air pressure to
be totally relieved when stopped.
This valve is not a routine maintenance item. Seals
and replacement parts are available.
Compressor Thermal Valve
Controls compressor oil temperature and permits for rapid
compressor oil warm up. Commences to pass oil through
cooler at 160°F (71°C) and is fully open at 185°F (85°C).
Safety Shutdown Systems
Protection for over-pressure and/or over-temperature is
provided. If either condition should occur the diverter
valve should activate to divert hydraulic fluid back to tank
and the compressor will stop, the reset on instrument
panel will pop out and stay out until reset. Reason for
shutdown should be investigated before pressing reset.
Periodically (every 6 months or every 500 hours) the shut-
down system should be tested as follows: Compressor
operating, close service valve and allow compressor to
unload (2 minutes or more) then touch across button on
gauge face to Bezel surrounding the respective gauge
with coin or screwdriver. Reset button should pop out and
compressor stop. Switch off compressor and press reset
button to reactive shutdown system.
Troubleshooting
The information contained in the Troubleshooting Chart
has been compiled from information gathered. It contains
symptoms and usual causes for the most common types
or problem. All available data concerning the trouble
should be systematically analyzed before undertaking any
repairs or component replacement.
A visual inspection is worth performing for almost all prob-
lems and may avoid unnecessary additional damage to
the machine. The procedures which can be performed in
the least amount of time and with the least amount of
removal or disassembly of parts should be performed first.
BEFORE WORKING ON ANY MACHINE, ENSURE IT IS SHUT
DOWN AND ISOLATED, AIR PRESSURE RELIEVED, AND UNIT
HAS COOLED DOWN.