JLG 740AJ Service Manual - Manual (Page 208)

SECTION 3 - CHASSIS & TURNTABLE
3-156 – JLG Lift – 3121160
Minimum Pressure Valve/Check Valve
Assembly
This combined valve located in the filter support housing
has two functions.
The Minimum Pressure Valve - will maintain a pressure of
approximately 65 psig (4.5 bar) in the compressor unit to
ensure oil injection during load conditions and also to
maintain effective oil separation. Once this internal pres-
sure is exceeded it will allow air to discharge downstream
to the service outlet.
The Discharge Check Valve - prevents air in service lines
or downstream receiver from venting down through the
compressor during unload (when the compressor auto-
matically will unload to approximately 40 psig [2.75 bar]
internally) and also during shutdown.
Hydraulic Drive System
Scope of supply may vary depending upon customer
specifications.
Hydraulic pump, oil reservoir, return line oil filter and
hoses to and from the completed packaged compressor
are not furnished with the compressor. This is customer
responsibility.
The packaged compressor unit will normally contain the
hydraulic motor, hydraulic pressure relief valve, and on/off
solenoid valve.
Input hydraulic oil pressure feed is connected to the bulk-
head provided on the compressor package. Within the
package the high pressure oil feeds to a manifold contain-
ing the pressure relief valve and directional solenoid valve.
If a malfunction in the hydraulic motor/compressor assem-
bly causes the hydraulic pressure to rise it will bypass to
the return line to safeguard damage or potential injury.
The directional solenoid valve is normally activated by the
on/off selector switch mounted in the instrument cluster
on the package, this valve is also connected through the
compressor safety circuits for over-temperature and over-
pressure, if either condition occurs it will shut the unit
down, by diverting oil back to tank. It is possible to add
remote on/off switch in parallel with the instrument cluster
to permit on/off operation from another location on the
vehicle.
Hydraulic oil from the manifold is hosed directly to the
hydraulic motor and the outlet from the motor passes to
the return line connection on the package. Customer to
provide both hydraulic feed and return lines.
The hydraulic motor powers the compressor through a
belt drive system.
Compressor Cooling System
The package contains a cooler assembly powered by a 12
volt D.C. electric fan. Oil from the compressor sump
passes through this cooler before being filtered for re-
injection into the compressor. A thermostatic fan tempera-
ture switch activates the fan to come on/off to maintain the
correct operating temperature for the compressor oil. This
switch will activate the fan to come on at approximately
185°F (85°C) and will switch off again at approximately
165°F (74°C). The purpose of maintaining an elevated
temperature during operation is to keep intake air mois-
ture in suspension as it passes through the compressor.
Thermal switch activation is affected by ambient condi-
tions, load/unload cycles (or low oil level).
Initial Startup
The following procedure should be used to make the
initial start-up of your compressor:
1. Position the compressor on a level surface so that
the proper amounts of oil can be added if required.
2. Unit should be bolted down, do not rely on hoses to
hold the module in position.
3. Check all hose connections are tight and wiring con-
nections correct and tight.
4. Check compressor oil level, top up if necessary.
5. Switch instrument panel to OFF.
6. Ensure hydraulic oil to pump inlet. (Prime if neces-
sary)
7. Engage hydraulic system and allow hydraulic oil to
circulate back to tank. Check for leaks.
8. Service valve on compressor closed.
9. Switch the instrument panel switch to ON, this
should very quickly pass oil to the hydraulic motor
on the compressor and start producing air.
10. Check pressure and temperature gauges. Pressure
switch may need adjustment to achieve desired
operating pressure.
11. Partly open service valve to load compressor and
allow to warm up. Monitor temperature gauge, the
ideal operating temperature should be between
165°F and 190°F (74°C and 88°C) although it may be
higher in high ambient conditions.
12. Cycle compressor on/off with service valve to ensure
operation is OK
13. Close service valve then switch instrument switch to
OFF.
14. Disengage hydraulic system.