SECTION 4 - HYDRAULICS
4-26 – JLG Lift – 3121642
8. Disable the engine to prevent it from starting. Crank the
starter for several seconds. Do not exceed the engine
manufacturer’s recommendation. Wait 30 seconds and
then crank the engine a second time as stated above.
This operation helps remove air from the system lines.
Refill the reservoir to recommended full oil level.
9. When the gauge begins to register charge pressure,
enable and start engine. Let the engine run for a mini-
mum of 30 seconds at low idle to allow the air to work
itself out of the system. Check for leaks at all line connec-
tions and listen for cavitation. Check for proper fluid
level in reservoir.
10. When adequate charge pressure is established (as
shown in model code), increase engine speed to normal
operating rpm to further purge residual air from the sys-
tem.
11. Shut off engine. Connect pump control signal. Start
engine, checking to be certain pump remains in neutral.
Run engine at normal operating speed and carefully
check for forward and reverse control operation.
12. Continue to cycle between forward and reverse for at
least five minutes to bleed all air and flush system con-
taminants out of loop.
NOTE: Normal charge pressure fluctuation may occur during for-
ward and reverse operation.
13. Check that the reservoir is full. Remove charge pressure
gauge. The pump is now ready for operation.
Removing the pump
CONTAMINATION CAN DAMAGE INTERNAL COMPONENTS AND VOID THE MAN-
UFACTURER’S WARRANTY.
TAKE PRECAUTIONS TO ENSURE SYSTEM CLEANLINESS WHEN REMOVING AND
INSTALLING SYSTEM LINES.
DISASSEMBLY:
1. With the prime mover off, thoroughly clean all dirt and
grime from the outside of the pump.
2. Tag, disconnect, and cap each hydraulic line connected
to the pump. As hydraulic lines are disconnected, plug
each open port, to ensure that dirt and contamination
do not get into the pump.
3. Remove the pump and its auxiliary pump (if applicable)
as a single unit.
NOTE: Be careful, do not damage solenoids and electrical connec-
tions when using straps or chains to support the pump.
INSPECTION:
4. Ensure the work surface and surrounding area are clean
and free of contaminants such as dirt and grime.
5. Inspect the system for contamination.
6. Look at the hydraulic fluid for signs of system contami-
nation, oil discoloration, foam in the oil, sludge, or metal
particles.
REASSEMBLY:
7. Before replacing the pump, replace all filters and drain
the hydraulic system. Flush the system lines and fill the
reservoir with the correct, filtered hydraulic fluid.
8. Fill the pump with clean, filtered hydraulic fluid.
9. Attach the pump to the prime mover. Torque mounting
screws according to the manufacturers recommenda-
tion.
10. Replace all hydraulic lines. Ensure the charge inlet line is
filled with fluid.
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