JLG 4394RT Service Manual - Manual (Page 175)

SECTION 4 - HYDRAULICS
3121249 – JLG Lift – 4-9
“Jog” or slowly rotate prime mover until charge pressure
starts to rise. Start prime mover and run at the lowest pos-
sible RPM until charge pressure has been established.
Excess air may be bled from high pressure lines through
high pressure gauge ports.
DO NOT START PRIME MOVER UNLESS PUMP IS IN NEUTRAL
POSITION (0 DEGREES SWASHPLATE ANGLE). TAKE PRECAU-
TIONS TO PREVENT MACHINE MOVEMENT IN CASE PUMP IS
ACTUATED DURING INITIAL START-UP.
Once charge pressure has been established, increase
speed to normal operating RPM. Charge pressure should
be approximately 220 psi (15.5 bar) minimum. If charge
pressure is incorrect, shut down and determine cause for
improper pressure.
INADEQUATE CHARGE PRESSURE WILL AFFECT THE OPERA-
TOR’S ABILITY TO CONTROL THE MACHINE.
Shut down prime mover and connect external control
input signal. Start prime mover, checking to ensure pump
remains in neutral. With prime mover at normal operating
speed, slowly check for forward and reverse machine
operation.
Charge pressure should remain at 220 psi to 240 psi (15.5
bar to 16.9 bar) minimum during forward or reverse opera-
tion. Continue to cycle slowly between forward and
reverse for at least five minutes.
Shut down prime mover, remove gauges, and plug ports.
Check reservoir level and add fluid if necessary.
4.6 HYDRAULIC COMPONENT START-UP
PROCEDURES & RECOMMENDATIONS
From a hydrostatic component standpoint, the goal at
system start up is to put into functional operation, the
hydrostatic system in such a way as to preserve the
designed life span of the system. The following start-up
procedure should be adhered to whenever a new pump
or motor is initially installed into a machine, or a system is
restarted after either a pump or motor has been removed
and/or replaced.
THE FOLLOWING PROCEDURE MAY REQUIRE THE MACHINE TO
BE DISABLED (WHEELS RAISED OFF THE GROUND, WORK
FUNCTIONS DISCONNECTED, ETC.) WHILE PERFORMING THE
PROCEDURE IN ORDER TO PREVENT INJURY. TAKE NECES-
SARY SAFETY PRECAUTIONS BEFORE MOVING THE VEHICLE/
MACHINE.
Prior to installing the pump and/or motor, inspect the
unit(s) for damage that may have been incurred during
shipping and handling. Ensure all system components
(reservoir, hoses, valves, fittings, heat exchanger, etc.) are
clean prior to filling with fluid.
Fill the reservoir with recommended hydraulic fluid. This
fluid should be passed through a 10 micron (nominal, no
bypass) filter prior to entering the reservoir. The use of
contaminated fluid will cause damage to the components,
which may result in unexpected vehicle/machine move-
ment.
NOTE: If a pump or motor is being replaced due to internal
damage, the remaining units (pump or motors) need
to be inspected for damage and contamination, and
the entire hydraulic system will need to be flushed
and the fluid replaced. Failure to do so may cause
considerable damage to the entire system.
The inlet line leading from the reservoir to the pump must
be filled prior to start-up. Check the inlet line for property
tightened fittings and make sure it is free of restrictions
and air leaks.
NOTE: In most cases, the reservoir is above the pump inlet
so that the pressure head created by the higher oil
level helps to keep the inlet pressures within an
acceptable range and prevent high vacuum levels.
However, due to hose routing or low reservoir loca-
tions, there may be air trapped within this line. It is
important to ensure that the air is bled from this line.
This can be accomplished by loosening the hose at
the fitting closest to the pump. When oil begins to
flow, the line is full, the air has been purged, and the
fitting can be retightened to its specified torque. If the
tank needs to be pressurized in order to start the
flow of oil, a vacuum reading should be taken at the