JLG 534D-10 - Manual (Page 130)

Hydraulic System
8.6 534D-9, 534D-10 & 544D
8.4 HYDRAULIC CIRCUITS
This section covers the hydraulic circuits and includes
listings for all hydraulic function pressures, where and
how to check those pressures and a hydraulic schematic.
Electrical and hydraulic functions are often related. Verify
that the electrical components of the circuit are
functioning properly whenever troubleshooting the
hydraulic circuit.
Always check the following before beginning to
troubleshoot a circuit that is not functioning correctly.
1. Check the hydraulic oil level in the reservoir. Oil level
should be to the middle of the sight glass with all
cylinders retracted.
2. Check hoses, tubes, fittings and other hydraulic
components for leaks, bends, kinks, interference, etc.
3. Check for air in the hydraulic system. Erratic machine
performance and/or spongy cylinder operation are
signs of air in the hydraulic system.
If air in the hydraulic system is suspected, you will
hear air leakage when hydraulic fittings are loosened
and see air bubbles in the hydraulic fluid.
Loose fittings, faulty o-rings or seals, trapped oil,
leaks, system opened for service, etc., can cause air
in the system. Determine what is causing air to enter
the system and correct it. Bleed air from the system.
8.4.1 Hydraulic Pressures
a. Charge Pressure
To ensure proper park brake operation, charge pressure
needs to be at proper specification. Control pressure is
modified charge pressure. If charge pressure is low,
control pressure may be low and machine speed
reduced. Thus, drive performance is adversely affected
by low charge pressure. A digital pressure gauge is
recommended.
1. Start the machine and warm the hydraulic system to
operating temperature.
2. Shut off the machine and install a digital or a
10,000 psi (689 bar) gauge to the test port located at
the right side in front of the return filter.Make sure
the gauge can be observed from the operator’s cab.
3. Start the machine, leave the park brake applied.
4. With the engine running at low idle, the gauge
should read a minimum of 380 psi (26 bar).
5. With the engine running at high idle, the gauge
should read a maximum of 480 psi (33 bar).
Note: Throughout test operation, charge pressure
should not drop below 380 psi (26 bar) and should move
toward 480 psi (33 bar) as RPM rises, regardless of how
many functions are being operated simultaneously.
b. Adjusting Charge Pressure
1. Shut the machine off. The charge pump relief (1) is
located at the left side of the hydrostatic drive pump.
Remove the plastic tamper proof cap.
2. Loosen the jam nut on the relief and using an allen
wrench; turn the relief clockwise to increase
pressure or counter-clockwise to decrease pressure.
Start the machine and set the pressure to 380 psi
(26 bar) at low idle.
3. Tighten the jam nut and recheck the pressure at low
and high idle. If the reading is within specification,
shut the machine off, install the safety cap and
remove the gauge from the test port.
4. If the proper pressure cannot be set, use the
accompanying hydraulic schematic, electrical
schematic, and/or Section 6.6, “Hydrostatic Drive
Performance Checks,” to help correct the problem.
c. Steering Pressure
1. Start the machine and warm the hydraulic system to
operating temperature.
2. Shut off the machine and install a digital or a
10,000 psi (689 bar) gauge to the test port located at
the left side in front of the return filter.Make sure the
gauge can be observed from the operator’s cab.
3. Start the machine, leave the park brake applied.
4. Turn the steering wheel left or right until the wheel
hits the steering stop.
MX1050
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