JLG 4017RS Service Manual - Manual (Page 134)

Hydraulic System
8-4 3614RS, 4017RS
8.5 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. If oil is cold,
oil level should be visible in the lower gauge window
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.
8.5.1 Hydraulic Pressures
a. Checking Pressure
1. Start the machine and warm the hydraulic system to
operating temperature.
2. Shut off the machine and install a digital or a 345 bar
(5000 psi) gauge to the appropriate test port on the
main control valve.
3. Start the machine, run the engine at idle and bottom
the appropriate hydraulic function. Refer to Section
8.5.1, d. “Pressure Specifications,” for the correct
pressure rating.
b. Adjusting Maximum Hydraulic Pressure
1. Shut the machine off. Remove the cap on the relief (if
necessary).
2. Start the machine and loosen the jam nut on the relief
(1). Turn the relief clockwise to increase pressure or
counter-clockwise to decrease pressure. Set to the
correct pressure.
3. Tighten the jam nut and recheck the pressure at full
throttle. 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 and/or the electrical
schematic to help troubleshoot and correct the
problem.
c. Adjusting Maximum Steering Pressure
1. Shut the machine off.
2. Install a digital or a 345 bar (5000 psi) gauge to the
appropriate test port on the hydraulic manifold.
3. Select 2 wheel steer, run engine at high idle, turn
steering wheel one direction to lock. Hold and check
pressure.
Note: Do Not operate any other function while checking
steering pressure.
Note: The steering pressure is pre-set from the manufacturer
and cannot be adjusted.
4. If the proper pressure cannot be set, use the
accompanying hydraulic schematic and/or the electrical
schematic to help troubleshoot and correct the
problem.