JLG 4017 Service Manual - Manual (Page 104)

Hydraulic System
8.4 4017
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.
4. 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.
5. 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. Checking Function Pressures
All hydraulic system function pressures can be checked
at one location. 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 345 bar
(5000 psi) gauge to the test port located at the top
right corner of the main control valve (1).
Note: See Section 8.7.1, “Main Control Valve,” for
complete valve breakdown.
3. Start the machine, run the engine at full throttle and
bottom the boom in function.
Note: It is possible to see maximum system pressure by
activating and bottoming any of the hydraulic functions.
4. With the engine running at full throttle and the
hydraulic function bottomed, the gauge should read
250 bar (3625 psi) +/- 5 bar (70 psi).
WARNING:
Hydraulic oil leaking under
pressure can penetrate the skin and cause
severe personal injury. DO NOT use your hand
or any part of your body to check for hydraulic
leaks. When checking for hydraulic leaks, wear
safety glasses and gloves to help provide
protection from spraying hydraulic oil. Use a
piece of cardboard or paper to search for
leaks.
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