JLG 4017PS Service Manual - Manual (Page 135)

8-3 3706PS, 3707PS, 4014PS, 4017PS, 33.7, 37.6, 37.7
Hydraulic System
8.2 SAFETY INFORMATION
Petroleum-based hydraulic fluids are used in this
machine. The temperature of hydraulic fluid increases
during the operation of various hydraulic functions. A
heated petroleum-based hydraulic fluid presents a fire
hazard, especially when an ignition source is present.
Accordingly, periodically inspect all hydraulic system
components, hoses, tubes, lines, fittings, etc. Carefully
examine any deterioration and determine whether any
further use of the component would constitute a hazard.
If in doubt, replace the component.
Whenever you disconnect a hydraulic line, coupler, fitting
or other component, slowly and cautiously loosen the part
involved. A hissing sound or slow seepage of hydraulic
fluid may occur in most cases. After the hissing sound
has ceased, continue removing the part. Any escaping oil
should be directed into an appropriate container. Cap or
otherwise block off the part to prevent further fluid
seepage.
Hydraulic system maintenance will, at times, require that
the engine be operated. Always follow safety precautions.
A major cause of hydraulic component failure is
contamination. Keeping the hydraulic fluid as clean as
possible will help avoid downtime and repairs. Sand, grit
and other contaminants can damage the finely machined
surfaces within hydraulic components. If operating in an
exceptionally dirty environment, change filters and
inspect the fluid more often. When servicing the system,
cap or plug hydraulic fittings, hoses and tube assemblies.
Plug all cylinder ports, valves and the hydraulic reservoir,
and pump openings until installation occurs. Protect
threads from contamination and damage.
Some hydraulic functions are actuated by interfacing with
electrical system components (switches, solenoids and
sensors). When the hydraulic system is not functioning
properly, check the electrical aspect of the malfunctioning
circuit also.
Some hydraulic functions are actuated by interfacing with
electrical system components (switches, solenoids and
sensors). When the hydraulic system is not functioning
properly, check the electrical aspect of the malfunctioning
circuit also. Refer to Section 9.8, “Electrical System
Schematics,” in this manual.
8.3 SPECIFICATIONS
Refer to Section 2.4, “Specifications,” for hydraulic
system specifications.
8.4 HYDRAULIC PRESSURE DIAGNOSIS
8.4.1 Pressure Checks and Adjustments
When diagnosing trouble in the hydraulic system, use the
hydraulic testing information in Section 8.5.1, “Hydraulic
Pressures.”
In general, follow the steps below whenever conducting
pressure checks and performing adjustments:
1. Park the machine on a firm, level surface. Engage
the park brake, place the travel select lever in (N)
NEUTRAL, level the boom and turn the engine OFF.
2. At the proper test port, install a pressure gauge
capable of measuring at least 10% more pressure
than that which the circuit being checked operates
under.
3. Start the engine. Operate machine functions several
times to allow hydraulic oil to reach operating
temperature. The hydraulic oil temperature should
be between 38-49° C (100-120° F). If a temperature
gauge or thermometer is unavailable, the hydraulic
oil reservoir should be warm to the touch.
4. Refer to Section 8.5.1, “Hydraulic Pressures,” for
testing procedures.
5. Fully depress the accelerator pedal if required. Place
and hold the joystick in the position needed to
operate the particular machine function being
checked. Continue holding the joystick in position
until pressure readings are taken.
6. Check the pressure gauge reading. It should read as
specified in the Pressure Readings column of the
charts found in Section 8.5.1, “Hydraulic Pressures.”
If the reading is not as specified, turn the engine
OFF and check other components in the system.
Verify that all related hydraulic components and
electrical switches, sensors, solenoids, etc. are
operating correctly.
7. Adjust the relief valve (1) by turning the adjustment
screw. Turning clockwise will increase the pressure;
turning the screw counterclockwise will decrease the
pressure.
8. Start the engine and check the pressure again. Turn
the engine OFF. If there is pressure reading in the
gauge, bleed it off then disconnect or remove the
pressure gauge from the machine.
WARNING
DO NOT service the machine without following all
safety precautions as outlined in Section 1, “Safety
Practices,” of this manual.