JLG 4017PS Service Manual - Manual (Page 147)

8-15 3706PS, 3707PS, 4014PS, 4017PS, 33.7, 37.6, 37.7
Hydraulic System
a. Main Control Valve Removal
1. Park the machine on a firm, level surface, level the
machine, fully retract the boom, lower the boom,
place the transmission control lever in
(N) NEUTRAL, engage the park brake and shut the
engine OFF.
2. Place a Do Not Operate Tag on both the ignition key
switch and the steering wheel.
3. Open the engine cover. Allow the system fluids to
cool.
4. Properly disconnect the battery.
5. Thoroughly clean the main control valve and
surrounding area, including all hoses and fittings,
before proceeding.
6. Place a suitable container to catch hydraulic fluid
drainage beneath the frame.
7. Drain the hydraulic oil reservoir. Refer to Section
8.7.1, “Hydraulic Oil Reservoir Draining.”
8. Label, disconnect and cap all the hydraulic hoses,
tubes and wires at the main control valve. Slowly
turn hose fittings to allow any trapped pressure in
the hydraulic system to escape.
9. Wipe up any hydraulic fluid spillage in, on, near and
around the machine and the work area.
10. Support the valve and remove the four bolts
securing the main control valve to the frame.
Remove the main control valve.
b. Main Control Valve Disassembly
1. To disassemble the individual sections of the main
control valve, remove the nuts from one end of the
tie rods.
2. Disassemble each section assembly as required.
Some sections include a pre-adjusted relief valve that
regulates pressure in a specific circuit.
Note: DO NOT adjust any of the relief valve assemblies.
Tampering with a relief valve will irrevocably alter
pressure in the affected circuit, requiring recalibration or a
new relief valve.
Disassemble each Valve Section
1. Carefully separate the load sense outlet section (5) from
the next section.
2. Remove the o-rings from between the two sections.
3. Carefully separate each remaining section.
4. Remove any check valves, compensator valves,
anti-cavitation valves or shock valves from individual
valve section if equipped.
5. Keep all parts being removed from individual valve
sections tagged and kept together.
c. Main Control Valve Parts Cleaning
Clean all components with a suitable cleaner, such as
triclorethylene, before continuing. Blow dry.
d. Main Control Valve Parts Inspection
Inspect all parts and internal passageways for wear,
damage, etc. If inner surfaces of any component DO NOT
display an ultra-smooth, polished finish, or are damaged
in any way, replace the damaged part. Often, dirty
hydraulic fluid causes failure of internal seals, damage to
the polished surfaces within the component, and wear of
and/or harm to other parts.
e. Main Control Valve Assembly
Note: ALWAYS replace seals, o-rings, gaskets, etc.,
with new parts to help ensure proper sealing and
operation. Lubricate seals and o-rings with clean
hydraulic oil.
Assemble each Valve Section
1. Reassemble any check valves, compensator valves,
anti-cavitation valves or shock valves from each
individual valve sections if equipped.
2. Install the end caps on each end of the valve
section.
Assemble the Main Control Valve.
1. If removed, install all four tie rods into the end main
control valve section.
2. Stand the end main control valve section on end.
3. Install the proper o-rings and load sense shuttle on
the inner face of the end main control valve section.
Align the next valve section over the three tie rods
and slide onto the end main control valve section.
4. Using the proper o-rings and load sense shuttle,
repeat step three for the remaining valve sections
and lastly the inlet end valve section.