JLG G5-18A Service Manual - Manual (Page 88)

Hydraulic System
8.14 G5-18A/2505
8.10 VALVES AND MANIFOLDS
8.10.1 Main Control Valve
The main control valve is mounted on the rear of the
machine behind the rear access panel.
The main control valve assembly consists of various
working sections with their own valve assemblies, each
providing a specific hydraulic function. The section
assemblies are the inlet/outlet (1), lift/lower (2), tilt (3),
auxiliary (4), extend/retract (5) and end cap (6) sections.
a. Main Control Valve Removal
1. Park the machine on a firm, level surface, 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 an Do Not Operate Tag on both the ignition
key switch and the steering wheel, stating that the
machine should not be operated.
3. Remove the rear panel. Allow the hydraulic fluid to
cool.
4. Thoroughly clean the main control valve and
surrounding area, including all hoses and fittings,
before proceeding.
5. Place a suitable container to catch hydraulic fluid
drainage beneath the frame.
6. Label, disconnect and cap all the hydraulic hoses
attached to the main control valve. Cap all fittings
and openings to keep dirt & debris from entering the
hydraulic system.
7. Wipe up any hydraulic fluid spillage in, on, near and
around the machine and the work area.
8. Remove the four bolts securing the main control
valve to the frame bracket.
b. Main Control Valve Disassembly
1. To disassemble the individual sections of the main
control valve, remove the nuts from the end of the tie
rod. Pull the tie rods out through the sections.
2. Disassemble each section assembly as required.
Some sections include a pre-adjusted relief valve that
regulates pressure in a specific circuit.
Disassemble each Valve Section
1. Carefully separate the inlet/outlet section from the lift/
lower section.
2. Remove the o-rings from between the two sections.
3. Carefully separate each remaining section being
careful not to lose the load sense shuttle ball.
4. Remove both end caps from each end of the valve
sections then remove each control spool.
5. Remove any check valves, compensator valves,
anti-cavitation valves or shock valves from each
individual valve section if equipped.
6. 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
trichlorethylene, 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.
MY2110
2 3 4 5 FRONT OF MACHINE
1
6
NOTICE
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.