JLG G12-55A Service Manual - Manual (Page 132)

Hydraulic System
8-16 G10-55A, G12-55A
12. Remove the four bolts, washers and nuts (1)
securing the main control valve to the frame.
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). 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.
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 from the
lift/lower section.
2. Remove the o-rings from between the two sections.
3. Carefully separate each remaining sections, 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 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
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.
8.7.2 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 control spool being careful not to nick or
scratch the valve section bore or the control spool.
3. Install the end caps on each end of the valve
section.
Assemble the Main Control Valve.
1. Place all three tie rods (2) with the washers and nuts
through 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 tilt control valve section over the three tie
rods and slide onto the end main control valve
section.
MAL0730
1
1
1
1
MY1200
2