JLG 534D-10 - Manual (Page 140)

Hydraulic System
8.16 534D-9, 534D-10 & 544D
8.8 CONTROL VALVES
8.8.1 Main Control Valve
The main control valve is mounted on the frame of the
cab below the seat.
The main control valve assembly consists of five working
sections with their own valve assemblies, each providing
a specific hydraulic function.
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, stating that the
machine should not be operated.
3. Open the engine cover and the hydraulic oil
reservoir/fuel tank cover. Allow the system fluids to
cool.
4. Disconnect the battery negative (-) cable from the
battery negative (-) terminal.
5. With the engine OFF, relieve any trapped pressure in
the hydraulic system.
6. Thoroughly clean the main control valve and
surrounding area, including all hoses and fittings,
before proceeding.
7. Place a suitable container to catch hydraulic fluid
drainage beneath the frame.
8. Label, disconnect and cap all the hydraulic hoses,
tubes and wires at the main control valve.
9. Wipe up any hydraulic fluid spillage in, on, near and
around the machine and the work area.
10. Remove the three bolts, washer and nuts (3)
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 (4). Pull the tie rods out through the sections.
2. Disassemble each section assembly as required.
Note: Some sections include a pre-adjusted relief valve
that regulates pressure in a specific circuit.
Disassemble each Valve Section
1. Carefully separate the outlet section from the auxiliary
section.
2. Remove the o-rings from between the two sections.
3. Carefully separate each remaining sections.
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.
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 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.
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.