Decompression Valve - JLG G5-18A Service Manual

Hydraulic System
8.10.10

Decompression Valve

The decompression valve is located on the frame at the
left rear corner above the main control valve.
Verify the correct operation of the decompression valve
solenoid before considering replacement of the valve.
The housing of the decompression valve is not
serviceable and must be replaced if defective.
a. Decompression Valve Removal
1. Park the machine on a firm, level surface, fully
retract the boom, raise 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. Open the engine covers. Allow the system fluids to
cool.
4. Label or otherwise mark the hydraulic hoses in
relation to the decompression valve. Disconnect and
cap all hoses, fittings, solenoid wire terminal leads,
etc.
5. Remove the capscrews that attach the valve to the
frame.
6. Remove the decompression valve from the machine.
Wipe up any hydraulic fluid spillage in, on, near and
around the machine.
b. Decompression Valve Disassembly, Cleaning,
Inspection and Assembly
1. Place the decompression valve assembly on a
suitable work surface.
2. Remove the solenoid valve and cartridge from the
decompression valve housing.
3. Clean all components with a suitable cleaner before
inspection.
4. Inspect the solenoid cartridge for proper operation.
Check by shifting the spool to ensure that it is
functioning properly. Check that the spring is intact.
Inspect the cartridge interior for contamination.
5. Inspect internal passageways of the decompression
valve for wear, damage, etc. If inner surfaces of the
manifold DO NOT display an ultra-smooth, polished
finish, or components are damaged in any way,
replace the manifold or appropriate part. Often, dirty
hydraulic fluid causes failure of internal seals and
damage to the polished surfaces within the unit
8-22
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.
6. Install the solenoid valve and cartridge in the
decompression valve housing.
c. Decompression Installation
1. Attach the decompression valve to the mounting
plate on the frame using the socket head capscrews.
2. Connect the hydraulic hoses, fittings, solenoid wire
terminal leads, etc., to the inching valve.
3. Check the routing of all hoses, wiring and tubing for
sharp bends or interference with any rotating
members, and install tie wraps and/or protective
conduit as required. Tighten all tube and hose clamps.
4. Start the engine and run at approximately 1/3-1/2
throttle for about one minute, without moving the
machine or operating any hydraulic functions.
5. Inspect for leaks and check the level of the hydraulic
fluid in the reservoir. Shut the engine OFF.
Note: Check for leaks and repair as required before
continuing. Add hydraulic fluid to the reservoir as needed.
6. Wipe up any hydraulic fluid spillage in, on, near and
around the machine, work area and tools.
7. Close and secure the engine covers.
d. Decompression Valve Test
1. Conduct a dump pressure check of the hydraulic
circuit. Refer to Section 9.4.1, "Before S/N
TBS00627," or Section 8.6, "Hydraulic Schematics."
2. Check decompression valve for proper function.
MY287
G5-18A, 2505