JLG G5-18A Service Manual - Manual (Page 111)

8-21 G5-18A, 2505H, 25.5
Hydraulic System
8.11.8 Priority Valve
.The priority valve is attached at the engine pod frame
directly beside the engine.
Verify the correct operation of the priority valve before
considering replacement of the valve. The priority valve
must be replaced if defective.
a. Priority 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 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 battery and engine covers. Allow the
system fluids to cool.
4. Properly disconnect the battery.
5. Label or otherwise mark the hydraulic hoses in
relation to the priority valve. Disconnect and cap all
hoses, fittings, etc.
6. Remove the capscrews that attach the valve to the
frame.
7. Remove the priority valve from the machine. Wipe up
any hydraulic fluid spillage in, on, near and around
the machine.
b. Priority Valve Disassembly, Cleaning, Inspection
and Assembly
1. Place the priority valve assembly on a suitable work
surface.
2. Label and remove the fittings (3) from the priority
valve housing.
3. Clean all components with a suitable cleaner before
inspection.
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.
4. Install the previously labeled fittings in the priority valve
housing.
c. Priority Valve Installation
1. Attach the priority valve to the mounting plate on the
frame using the socket head capscrews.
2. Connect the hydraulic hoses, fittings, etc., to the
priority valve.
3. Check the routing of all hoses for sharp bends or
interference with any rotating members, and install
tie wraps and/or protective conduit as required.
Tighten all hose clamps.
4. Properly connect the battery.
5. 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.
6. 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.
7. Wipe up any hydraulic fluid spillage in, on, near and
around the machine, work area and tools.
8. Close and secure the battery and engine covers.
9. Remove the Do Not Operate Tags from both the
ignition key and the steering wheel.
d. Priority Valve Test
1. Start the machine and slowly depress the throttle to
1/2 throttle. Turn the steering and engage a boom
function. The steering will continue to respond along
with the engaged boom function.
2. If further troubleshooting is required, refer to Section
8.7, “Hydraulic Schematic.”
MY2971
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