JLG sky trak mmv Service Manual page 397

b. Unloader Valve Disassembly, Inspection and
Assembly
1. Safely secure the unloader valve (10) in a bench vise
or by other suitable means.
WARNING:
be trapped inside the valve. Exercise caution
when removing a valve. Escaping hydraulic fluid
under pressure can penetrate the skin, causing
death or serious injury.
2. Remove the o-ring boss plug (11).
3. Remove the relief valve (12).
4. Remove the differential pressure sense valve (13).
5. Remove the diagnostic test nipples (14) and
remaining fittings (15).
15
11 15
6. Clean metal parts in an approved solvent such as
triclorethylene and blow dry.
7. Inspect all sealing surfaces. They must be clean,
smooth and free of damage, and have no indication
of wear. Replace parts if damaged or worn.
Note: ALWAYS replace seals, o-rings, gaskets, etc.,
with new parts to help ensure proper sealing and opera-
tion. Lubricate seals and o-rings with clean hydraulic oil.
8. Install the o-ring boss plug (11).
9. Install the relief valve assembly (12) and torque to
35-40 lb/ft (47-54 Nm).
10. Install the differential pressure sense valve assembly
(13) and torque to 80-90 lb/ft (108-122 Nm).
11. Install diagnostic nipples (14) and fittings (15).
Model MMV Rev. 12/04
Significant pressure may
12
13
10
15
16
14
c. Unloader Valve Installation
1. Secure the unloader valve (1) to the vehicle frame near
the engine with the three capscrews (7),
lockwashers (8) and washers (9). Torque the
capscrews to 31 lb/ft (42 Nm).
Note: ALWAYS replace seals, o-rings, gaskets, etc.,
with new parts to help ensure proper sealing and opera-
tion. Lubricate seals and o-rings with clean hydraulic oil.
2. Connect the hydraulic lines to their appropriate ports
on the unloader valve.
3. Check the routing of all hoses, wiring and tubing for
sharp bends or interference with any rotating
members. All tube and hose clamps must be tight.
WARNING:
operation in closed areas with inadequate ven-
tilation. Failure to properly ventilate exhaust
fumes can result in death or serious injury.
4. Start the engine and run at approximately one-third
to one-half throttle for approximately one minute
without moving the vehicle or operating any
hydraulic functions.
WARNING:
under pressure can penetrate the skin and
cause severe personal injury. DO NOT use
your hand or any part of your body to check for
hydraulic leaks. When checking for hydraulic
leaks, wear safety glasses and gloves to help
provide protection from spraying hydraulic oil.
Use a piece of cardboard or paper to search
for leaks.
MM4640
5. Inspect for leaks and check all fluid levels. The
hydraulic reservoir oil level must be to the middle of
the sight gauge.
Note: Check for leaks and tighten fittings or repair as
required before continuing. Wipe up any hydraulic fluid spill-
age in, on, near and around the vehicle, work area and tools.
d. Unloader Valve Pressure Check Test
1. Monitor the valve pressure at the VG test port (16) on
the unloader valve. It should be at 200 ±50 psi
(13,8 ±3,4 bar) within moments after starting the engine.
Adjust the differential pressure sense valve as required.
2. Check the pressure at the VG test port (16) on the
unloader valve while performing the boom lower
function. It should be 3500 ±100 psi (241 ±6,9 bar).
Adjust the relief valve as required.
Hydraulic System
Avoid prolonged engine
Hydraulic oil leaking
9.99