JLG sky trak mmv Service Manual page 405

Disassemble the Relief Valve
(Extend/Retract and Lift/Lower Sections)
On the extend/retract section (1), one relief valve (2) is on
the "B" side (3) and is preset at 3750 ±50 psi (258 ±3,5
bar); the other relief valve (2) is on the "A" side (4) and is
preset at 3000 ±50 psi (207 ±3,5 bar). On the lift/lower
section (5), the relief valve (2) is on the "A" side (6) and is
preset at 3000 ±50 psi (207 ±3,5 bar).
Note: The internal parts of the relief valves can be dis-
assembled without removing the relief valve body from
the valve section. Skip to step 2 to start disassembly of
the relief valve.
1. Remove the relief valve (2) and o-ring (7) from the
appropriate section.
2. Grip the relief valve body (8) with a suitable tool and
use another tool to remove the nut (9), revealing an
adjustment screw (10) and an o-ring (11).
3. Remove the spring (12) and poppet (13) from the
plug (14).
4. Remove the o-ring (15), large spring (16), back-up
ring (17), o-ring (18), small spring (19), poppet (20),
o-ring (21), back-up ring (22), small poppet (23) and
large poppet (24) from the body (8).
Disassemble the Lift/Lower Section
1. Carefully separate the lift/lower section (5) from the
mid-inlet section (25). Avoid dislodging or losing the
shuttle (26) between the lift/lower (5) and mid-inlet
(25) sections.
2. Remove the o-ring (27) from between the two
sections. Remove the shuttle (28), spring (29) and
poppet (30) from the lift/lower section (5).
3. Remove the anti-void assembly (31) and o-ring (32)
from the lift/lower section (5).
4. Remove the relief valve (2) following the Relief Valve
(Extend/Retract and Lift/Lower Sections) procedure.
5. Remove both socket head capscrews (33) securing
the end mechanism (34) to the lift/lower section (5).
6. Remove the retainer (35), spool cap (36) and
o-ring (37) from the end mechanism (34).
7. Remove both socket head capscrews (38) securing
the other end mechanism (39) to the lift/lower
section (5).
Model MMV Rev. 12/04
8. Remove the retainer (40).
9. Remove the spool cap (41) by unthreading it from
the spool cap retainer (48).
10. Hold the spool from turning while removing the spool
end (42).
11. Remove the flat washer (43), spring (44), spacer
(45), another flat washer (46), o-ring (47), spool cap
retainer (48) and o-ring (49) from this end mechanism
(39).
Disassemble the Mid-Inlet Section
1. Remove the shuttle (26) from the mid-inlet
section (25).
2. Remove the shut-off plug (50) and o-ring (51).
3. Remove the plug (52) and o-ring (53).
d. Main Control Valve Parts Cleaning
Clean all components with a suitable cleaner, such as tri-
clorethylene, before continuing. Blow dry.
e. 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 hy-
draulic fluid causes failure of internal seals, damage to
the polished surfaces within the component, and wear of
and/or harm to other parts.
Carefully remove the spools from each section and in-
spect for contamination, scratches, scoring or discolora-
tion. If any damage is noted the sections with spools must
be replaced as a complete assembly. The spools are not
serviced separately.
Hydraulic System
9.107