JLG sky trak mmv Service Manual page 450

Hydraulic System
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b. Extend/Retract Cylinder Disassembly
Note: An additional o-ring may be included at the base
of the cylinder rod. This additional o-ring may be dis-
carded, as it served only in a temporarily protective role.
1. Clean the extend/retract cylinder (1) with a suitable
cleaner. Remove all dirt, debris and grease from the
cylinder.
IMPORTANT: Avoid using excess force when clamping
the cylinder in a vise. Apply only enough force to hold the
cylinder securely. Excessive force can damage the cylin-
der tube (2).
2. Secure the extend/retract cylinder in a soft-jawed
vise or other acceptable holding equipment if possible.
WARNING:
may be trapped inside the cylinder. Exercise
caution when removing a counterbalance valve
or a pilot-operated check valve from a cylinder.
Escaping hydraulic fluid under pressure can
penetrate the skin, causing death or serious
injury.
3. Slowly remove the counterbalance valve (3) and the
pilot-operated check valve (4).
9.152
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Significant pressure
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2
IMPORTANT: DO NOT tamper with or attempt to reset
the counterbalance valve cartridge. If adjustment or
replacement is necessary, replace a counterbalance
valve with a new part.
4. Extend the rod (5) as required to allow access to the
base of the cylinder.
IMPORTANT: Protect the finish on the rod at all times.
Damage to the surface of the rod can cause seal failure.
5. Using a pin spanner wrench, unscrew the head
gland (6) from the tube (2). The head gland was
originally torqued to 300-400 lb/ft (407-542 Nm), so
a considerable amount of force is required. Carefully
slide the head gland down along the rod toward the
trunnion end, away from the cylinder tube (2).
IMPORTANT: When sliding the rod and piston assembly
in the tube, prevent the threaded end of the tube from
damaging the piston (7). Keep the rod centered within
the tube to help prevent binding.
6. Carefully pull the rod (5) with all attachments straight
out of the tube (2).
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Model MMV Rev. 12/04
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MM4740