JLG G12-55A AccuPlace Service Manual - Manual (Page 114)

Hydraulic System
8.24 G10-55A & G12-55A AccuPlace
valve, then slowly open the bleed valve. Do not
reduce the pre-charge by depressing the valve core
with a foreign object. High pressure may rupture the
rubber valve seat.
15. When finished pre-charging the accumulator, turn
the handle all the way out on the gas chuck, then
open the bleed valve.
16. Remove the fill kit assembly from the gas valve on
the accumulator. Check for precharge leak using a
common leak reactant.
17. Replace the gas valve cap and valve guard. Torque
to 10-15 in-lbs (11.5-17 cm kg).
8.10 HYDRAULIC CYLINDERS
8.10.1 General Cylinder Removal
Instructions
1. Remove any attachment from the machine. Park the
machine on a firm level surface and fully retract the
boom. Allow sufficient work space around the
hydraulic cylinder being removed. Support the boom
if the lift/lower cylinder is being removed. Place the
travel select lever in (N) NEUTRAL, engage the park
brake, shut the engine OFF and chock wheels.
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 engine cover. Allow the system fluids to
cool.
4. Label, disconnect and cap or plug hydraulic hoses in
relation to the cylinder.
Note: Prior to removing the extend/retract cylinder,
remove the telescope valve assembly attached to the
cylinder to prevent damage to the valve. Refer to Section
8.8.5, “Telescope Valve.”
5. Attach a suitable sling to an appropriate lifting device
and to the cylinder. Ensure the device used can
actually support the cylinder.
6. Remove the lock bolt and/or any retaining clips
securing the cylinder pins. Remove the cylinder pins.
7. Remove the cylinder.
8. Wipe up any hydraulic fluid spillage in, on, near and
around the machine, work area and tools.
a. General Cylinder Disassembly
1. Clean the cylinder with a suitable cleaner before
disassembly. Remove all dirt, debris and grease
from the cylinder.
2. Clamp the barrel end of the cylinder in a soft-jawed
vise or other acceptable holding equipment if
possible.
Note: Avoid using excessive force when clamping the
cylinder in a vise. Apply only enough force to hold the
cylinder securely. Excessive force can damage the
cylinder tube.
3. If applicable, remove the counterbalance valve from
the side of the cylinder barrel.
Note: DO NOT tamper with or attempt to adjust the
counterbalance valve cartridge. If adjustment or
replacement is necessary, replace the counterbalance
valve with a new part.
4. Extend the rod as required to allow access to the
base of the cylinder.
Note: Protect the finish of 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 from the tube. A considerable amount of force
will be needed to remove the head gland. Carefully
WARNING
Significant pressure 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 could penetrate the skin.
MZ0400