JLG 80HX_HX+6_HXER ANSI Service Manual - Manual (Page 96)

SECTION 5 - HYDRAULICS
5-4 – JLG Lift – 3120271
Cylinders With Dual Counterbalance Valves
(Platform Slave Level Cylinder, Lockout Cylinder and
Extend-A-Reach Level Cylinder)
OPERATE ALL FUNCTIONS FROM THE GROUND CONTROL STA-
TION ONLY.
1. Using all applicable safety precautions, activate the
hydraulic system.
2. When working on the platform slave level cylinder,
stroke the platform slave level cylinder forward until
the platform sits at a 45° angle.
3. Shut down the hydraulic system and allow the
machine to sit for 10-15 minutes. If the machine is
equipped with bang-bang or proportional control
valves, turn the IGNITION SWITCH to ON, move the
control switch or lever for the applicable cylinder in
each direction, then turn the IGNITION SWITCH to
OFF. If the machine is equipped with hydraulic con-
trol valves, move the control lever for the applicable
cylinder in each direction. This is done to relieve
pressure in the hydraulic lines. Carefully remove the
hydraulic hoses from the appropriate cylinder port
block.
4. There will be initial weeping of hydraulic fluid which
can be caught in a suitable container. After the initial
discharge, there should not be any further leakage
from the ports. If leakage continues at a rate of 6-8
drops per minute or more, the counterbalance valve
is defective and must be replaced.
5. To check the piston seals, carefully remove the
counterbalance valve from the retract port. After ini-
tial discharge there should not be any further leak-
age from the ports. If leakage occurs at a rate of 6-8
drops per minute or more, the piston seals are
defective and must be replaced.
6. If no repairs are necessary or when repairs have
been made, replace the counterbalance valve and
carefully connect the hydraulic hoses to the cylinder
port block.
7. If used, remove the lifting device from the upright or
remove the prop from below the boom, activate the
hydraulic system and run the cylinder through one
complete cycle to check for leaks.
5.4 CYLINDER REPAIR
NOTE: The following are general procedures that apply to
all of the cylinders on this machine. Procedures that
apply to a specific cylinder will be so noted.
NOTE: See Figure 5-3., Figure 5-4., Figure 5-5., and Figure
5-6. for the breakdown of typical hydraulic cylinders
used on this machine.
Disassembly
IMPORTANT
DISASSEMBLY OF THE CYLINDER SHOULD BE PERFORMED ON
A CLEAN WORK SURFACE IN A DIRT FREE WORK AREA.
1. Connect a suitable auxiliary hydraulic power source
to the cylinder port block fitting.
DO NOT FULLY EXTEND THE CYLINDER TO THE END OF THE
STROKE. RETRACT THE CYLINDER SLIGHTLY TO AVOID TRAP-
PING PRESSURE.
2. Operate the hydraulic power source and extend the
cylinder. Shut down and disconnect the power
source. Adequately support the cylinder rod, if appli-
cable.
ON CYLINDERS WITH DOUBLE HOLDING VALVES, BEFORE
REMOVING HOLDING VALVES, CRACK THE BLEEDERS TO
RELEASE PRESSURE.
3. If applicable, remove the cartridge-type holding
valve and fittings from the cylinder port block. Dis-
card the o-rings.