JLG 660SJ Service Manual - Manual (Page 134)

SECTION 5 - HYDRAULICS
5-2 – JLG Lift – 3120840
ports. If leakage occurs at a rate of 6-8 drops per
minute or more, the piston seals are defective and
must be replaced.
5. If no repairs are necessary or when repairs have
been made, replace counterbalance valve and care-
fully connect hydraulic hoses to cylinder port block.
6. If used, remove lifting device from upright or remove
prop from below main boom, activate hydraulic sys-
tem and run cylinder through one complete cycle to
check for leaks.
Cylinders With Dual Counterbalance Valves
(Articulating Jib Boom Lift, and Slave), Slave Level, Lower
Lift, Upright level, Main Telescope and Tower Telescope.
OPERATE ALL FUNCTIONS FROM GROUND CONTROL STATION
ONLY.
1. Using all applicable safety precautions, activate
hydraulic system.
IF WORKING ON THE TOWER BOOM LIFT CYLINDER, RAISE
TOWER BOOM HALFWAY, FULLY ELEVATE MAIN BOOM WITH
TELESCOPE CYLINDER FULLY RETRACTED AND ATTACH AN
OVERHEAD CRANE TO THE UPRIGHT FOR SUPPORT, LEAVING
APPROXIMATELY 2.5 CM OF SLACK IN CHAIN OR SLING FOR
TEST PURPOSES. IF WORKING ON THE UPRIGHT LEVEL, RAISE
THE TOWER BOOM HALFWAY, THEN RAISE MAIN BOOM TO HOR-
IZONTAL AND POSITION A SUITABLE BOOM PROP APPROXI-
MATELY 2.5 CM BELOW MAIN BOOM. IF WORKING ON THE
PLATFORM LEVEL CYLINDER, STROKE PLATFORM LEVEL CYL-
INDER FORWARD UNTIL PLATFORM SITS AT A 45 DEGREES
ANGLE.
2. Shut down hydraulic system and allow machine to
sit for 10-15 minutes. If machine is equipped with
bang-bang or proportional control valves, turn IGNI-
TION SWITCH to ON, move control switch or lever
for applicable cylinder in each direction, then turn
IGNITION SWITCH to OFF. If machine is equipped
with hydraulic control valves, move control lever for
applicable cylinder in each direction. This is done to
relieve pressure in the hydraulic lines. Carefully
remove hydraulic hoses from appropriate cylinder
port block.
3. There will be initial weeping of hydraulic fluid, which
can be caught in a suitable container. After the initial
discharge, there should be no 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.
4. To check piston seals, carefully remove the counter-
balance valve from the retract port. After initial dis-
charge, there should be no further leakage 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.
5. If no repairs are necessary or when repairs have
been made, replace counterbalance valve and care-
fully connect hydraulic hoses to cylinder port block.
6. If used, remove lifting device from upright or remove
prop from below main boom, activate hydraulic sys-
tem and run cylinder through one complete cycle to
check for leaks.
5.3 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.
Disassembly
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 CYLINDER TO THE END OF STROKE.
RETRACT CYLINDER SLIGHTLY TO AVOID TRAPPING PRES-
SURE.
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.
3. If applicable, remove the cartridge-type holding
valve and fittings from the cylinder port block. Dis-
card o-rings.