JLG 600SC_660SJC Service Manual - Manual (Page 88)

SECTION 5 - HYDRAULICS
5-2 – JLG Lift – 3120898
6-8 drops per minute or more, cylinder repairs must
be made.
Cylinders With Single Counterbalance Valve
Upper Lift Cylinder.
IMPORTANT
OPERATE ALL FUNCTIONS FROM GROUND CONTROL STATION
ONLY.
1. Using all applicable safety precautions, activate
hydraulic system.
WHEN WORKING ON THE MAIN LIFT CYLINDER, RAISE THE
BOOM TO HORIZONTAL AND PLACE A BOOM PROP APPROXI-
MATELY 1 INCH (2.54 CM) BELOW THE MAIN BOOM. DO NOT
WORK ON THE CYLINDER WITHOUT A SUITABLE PROP IN
PLACE.
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.
Cylinders With Dual Counterbalance Valves
(Articulating Jib Boom Lift, and Slave), Slave Level, Lower
Lift, Upright level, Main Telescope and Tower Telescope.
IMPORTANT
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 1 INCH (2.54 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 HORIZONTAL AND POSITION A SUITABLE BOOM
PROP APPROXIMATELY 1 INCH (2.54 CM) BELOW MAIN BOOM. IF
WORKING ON THE PLATFORM LEVEL CYLINDER, STROKE PLAT-
FORM LEVEL CYLINDER 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.