JLG 600SC_660SJC Service Manual - Manual (Page 148)

SECTION 5 - HYDRAULICS
5-4 – JLG Lift – 3121607
Cylinders With Single Counterbalance Valve
(Upper Lift Cylinder)
OPERATE ALL FUNCTIONS FROM GROUND CONTROL STATION ONLY.
1. Using all applicable safety precautions, activate hydrau-
lic system.
WHEN WORKING ON MAIN LIFT CYLINDER, RAISE BOOM TO HORIZONTAL AND
PLACE A BOOM PROP APPROXIMATELY 1 INCH (2.54 CM) BELOW THE MAIN
BOOM. DO NOT WORK ON 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 proportional
control valves, turn IGNITION SWITCH to ON, move con-
trol switch or lever for applicable cylinder in each direc-
tion, 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 hydraulic line pressure. 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 initial dis-
charge, there should be no further leakage from the
ports. If leakage continues at a rate of 6-8 drops per min-
ute or more, counterbalance valve is defective and must
be replaced.
4. To check piston seals, carefully remove counterbalance
valve from the retract port. After initial discharge, there
should be no further leakage from the ports. If leakage
occurs at a rate of 6-8 drops per minute or more, piston
seals are defective and must be replaced.
5. If no repairs are necessary or when repairs have been
made, replace counterbalance valve and connect
hydraulic hoses to cylinder port block.
6. If used, remove lifting device from upright or remove
prop from below main boom. Activate hydraulic system
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 hydrau-
lic system.
IF WORKING ON TOWER BOOM LIFT CYLINDER, RAISE TOWER BOOM HALF-
WAY, FULLY ELEVATE MAIN BOOM WITH TELESCOPE C YLINDER FULLY
RETRACTED. 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 TOWER BOOM
HALFWAY, THEN RAISE MAIN BOOM TO HORIZONTAL AND POSITION A SUIT-
ABLE BOOM PROP APPROXIMATELY 1 INCH (2.54 CM) BELOW MAIN BOOM. IF
WORKING ON PLATFORM LEVEL CYLINDER, STROKE PLATFORM LEVEL CYLIN-
DER 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 proportional
control valves, turn IGNITION SWITCH to ON, move con-
trol switch or lever for applicable cylinder in each direc-
tion, 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 hydraulic line pressure.
3. Carefully remove hydraulic hoses from appropriate cyl-
inder port block. Catch initial weeping of hydraulic fluid
in a suitable container. After 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,
counterbalance valve is defective and must be replaced.
4. To check piston seals, carefully remove counterbalance
valve from retract port. After initial discharge, there
should be no further leakage from the ports. If leakage
occurs at a rate of 6-8 drops per minute or more, piston
seals are defective and must be replaced.
5. If no repairs are necessary or when repairs have been
made, replace counterbalance valve and carefully con-
nect hydraulic hoses to cylinder port block.
6. Remove lifting device from upright or remove prop from
below main boom. Activate hydraulic system and run
cylinder through one complete cycle to check for leaks.