JLG 600SC_660SJC Service Manual - Manual (Page 264)

SECTION 8 - HYDRAULICS
8-4 – JLG Lift – 3121157
7. If extend port leakage is less than 6-8 drops per
minute, carefully reconnect hose to extend port,
than activate cylinder through one complete cycle
and check for leaks. If leakage continues at a rate of
6-8 drops per minute or more, cylinder repairs must
be made.
Cylinders With Single Counterbalance
Valve
Lift Cylinder
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,
Telescope
OPERATE ALL FUNCTIONS FROM GROUND CONTROLS ONLY.
1. Using all applicable safety precautions, activate
hydraulic system.
IF WORKING ON THE PLATFORM LEVEL CYLINDER, STROKE
PLATFORM LEVEL CYLINDER FORWARD UNTIL PLATFORM SITS
AT A 45 DEGREE 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. Remove
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.