JLG 800A_AJ ANSI Service Manual - Manual (Page 286)

SECTION 5 - HYDRAULICS
5-6 – JLG Lift – 3120740
Cylinders With Dual Counterbalance Valves
(Articulating Jib Boom Lift, and Slave, Slave Level, Tower
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 UPPER 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 UPPER
BOOM TO HORIZONTAL, AND SUPPORT WITH A CRANE OR SUIT-
ABLE LIFTING DEVICE, APPROXIMATELY 1 INCH (2.54 CM)
BELOW UPPER BOOM. IF WORKING ON THE PLATFORM LEVEL
CYLINDER, STROKE PLATFORM 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 upper boom, activate hydraulic
system and run cylinder through one complete cycle
to check for leaks.