JLG 740AJ, Service And Maintenance Manual

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SECTION 5 - BASIC HYDRAULIC INFOR M ATION AND SCHE M ATICS
5-6 3121160
Cylinders With Dual Counterbalance Valves
Articulating Jib Boom Lift, Slave Level, Tower Lift, Upright level
and Main Telescope.
OPERATE ALL FUNCTIONS FROM GROUND CONTROL STATION ONLY.
1. Using all applicable safety precautions, activate hydrau-
lic system.
IF WORKING ON THE TOWER BOOM LIFT C YLINDER, RAISE TOWER BOOM
HALFWAY, FULLY ELEVATE MAIN BOOM WITH TELESCOPE CYLINDER FULLY
RETRACTED AND ATTACH AN OVERHEAD CRANE TO THE UPRIGHT FOR SUP-
PORT, 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 SUP-
PORT WITH A CRANE OR SUITABLE LIFTING DEVICE, APPROXIMATELY 1 INCH
(2.54 CM) BELOW MAIN BOOM. IF WORKING ON THE PLATFORM LEVEL CYLIN-
DER, 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 IGNITION 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 direc-
tion. 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 min-
ute or more, the counterbalance valve is defective and
must be replaced.
4. To check piston seals, carefully remove the counterbal-
ance 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,
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 carefully con-
nect 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.