JLG 150HAX Service Manual - Manual (Page 99)

SECTION 5 - HYDRAULICS
3120817 – JLG Lift – 5-3
Cylinders w/Dual Counterbalance Valve -
Main Telescope Cylinder, Tower Lift
Cylinder, Platform Slave Level Cylinder
OPERATE ALL FUNCTIONS FROM GROUND CONTROL STATION
ONLY.
1. Using all applicable safety precautions, activate
hydraulic system.
2. If working on the main telescope cylinder, raise the
tower boom and then raise the main boom above
horizontal. Extend the main fly boom approximately
1 foot (30.5 cm). If working on the platform slave
level cylinder, stroke platform level cylinder forward
until platform sits at a 45 degree angle.
3. Shut down hydraulic system and allow machine to
sit for 10-15 minutes. Turn ignition switch to ON,
move control switch or lever for applicable cylinder
in each direction, then turn ignition switch to OFF.
This is done to relieve pressure in the hydraulic
lines. Carefully remove hydraulic hoses from appro-
priate cylinder port block.
4. There will be initial weeping of hydraulic fluid which
can be caught in a suitable container. After the initial
discharge, there should not be any 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.
5. To check piston seals, carefully remove the counter-
balance valve from the retract port. After initial dis-
charge, there should not be any 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.
6. If no repairs are necessary or when repairs have
been made, replace counterbalance valve and care-
fully reconnect hydraulic hoses to cylinder port
block.
7. Activate hydraulic system and run cylinder through
one complete cycle to check for leaks.
5.4 CYLINDER REMOVAL AND
INSTALLATION
Tower Telescope Cylinder Removal
NOTE: The tower boom can be telescoped without elevating
the tower by overriding the plunger valves. Refer to
Figure 4-1., Boom Mounted Limit Switches and
Valves Installation.
MAKE SURE THE TOWER BOOM IS NOT EXTENDED BEYOND
WHAT IS NEEDED TO GAIN ACCESS TO THE ATTACH PINS.
MAKE SURE THE TOOLS USED TO OVERRIDE THE PLUNGER
VALVE IS REMOVED BEFORE RETURNING THE MACHINE TO SER-
VICE.
1. Place machine on a flat and level surface, with boom
in the horizontal position and extended just enough
so that the fly section cylinder attach pins are
exposed.
2. Shut down engine. Support main boom and tower
boom with props or overhead lifting devices.
3. Remove four bolts and lockwashers securing tele-
scope cylinder attach plate to base end of tower
boom.
4. Remove four bolts and lockwashers securing tele-
scope cylinder attach plate to port block of tele-
scope cylinder. Remove attach plate.
HYDRAULIC LINES AND PORTS SHOULD BE CAPPED IMMEDI-
ATELY AFTER DISCONNECTING LINES TO AVOID THE ENTRY OF
CONTAMINANTS INTO THE SYSTEM.
5. Tag and disconnect hydraulic lines to telescope cyl-
inder. Use suitable containers to retain any residual
hydraulic fluid. Cap hydraulic lines and ports.