JLG 120HX ANSI Service Manual - Manual (Page 30)

SECTION 2 - PROCEDURES
2-10 – JLG Lift – 3120686
Cylinders w/Single Counterbalance Valves -
Lift Cylinder, Telescope Cylinder, Extend-A-
Reach Cylinder.
OPERATE ALL FUNCTIONS FROM GROUND CONTROL STATION
ONLY.
1. Using all applicable safety precautions, activate
hydraulic system.
WHEN WORKING ON THE LIFT CYLINDER, RAISE THE BOOM TO
HORIZONTAL AND SUPPORT THE BOOM USING A SUITABLE
BOOM PROP OR OVERHEAD LIFTING DEVICE.
2. If working on the lift cylinder, raise boom to horizon-
tal and place a suitable boom prop approximately 1
inch (2.5 cm) below the boom. If working on the tele-
scope cylinder, raise the boom above horizontal and
extend the fly boom approximately 1 foot (30.5 cm).
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 excess pressure in the
hydraulic lines. Carefully remove hydraulic hoses
from appropriate 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, cylinder repairs must be
made. If the retract port is leaking, the piston seals
are defective and must be replaced. If the extend
port is leaking, the counterbalance valve is defective
and must be replaced.
5. If no repairs are necessary or when repairs have
been made, carefully reconnect hydraulic hoses to
the appropriate ports.
6. If used, remove boom prop or lifting device from
boom, activate hydraulic system and run cylinder
through one complete cycle to check for leaks.
Cylinders w/Dual Counterbalance Valve -
Axle Extension Cylinders, Telescope
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 telescope cylinder, raise the boom
above horizontal and extend the fly boom approxi-
mately 1 foot (30.5 cm). If working on the platform
slave level cylinder, stroke platform level cylinder for-
ward until platform sits at a 45° 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.