JLG 150HAX Service Manual - Manual (Page 98)

SECTION 5 - HYDRAULICS
5-2 – JLG Lift – 3120817
5.3 CYLINDER CHECKING PROCEDURES
NOTE: Cylinder checks must be performed any time a cylin-
der component is replaced or when improper system
operation is suspected.
Cylinders w/o Counterbalance Valves -
Front and Rear Steer Cylinders, Front and
Rear Frame Lift Cylinders, Upper Master
Cylinder, Lower Master Cylinder, Front and
Rear Axle Extension Cylinders
OPERATE FUNCTIONS FROM GROUND CONTROL STATION ONLY.
1. Using all applicable safety precautions, activate
engine and fully extend cylinder to be checked. Shut
down engine.
2. Carefully disconnect hydraulic hose from retract port
of cylinder. 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 retract port.
3. Activate engine and activate cylinder extend func-
tion. Check retract port for leakage.
4. If cylinder leakage is 6-8 drops per minute or more,
piston seals are defective and must be replaced. If
cylinder retract port leakage is less than 6-8 drops
per minute, carefully reconnect hose to retract port
and retract cylinder.
5. With cylinder fully retracted, shut down engine and
carefully disconnect hydraulic hose from cylinder
extend port.
6. Activate engine and activate cylinder retract func-
tion. Check extend port for leakage.
7. If cylinder leakage is 6-8 drops per minute or more,
piston seals are defective and must be replaced. If
extend port leakage is less than 6-8 drops per
minute, carefully reconnect hose to extend port,
then activate cylinder through one complete cycle
and check for leaks.
Cylinders w/Single Counterbalance Valves
- Main Lift Cylinder, Tower Telescope
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
TOWER BOOM AND THEN RAISE THE MAIN BOOM TO HORIZON-
TAL. SUPPORT THE MAIN BOOM USING A SUITABLE BOOM PROP
OR OVERHEAD LIFTING DEVICE.
2. If working on the main lift cylinder, raise the tower
boom and then raise the main boom to horizontal.
Place a suitable boom prop approximately 1 in. (2.5
cm) below the boom. If working on the tower tele-
scope cylinder, raise the tower boom above horizon-
tal and extend the fly section 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.