JLG 80HX_HX+6_HXER ANSI Service Manual - Manual (Page 95)

SECTION 5 - HYDRAULICS
3120271 – JLG Lift – 5-3
5.3 CYLINDER CHECKING PROCEDURE
NOTE: Cylinder checks must be performed any time a cylin-
der component is replaced or when improper sys-
tem operation is suspected.
Cylinders Without Counterbalance Valves
(Steer Cylinder and Master Cylinder)
1. Using all applicable safety precautions, activate the
engine and fully extend the cylinder to be checked.
Shut down the engine.
2. Carefully disconnect the hydraulic hose from the
retract port of the cylinder. There will be initial weep-
ing of hydraulic fluid which can be caught in a suit-
able container. After the initial discharge there
should be no further leakage from the retract port.
3. Activate the engine and extend the cylinder.
4. If cylinder retract port leakage is less than 6-8 drops
per minute, carefully reconnect the hose to the port
and retract the cylinder. If leakage continues at a
rate of 6-8 drops per minute or more, cylinder
repairs must be made.
5. With the cylinder fully retracted, shut down the
engine and carefully disconnect the hydraulic hose
from the cylinder extend port.
6. Activate the engine and retract the cylinder. Check
the extend port for leakage.
7. If the extend port leakage is less than 6-8 drops per
minute, carefully reconnect the hose to the extend
port, then activate the cylinder through one com-
plete cycle and check for leaks. If leakage continues
at a rate of 6-8 drops per minute or more, cylinder
repairs must be made.
Cylinders With Single Counterbalance Valve
(Lift Cylinder, Telescope Cylinder and Extend- A-Reach Lift
Cylinder)
OPERATE ALL FUNCTIONS FROM THE GROUND CONTROLS.
1. Using all applicable safety precautions, activate the
hydraulic system.
WHEN WORKING ON THE LIFT CYLINDER, RAISE THE BOOM TO
HORIZONTAL AND PLACE A BOOM PROP APPROXIMATELY 1
INCH (2.50 CM) BELOW THE BOOM. DO NOT WORK ON THE CYL-
INDER WITHOUT A SUITABLE PROP IN PLACE. REFER TO FIG-
URE 5-2.
2. After completing the above, shut down the hydraulic
system and allow the machine to sit for 10-15 min-
utes. Turn the IGNITION SWITCH to ON, move the
control switch or lever for the applicable cylinder in
each direction, then turn the IGNITION SWITCH to
OFF. This is done to relieve pressure in the hydraulic
lines. Carefully remove the hydraulic hoses from the
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 not be any further leakage
from the ports. If leakage continues at a rate of 6-8
drops per minute or more, the following 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.
4. If no repairs are necessary or when repairs have
been made, carefully reconnect the hydraulic hoses
to the appropriate ports.
5. If used, remove the boom prop from beneath the
boom, activate the hydraulic system and run the cyl-
inder through one complete cycle to check for leaks.