JLG 80HX, Service Maintenance Manual

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SECTION 2 - PROCEDURES
2-10 – JLG Lift – 3120863
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 2.5
CM BELOW THE BOOM. DO NOT WORK ON THE CYLINDER WITH-
OUT A SUITABLE PROP IN PLACE. REFER TO FIGURE 2-2.
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.
Cylinders With Dual Counterbalance Valves -
Platform Slave Level Cylinder, Lockout
Cylinder and Extend-A-Reach Level Cylinder
OPERATE ALL FUNCTIONS FROM THE GROUND CONTROL STA-
TION ONLY.
1. Using all applicable safety precautions, activate the
hydraulic system.
2. When working on the platform slave level cylinder,
stroke the platform slave level cylinder forward until
the platform sits at a 45° angle.
3. Shut down the hydraulic system and allow the
machine to sit for 10-15 minutes. If the machine is
equipped with bang-bang or proportional control
valves, 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. If the machine is equipped with hydraulic con-
trol valves, move the control lever for the applicable
cylinder in each direction. This is done to relieve
pressure in the hydraulic lines. Carefully remove the
hydraulic hoses from the 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, the counterbalance valve
is defective and must be replaced.
5. To check the piston seals, carefully remove the
counterbalance valve from the retract port. After ini-
tial discharge there should not be any further leak-
age 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 the counterbalance valve and
carefully connect the hydraulic hoses to the cylinder
port block.
7. If used, remove the lifting device from the upright or
remove the prop from below the boom, activate the
hydraulic system and run the cylinder through one
complete cycle to check for leaks.