Hydraulic Circuits And Troubleshooting - JLG sky trak mmv Service Manual

9.8 HYDRAULIC CIRCUITS AND
TROUBLESHOOTING
This section covers the hydraulic circuits and includes a
circuit drawing, troubleshooting chart, and description of
the circuit for each function.
Typically, the circuit drawings illustrate the flow of oil for
the hydraulic function being shown.
The troubleshooting charts cover some common prob-
lems that can occur during the operation of the hydraulic
system. Electrical and hydraulic functions are often relat-
ed. Verify that the electrical components of the circuit are
functioning properly whenever troubleshooting the hy-
draulic circuit.
Always check the following before beginning to trouble-
shoot a circuit that is not functioning correctly.
1. Check the hydraulic oil level in the reservoir. Oil level
should be in the middle of the sight glass with all
cylinders retracted.
2. Check hoses, tubes, fittings and other hydraulic
components for leaks, bends, kinks, interference,
etc.
Model MMV Rev. 12/04
3. Check for air in the hydraulic system.
Erratic machine performance and/or spongy cylinder
operation are signs of air in the hydraulic system.
WARNING:
cool before servicing any hydraulic component.
Hot hydraulic fluid can cause severe burns.
WARNING:
sure before servicing any hydraulic compo-
nent. Escaping hydraulic fluid under pressure
can penetrate the skin causing death or seri-
ous injury. When checking for air in the hydrau-
lic system, wear safety glasses and gloves to
help provide protection from spraying hydraulic
oil.
If air in the hydraulic system is suspected, you will
hear air leakage when hydraulic fittings are loosened
and see air bubbles in the hydraulic fluid.
Loose fittings, faulty o-rings or seals, trapped oil,
leaks, system opened for service, etc., can cause air
in the system. Determine what is causing air to enter
the system and correct it. Bleed air from the system.
Hydraulic System
Wait for hydraulic fluid to
Relieve hydraulic pres-
9.13