JLG G12-55A Service Manual - Manual (Page 123)

8-3 G10-55A, G12-55A
Hydraulic System
8.2 SAFETY INFORMATION
Petroleum-based hydraulic fluids are used in this
machine. The temperature of hydraulic fluid increases
during operation of various hydraulic functions. A heated
petroleum-based hydraulic fluid presents a fire hazard,
especially when an ignition source is present. Hydraulic
fluid has a flash point that ranges from 300–600° F
(150–318° C) and an auto-ignition temperature of
500–750° F (262–402° C).
Accordingly, periodically inspect all hydraulic system
components, hoses, tubes, lines, fittings, etc. Carefully
examine any deterioration and determine whether any
further use of the component would constitute a hazard.
If in doubt, replace the component.
Operate the hydraulic controls after the engine has
stopped to relieve trapped pressure.
Note: Residual pressure may remain in hydraulic
cylinders, hoses, valve bodies, components, etc. If
hydraulic lines going to or coming from a component
are taut, slowly and cautiously relieve (“bleed off”)
the pressure.
Whenever you disconnect a hydraulic line, coupler, fitting
or other component, slowly and cautiously loosen part
involved. A hissing sound or slow seepage of hydraulic
fluid may occur in most cases. After hissing sound has
ceased, continue removing the part. Any escaping oil
should be directed into an appropriate container. Cap or
otherwise block off part to prevent further fluid seepage.
Hydraulic system maintenance will, at times, require that
engine be operated. Always follow safety precautions.
A major cause of hydraulic component failure is
contamination. Keeping hydraulic fluid as clean as
possible will help avoid downtime and repairs. Sand, grit
and other contaminants can damage finely machined
surfaces within hydraulic components. If operating in an
exceptionally dirty environment, change filters and
inspect fluid more often. When servicing system, cap or
plug hydraulic fittings, hoses and tube assemblies. Plug
all cylinder ports, valves and the hydraulic reservoir, and
pump openings until installation occurs. Protect threads
from contamination and damage.
Some hydraulic functions are actuated by interfacing with
electrical system components (switches, solenoids and
sensors). When the hydraulic system is not functioning
properly, check the electrical aspect of the malfunctioning
circuit also. Refer to Section 9.5, “Electrical System
Schematics,” in this manual.
8.3 HYDRAULIC PRESSURE DIAGNOSIS
JLG Parts Department has a kit available to use for
hydraulic system maintenance and troubleshooting: the
JLG Pressure Test Kit. The kit is contained in a durable
polyethylene carrying case for demanding field service
conditions.
Hydraulic Pressure Test Kit
The hydraulic pressure test kit is used to pressure test the
various hydraulic components in the hydraulic system.
The kit includes:
• Gauges for testing high and low pressure circuits
• Fittings, couplers and hoses
Contact JLG Parts Department Toll Free at
1-877-554-5438 or 717-485-6472 for ordering information.
WARNING
DO NOT service the machine without following all
safety precautions as outlined in Section 1, “Safety
Practices,” of this manual.
Part
Number
Description
Approximat
e
Weight
Price and
Availability
70000652
Dial Hydraulic Pressure
Test Kit
10 lbs. Consult Factory
70000101
Digital Hydraulic Pressure
Test Kit
7 lbs. Consult Factory
70027911
Digital Hydraulic Pressure
Test Kit
7 lbs. Consult Factory