Lull 944E-42 Service Manual - Manual (Page 307)

8.55 Model 644E-42/944E-42 Rev. 6/04
Hydraulic System
8.8 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
problems that can occur during the operation of the
hydraulic system. Electrical and hydraulic functions are
often related. Verify that the electrical components of the
circuit are functioning properly whenever troubleshooting
the hydraulic circuit.
Always check the following before beginning to
troubleshoot 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.
3. Check for air in the hydraulic system. Erratic
machine performance and/or spongy cylinder
operation are signs of air in the hydraulic system.
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.
WARNING:
Wait for hydraulic fluid to
cool before servicing any hydraulic component.
Hot hydraulic fluid can cause severe burns.
WARNING:
Relieve hydraulic pressure
before servicing any hydraulic component.
Escaping hydraulic fluid under pressure can
penetrate the skin causing death or serious
injury. When checking for air in the hydraulic
system, wear safety glasses and gloves to help
provide protection from spraying hydraulic oil.