Lull 944E-42, Service Manual

Page: 331 / 844

8.81 Model 644E-42/944E-42 Rev. 6/04
Hydraulic System
NOTE:
When checking pressures in
circuits, refer to Section 8.7,
“Hydraulic System Testing,” for
correct pressure readings.
Not
OK
Check seals on extend/retract cylinder. Repair/replace extend/retract
cylinder.
If OK
If OK
Not
OK
Check counterbalance valve on
extend/retract cylinder.
Replace the counterbalance
valve.
Not
OK
Check pilot operated check valve on
extend/retract cylinder.
Replace the pilot operated
check valve.
If OK
Not
OK
The extend/retract cylinder does not
retract.
Check the standby pump pressure at
implement pump pressure tap.
Replace unloader cartridge
on main control valve.
If OK
Not
OK
Check pilot pressure at “PPG” port of
accumulator charge/secondary
function valve.
Adjust/repair/replace
pressure reducing cartridge
on accumulator charge/
secondary function valve.
If OK
Not
OK
Adjust/replace main relief
cartridge on main control
valve.
If OK
Not
OK
Repair/replace joystick.
Check the main relief pump pressure
at implement pump pressure tap.
Refer to Section 8.7, “Hydraulic
System Testing,” test sequence 7.
Not
OK
Not
OK
If the extend/retract
cylinder drifts or reacts
slowly, check the seals on
the extend/retract cylinder.
Replace counterbalance and/
or pilot-operated check valves
on the extend/retract cylinder.
Check counterbalance and
pilot-operated check valves.
Repair/replace extend/retract
cylinder.
If OK
Install pressure gauge in the pilot
supply line, between the joystick &
pilot select valve and pilot select valve
& extend/retract section of main
control valve. Check pilot pressure.
With the joystick moved all the way to
the left, the pressure should be
444 ±22 psi (30,6 ±1,5 bar).
Before troubleshooting any
hydraulic circuit, ALWAYS
begin by checking the
following:
1. Hydraulic oil level in the
reservoir
2. All hoses, tubes, fittings
for leaks, kinks,
interference, etc.
3. Air in the lines