Lull 944E-42 Service Manual - Manual (Page 341)

8.89 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 lift/lower cylinder. Repair/replace lift/lower
cylinder.
If OK
If OK
Not
OK
Check counterbalance valve on lift/
lower cylinder.
Replace the counterbalance
valve.
Not
OK
Check pilot operated check valve on
lift/lower cylinder.
Replace the pilot operated
check valve.
If OK
Not
OK
The lift/lower cylinder does not
lower.
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.
Install pressure gauge in the pilot
supply line, between the rear
joystick and the extend/retract
section of main control valve.
Check pilot pressure. With the
joystick moved all the way to the
right, the pressure should be
444 ±22 psi (30,6 ±1,5 bar).
Check the main relief pump
pressure at implement pump
pressure tap. Refer to Section 8.7,
“Hydraulic System Testing,” test
sequence 7.
Install pressure gauge in the pilot
supply line, between the joystick &
pilot select valve and pilot select
valve & lift/lower section of main
control valve. Check pilot pressure.
With the joystick moved all the way
forward, the pressure should be
444 ±22 psi (30,6 ±1,5 bar).
Not
OK
Not
OK
If the lift/lower cylinder
drifts or reacts slowly,
check the seals on the lift/
lower cylinder.
Replace counterbalance and/
or pilot-operated check valves
on the lift/lower cylinder.
Check counterbalance and
pilot-operated check valves.
Repair/replace lift/lower
cylinder.
If OK
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