Lull 944E-42 Service Manual - Manual (Page 433)

8.181 Model 644E-42/944E-42 Rev. 6/04
Hydraulic System
Mono Block Disassembly
The mono block section (1) contains the relief valves,
spools and compensators for the attachment tilt (2),
frame sway (3), boom lift/lower (4) and boom extend/
retract (5) functions.
1. Remove the relief valves (6) from the appropriate
function. Remove and discard all seals.
Note: The internal parts of the relief valves are not
serviceable. Replace the entire relief valve if necessary.
2. Remove the hex socket head capscrews (7) holding
the spool end housings (8) to the mono block.
Remove the housings, o-rings (9), springs (10) and
pistons (11). Discard the o-rings.
Note: The individual spools in the mono block are not
serviceable separately. If a spool is scratched or nicked
the entire mono block must be replaced.
3. Remove the hex plug (12) and o-ring (13) from the
top of the individual functions. Discard the o-ring.
The two plungers (14) of each compensator are not
serviced separately. If these parts require
replacement the entire mono block has to be
replaced.
4. Remove the spring (15) from between the plungers.
c. Main Control Valve Parts Cleaning
Clean all components with a suitable cleaner, such as
trichlorethylene, before continuing. Blow dry.
d. Main Control Valve Parts Inspection
Inspect all parts and internal passageways for wear,
damage, etc. If inner surfaces of any component DO NOT
display an ultra-smooth, polished finish, or are damaged
in any way, replace the damaged part. Often, dirty
hydraulic fluid causes failure of internal seals, damage to
the polished surfaces within the component, and wear of
and/or harm to other parts.
Carefully remove the spools from each section and
inspect for contamination, scratches, scoring or
discoloration. If any damage is noted the sections with
spools must be replaced as a complete assembly. The
spools are not serviced separately.
Carefully remove the compensator plungers from each
section and inspect for contamination, scratches, scoring
or discoloration. If any damage is noted the sections with
compensators must be replaced as a complete
assembly. The compensator plungers are not serviced
separately.
e. Main Control Valve Assembly
Note: ALWAYS replace seals, o-rings, gaskets, etc.,
with new parts to help ensure proper sealing and
operation. Lubricate seals and o-rings with clean
hydraulic oil.
Mono Block Assembly
1. Install the spring (10) and plunger (11) into the spool
end housing (8). Place the spool end housing with a
new oiled o-ring (9) into position on the end of the
spool. Be sure the spool end housing rests square
on the side of the mono block (1). Secure the spool
end housing in place with the two hex socket head
capscrews (7). Torque the capscrews to 7 ±1 lb-ft
(9,5 ±1,4 Nm). Repeat for the other spool end
housings on the mono block.
2. Install the appropriate relief valves (6) into the
appropriate function. The two relief valves for the
attachment tilt section are preset to 4000 psi (276
bar). The relief valve in the extend/retract section is
preset to 2900 psi (200 bar). Torque the relief valves
to 33 ±3.5 lb-ft (45 ± 4,8 Nm). Use new seals when
installing the relief valves, refer to the Parts Manual
for seal kits.
3. Place the lower compensator plunger (14) followed
by the spring (15) and the upper compensator
plunger (16) into the cavity on the top of the mono
block (1). Secure in place with the hex plug (12) and
new oiled o-ring (13). Torque the plug to 48 ±5 lb-ft
(65 ±7 Nm). Repeat for the other compensators on
the mono block.