Operation and maintenance manual

Section 250-0075
3
SM 2161 7-02
PRIORITY UNLOADER VALVE FAULT DIAGNOSIS
CONDITION REASON ACTION
Rapid switching of High leakage in brake circuit. Check brake circuit for leakage.
unloader relief valve.
Internal leakage to priority Replace priority unloader valve assembly.
unloader valve.
Check valve leaking or not Replace priority unloader valve assembly.
seating properly.
Circuit does not load or Unloader relief valve sticking. Replace priority unloader valve assembly.
unload.
Worn or damaged unloader Replace priority unloader valve assembly.
relief valve.
Braking System - Priority Unloader Valve
ports and orientation.
INSTALLATION
Numbers in parentheses refer to Fig. 1.
Note: Tighten all fasteners to standard torques listed
in Section 300-0080, STANDARD BOLT AND NUT
TORQUE SPECIFICATIONS.
Note: Tighten all hydraulic lines fitted with ORFS
connections, as described in Section 250-0000,
BRAKING SYSTEM SCHEMATIC. Renew all 'O' rings
where used.
1. Secure priority unloader valve to hydraulic cradle
with bolts and lockwashers.
2. Remove blanking caps from hydraulic lines and
install lines to the priority unloader valve as identified
during removal.
3. Fill hydraulic oil tank with hydraulic oil as specified
in Section 300-0020, LUBRICATION SYSTEM. Refer
to Section 230-0040, HYDRAULIC TANK, for hydraulic
oil levels. Install filler cap on hydraulic tank filler neck.
4. Place the battery master switch in the 'On' position,
start the engine and bring hydraulic oil to operating
temperature.
5. Check priority unloader valve and hydraulic line
connections for leaks and tighten as required.
6. Remove all blocking from road wheels and place
steering lock bar in the stowed position.
FAULT DIAGNOSIS
Refer to following fault diagnosis chart. As stated
previously, it is not recommended that any of the
cartridge assemblies are disassembled for
maintenance purposes. Ensure that valve assembly is
cleaned off prior to removal of any components and
that no contaminant is allowed to enter the internal
galleries.
If investigation shows that the cartridge assemblies
are in good clean condition and fit for use, the seals
should be replaced prior to re-assembly. Damage to
the cartridge assemblies or valve body would
necessitate a new priority unloader valve assembly.
SPECIAL TOOLS
There are no special tools required for procedures
outlined in this section. Refer to Section 300-0070,
SERVICE TOOLS, for part numbers of general service
tools required. These tools are available from your
dealer.
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