Gradall LOED 534A Service Manual - Manual (Page 33)

The design and construction of the HUSCO Model 5000
Sectional Valve allows for easy service or replacement of
the various sections, seals and components. All parts are
available for replacement with the exception of furnishing
separately either the plunger housing or the plunger. They
are selectively fit and are available as a complete unit.
Should either require repair, it will be necessary to return
the complete plunger section.
To perform service operations, it is recommended that the
valve be removed from the machine. However, in some
instances, it is only necessary to remove the parts or
sections requiring service or replacement. In either case,
the exterior of the valve must be thoroughly cleaned
before disassembly.
MAINTENANCE PROCEDURE
Valve Disassembly
Remove tie rod nuts from one side of valve and carefully
slide valve sections across tie rods to avoid losing circuit
check poppet and spring, which is enclosed between plunger
sections. This poppet must be kept with respective plunger
section and should be tagged. An O-ring is also present
between the sections, and can be removed. When separating
sections, extreme care must be exercised not to damage
machined sealing surfaces. Place section on a clean
surface.
Plunger End Seals
An O-ring plunger seal, protected by a one piece molded
wiper, is used at each end of the plunger. To replace them,
remove the seal plates und plunger control from the cap
end. After seals are removed, inspect seal counterbores so
that surfaces are smooth and completely free of dirt, pits
rust, and metal particles. Select new seal and wiper and coat
them with hydraulic oil. Thoroughly clean seal counterbore
in housing and install O-ring, followed by wiper. Install
seal plates and plunger controls.
If for some reason, it is necessary to remove plungers, they
should be tagged for their respective plunger sections.
Switching them will result in incorrect clearances, causing
either binding and sticking or excessive leakage.
Circuit Check Valves
The circuit check valves are of the poppet type and are
spring loaded. They are retained in one side of the machined
surface of each plunger section and normally require very
little service.
HUSCO MODEL “5000” SECTIONAL VALVE
SERVICE INFORMATION
Check valve malfunctioning is usually the result of foreign
matter lodging between the seat and the poppet. Examine
seat for dirt or metal particles. Check seating face for
nicks or scratches and, if present, they can be removed by
lapping, using fine lapping compound; however, care must
be exercised to prevent lapping compound from entering
or remaining in valve. Examine spring and replace if it is
w e a k , b r o k e n , o r d i s t o r t e d .
Section Seal
All machined surfaces between inlet and outlet sections
(which includes plunger sections) are ground and must be
free of dirt or any raised burrs. If present, they must be
removed by lapping on a perfectly smooth flat steel
surface using fine lapping compound. Clean section very
thoroughly to avoid lapping compound from remaining
in any of the valve passages.
Examine machined O-ring counterbore so that surfaces are
smooth and completely free of dirt, pits, rust, and metal
particles. Select new O-ring and, after thoroughly cleaning
counterbore, install it.
Assembling Sections
Place the various sections in the proper order, making
certain the circuit check poppet and spring are positioned.
properly in the plunger section, and install the tie rods. The
top one is 3/8 dia. and the others 5/16 dia. Assemble the
nuts and, using a torque wrench, apply 33 ft. lbs. of torque
to the top one and 14 ft. lbs. to the others.
Cartridge Main Relief
See service information Page 4 in this section.
TESTING PLUNGER LEAKAGE
To check the leakage rate of the plungers, install a good accurate
pressure gauge in the cylinder port that is controlled
by the plunger to be tested. Actuate the plunger until full
relief valve pressure is indicated on this gauge. Return
plunger to neutral. The rate at which the pressure drops
is an indication of the leakage past the plunger. The rate of
drift of the cylinder is also an indication. Care must be
exercised in interpreting these results, as leakage past the
cylinder packings is also included in these determina-
t i o n s .
TESTING CIRCUIT CHECK VALVE
The circuit check valves can be tested in a similar manner
With full relief pressure in the cylinder port and the plunger
in the operating position, stop the pump and check the
rate of pressure drop in the cylinder port. It must be noted
that this pressure drop reflects no
t only the leakage past
the check valve and cylinder packing but also the leakage
around the plunger.
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