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HYDRAULIC SYSTEM
CD5515-2/YB5515-2 SERVICE MANUAL
4-22
Published 1-20-2017, Control# 483-02
Load Holding Valves
The vertical (jack) cylinders have load holding valves
installed in the cylinder base. The purpose of these valves is
to inhibit the cylinder from retracting if a hydraulic line or
hose breaks. The load-holding valve will hold the oil in the
base of the cylinder until there is oil from the pump available
to the rod side of the cylinder.
Oil flows freely through the load-holding valve and into the
cylinder base when the cylinder is being extended. To retract
the cylinder, oil is sent to the rod port of the cylinder. As the
cylinder starts to retract, the piston meets resistance of the
oil held in the cylinder base by the load-holding valve.
Pressure increases as the pump tries to overcome the
resistance.
When the pressure on the oil from the pump is high enough
to overcome the spring in the load-holding valve plus the
pressure of the oil in the cylinder base, the load-holding
valve opens and the cylinder retracts.
If the cylinder starts to retract too rapidly, for example
because of a heavy load on the cylinder, pilot pressure from
the rod side decreases and the load holding valve closes.
The cylinder stops retracting temporarily until enough oil is
again available to the rod side of the cylinder. In this way,
cylinder cavitation is prevented and the load is held.
NOTE:
The engine must be running to retract the outrigger
cy lin ders . The loa d-holdin g v alv es preve nt
retracting the outrigger jacks simply from the
weight of the machine.
Vertical Outrigger Cylinder Leakage Check
If one of the outrigger vertical cylinders will not hold under
load, the problem is either the holding valve or the cylinder
piston packings. To check for internal leakage in the cylinder:
1.
Start the engine and engage the parking brake.
2.
Fully lower the outrigger.
3.
Shut off the engine.
4.
Remove the hydraulic line from the rod port of the
vertical cylinder being checked.
5.
Start the engine and actuate the control switch in the
direction to lower the outrigger. Check the amount of
leakage from the open port. If the leakage is more than a
couple of drops per minute, replacement of the piston
seals is recommended.
COMPONENT REPAIR
Hydraulic Pump Repair
Removal
1.
Drain the hydraulic tank.
2.
Remove the secondary pump from the primary pump.
See removal instructions.
3.
Disconnect the suction line and pressure line from the
primary pump. Disconnect the load sense and drain
lines from the pump. Cap and plug all hoses and ports.
4.
The pump is heavy. Use an overhead crane and a sling
or a support to hold the pump in position.
5.
Remove the pump mounting bolts and lockwashers.
Remove the pump and gaskets from the transmission.
Disassembly and Repair
The hydraulic pump is not a field repairable component. The
pump must be sent back to the pump manufacturer for
repair. Contact your distributor for return information.
Installation
1.
Attach the pump fittings to the pump before installing the
pump to transmission. Check the O-rings on the inlet
and outlet hose fittings. If damaged replace the O-rings.
2.
Align the spline of the pump shaft with the spline of the
pump coupler on the transmission. Position the pump
with the three gaskets. Install the mounting hardware.
3.
Install the secondary pump to the primary pump. See
installation instructions.
4.
Attach the suction and pressure hoses to the primary
pump.
5.
If a new pump is being installed, remove the two lower
hex-socket capscrews from the rear of the piston pump.
Discard the capscrews.
6.
Connect the load sense line to the pump compensator.
7.
Connect the pump drain line to the pump.
8.
Fill the hydraulic tank with clean filtered hydraulic oil.
NOTE:
The variable displacement pump and all other
components require clean, filtered hydraulic oil for
proper operation. Contaminated hydraulic oil may
cause damage to the pump and other components.
Before adding any oil to the hydraulic tank, be sure
it is filtered through a 10 micron (absolute) or less
filter.
9.
The pump will fill with hydraulic oil when the tank is filled.
The air in the pump will work itself back to tank.
10.
Perform pump start-up. See below.
Reference Only
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