Case 580SR, Service Manual

Page: 614 / 1068

24 SECTION 35 - HYDRAULIC SYSTEM
3. CONTROL VALVES
3.1 CONTROL VALVES “REXROTH” (MECHANICAL MODELS)
The hydraulic circuit is a load sensing flow sharing
system working in conjunction with a fixed displace-
ment gear type hydraulic pump.
This system has the advantage that at any time the
distribution of flow to the services being operated is
in proportion to the openings of the control valve
spools.
The flow distribution to the backhoe and loader con-
trol valves is independent of the load and it is there-
fore possible to operate two or more spools
satisfactorily at the same time.
The principal components of the load sensing flow
sharing system are the pressure compensator
valves in each control valve section, together with
the load sense line which connects all the spool sec-
tions in both the loader and backhoe control valve
assemblies.
Because the hydraulic pump is a fixed displacement
gear type pump it should be noted that the load
sense line only connects the loader and backhoe
control valve assemblies and does not have any
connection to the hydraulic pump.
The hydraulic pump draws oil from the tank and flow
from the front pump is directed to the centre galler-
ies of the loader and backhoe control valves assem-
blies.
The flow coming from the rear section of the pump
passes through the load sensing flow divider valve
mounted on the pump and sends the priority flow to
the steering system, while the remaining flow adds
to the flow from the front pump, directed to the load-
er and backhoe attachment systems.
The centre gallery of both the loader and backhoe
control valves are blocked by the end plate.
Pressure in the supply system is controlled by the
pump flow balancer valve in accordance with the
pressure in the load sensing line.
Consequently the higher the load sense pressure
the less flow is returned to tank with corresponding
increase in flow/pressure to the hydraulic circuits.
Maximum system pressure is limited by the load
sense pressure relief valve which relieves pressure
in the load sense line when it reaches 210 bar.
Because the pump flow balancer valve is influenced
by load sense pressure the valve diverts sufficient
flow back to tank to maintain the maximum system
pressure of 210 bar. Loader attachment control valve
The loader control valve is mounted on the right
hand side of the machine adjacent to the pump.
The valve assembly consists of a maximum of three
spool operated sections and provides oil flow to the
loader boom, bucket and auxiliary services where
fitted.
Backhoe attachment control valve
The backhoe control valve is located at the rear of
the chassis.
The control valve consists of a maximum of seven
sections of spool control valves and provides the oil
flow for operating the lifting, the digging, the bucket,
the stabilizers, the swing and telescopic arm (op-
tional).
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