H
y
dra
u
lic
s
9803/
3280
Issue
1
Component Location
Component Key:
T
Hydraulic Tank
P
Hydraulic Pump (engine driven)
1A
Pump Outlet Pipe/Hose
3
Loader Valve Block
4
Excavator Valve
6
Return Line Filter (inside hydraulic tank)
13
Return Line Check Valve
26
Hydraulic Oil Cooler
Neutral Circuit Description
Variable Flow
The variable flow displacement pump
P
is mounted
on the rear of the gearbox and is engine driven via
a driveshaft.
With variable flow hydraulics, there is no ‘neutral’
circuit. This is because the pump
P
operates on a
d emand signal from t he servic es (see
Circuit
Descriptions, Hydraulic Pump - Variable Flow
Operation
). If there is no demand, then the pump
d oes not d raw oil from t he t ank and no oil is
delivered, there is no pump flow in the neutral
position.
When a service is selected, the pump senses the
demand and oil is drawn from the hydraulic tank
T
.
Pressurised oil from the pump flows to the loader
valve
3
and/or the excavator valve
4
via hose and
pipe assembly
1A
.
The loader valve
3
is fitted with a priority inlet
manifold, oil entering the loader valve is distributed
to the (priority) steer circuit and/ or the loader
services as required (see
Circuit Descriptions,
Loader Valve - Variable Flow Operation
).
Some of the exhaust oil flows directly back to the
tank through an in-tank filter
6
, and some of the
exhaust oil returns to tank via the hydraulic oil
cooler
26
.
To help prevent excavator dipper ram and loader lift
ram cavitation, there is a check valve
13
fitted to
t he ret urn line. The c hec k valve raises
approximately 5 bar (75 lbf/in
2
) of pressure in the
line, which improves the operation of the respective
anti-cavitation valves.
3 -
8
3 -
8
B
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