Hydraulics
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
demand signal from the services (see Circuit
Descriptions, Hydraulic Pump - Variable Flow
Operation). If there is no demand, then the pump
does not draw oil from the tank 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
the return line. The check 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
Basic System Operation
Section E Section E
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