Hydraulics
9803/3280 Issue 1
6 - 4 6 - 4
Circuit Descriptions
Section E Section E
Loader Valve
- Hydraulic Speed Control (HSC)
Solenoid valve 3Q allows the operator to control the
unloader spool movement (to dump flow from the hydraulic
pump section P2) using a switch. There are two main
applications for this operation:
1 More tractive force can be applied to the loader end
when entering a stock pile. This is because more power
is available from the engine as flow from pump section
P2 is being dumped directly to tank.
2 More power can be made available from the engine
whilst the machine is travelling on the highway. Again,
this is because flow from pump section P2 is being
dumped directly to tank.
When the solenoid valve 3Q is de-energised its spool is
moved by spring pressure. This spool movement makes a
connection from the unloader spool chamber 3P to tank.
Because the unloader chamber is now connected to tank,
and so at exhaust pressure, pressure in gallery C (neutral
shown) acts on the face of unloader spool 3L causing the
spool to be moved off its seat. Oil entering the valve block
from pump section P2 now flows directly to tank.
When solenoid valve 3Q is energised its spool closes the
connection from the unloader valve spool chamber to tank.
Spool 3L is once again controlled by system pressure.
Component Key:
B Parallel gallery
C Gallery
D Drilling
T Tank Port
1A Pump Inlet (section P1)
1B High Pressure Carry Over
1C Pump Inlet (section P2)
3B Main Relief Valve
3C LIft Ram Spool
3D Shovel Ram Spool
3E Auxiliary Spool
3L Unloader Valve Spool
3M Unloader Pilot Valve
3N Check Valve
3P Spring Cavity
3Q Solenoid Valve
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