9803/3280
Issue 1
6 - 4
6 - 4
Circuit Descriptions
Section E
Section E
Loader Valve
- Hydraulic Speed Control (HSC)
Solenoid valve
3Q
allow s t he op erat or t o c ont rol t he
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