9803/3280
Issue 1
6 - 1
6 - 1
Circuit Descriptions
Section E
Section E
Loader Valve - Neutral Circuit
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
The loader valve is mounted on the chassis frame, right
hand side (when viewed from the rear).
It includes the lift ram spool
3C
, shovel ram spool
3D
and
auxiliary spool
3E
. Linkage rods connect the spool ends to
the control levers.
In neutral circuit hydraulic oil from the pump section
P2
enters the loader valve at
1C
via the steering priority valve
.
On entering the valve block, oil flows around the waisted
section of the unloader valve
3L
, past check valve
3N
and
joins the flow from pump section
P1
.
Oil from pump section
P1
enters the loader valve at
1A
.
Combined oil flow from
P1
and
P2
passes the main relief
valve (MRV)
3B
and fills the parallel gallery
B
. From the
parallel gallery the oil flows around the waisted central
portions of spools
3C
,
3D
and
3E
(all in neutral position) and
flows on to feed the excavator valve via high pressure carry
over line
1B
.
Pressure in inlet gallery
C
is sensed by pilot valve
3M
via the
bore of spool
3L
. At pressures below the setting of the
unloader valve, both pilot valve
3M
and spool
3L
remain
closed.
Loader Valve - Unloader Operation
Unloader spool operation protects the engine from being
overloaded if a service is being worked particularly hard, for
example when using the excavator to tear out. It does this
by dumping the oil from the pump section
P2
to tank,
allowing engine power to be applied fully to the main pump
section
P1
.
If the pressure in the inlet gallery
C
rises to the setting of the
pilot valve
3M
, this valve will open, allowing oil in spring
cavity
3P
to escape more quickly than it can be replaced by
oil entering through the small drilling
D
.
This creates a pressure differential between the spring cavity
3P
and gallery
C
. Higher pressure in gallery
C
acts on the
face of spool
3L
causing the spool to be moved off its seat.
Oil entering the valve block from pump section
P2
now flow
directly to tank
T
.
High pressure in gallery
C
also holds check valve
3N
firmly
closed, preventing oil from pump section
P1
from also being
dumped.
When pressure in inlet gallery
C
falls, for example if the
excavator has stopped tearing out, pilot valve
3M
will close.
This means oil in spring cavity
3P
will be at the same
pressure as oil in gallery
C
, spring pressure will move spool
3L
back onto its seat, closing pump section
P2
connection
to tank.