7 - 4
Loader Valve - Variable Flow
Auxiliary Spool
The auxiliary valve section comprises the spool assembly A,
load hold check valve assembly B, primary and secondary
shuttles, items L and K respectively.
While the spools are in neutral position, the primary shuttles
and secondary shuttles are vented to tank. When a spool is
operated, the load pressure sensed at the work port is
directed via the primary and secondary shuttles to the
hydraulic pump, where the pump subsequently ‘swashes’
and increases its output to meet this load sense demand.
When a service is selected (the spool moved up or down),
the waisted sections of the spool connect passage C to one
of the service ports D. Oil from the pump must overcome the
force of spring E to lift poppet F and make the connection
from the pump passage J to the service ports D via passage
C.
In some instances there is a back pressure in the service line
(e.g. generated by the weight of a loaded shovel). This
pressure is felt in chamber G via drilling H in poppet F. The
back pressure combined with the force of spring E keeps
the load hold check valve firmly closed, preventing the load
from dropping.
The pressure in pump passage J will increase until it is
greater than that in the service line. At this point, the load
hold check valve will open, as previously described.
Section E
Hydraulics
9803/3280
Section E
7 - 4
Issue 1
Circuit Descriptions
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