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(1) Spool operation (take the tilt spool
valve for example)
a) Neutral position (See Fig. 5-4)
The high-pressure oil from lift pump
returns to the oil tank through the
mid-passage.
Fig. 5-4 Neutral position
b) Pushing-in of spool (See Fig. 5-5)
In this time, the spool is pushed in to
close the mid-passage. This causes the oil
from the main oil-inlet to push up the inlet
check valve and to flow into the port “B”.
The return oil from the port “A” flows
through the low-pressure passage to the
tank and the spool is restored to its neutral
position by the return spring.
Fig. 5-5 Push in spool
c) Drawing-out of spool (See Fig. 5-6)
With the mid-passage closed, the oil
from the main oil-inlet pushes up the
check valve and flows into the port “A”.
The return oil from the port “B” flows
through the low-pressure passage to the
tank. The spool can be restored to its
neutral position by return spring.
Fig. 5-6 Draw out spool
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