IV-72
HYDRAULIC UNITSPILOT VALVE
OPERATION
The pilot valve casing contains a vertical shaft hole
with a reducing valve incorporated into it. When
the handle is tilted, the push rod and spring seat
are pushed down changing the secondary pressure
spring·s pressure.
The casing also contains an inlet port for hydrau-
lic oil port P (primary pressure) and an outlet port,
port T (tank) and secondary pressure is taken from 4
ports, port 1, port 2, port 3 and port 4, on the bottom
of the vertical shaft hole.
When the Handle is in Neutral
In this case, the force of the secondary pressure set-
ting spring, which determines the pilot valve·s out-
put pressure (secondary pressure), is not transmitted
to the spool. Therefore, the spool is pushed up by
the return spring and is in the output port C position
shown above, with oil not flowing between port P
and the output port C but flowing between the T port
and output port C.
When the Handle is Tilted
When the handle (1) is tilted and the push rod is
pushed, the spool moves downward and port P and
port A are joined. The oil in the pilot valve pump
flows out to port A, generating pressure.
a. When the pressure in port A is the same as the
set force of the spring (set pressure), there is a
balance between the hydraulic pressure and the
spring force.
b. When the pressure in port A is greater than the set
pressure, port A and port P close and port A and
port T open.
c. When the pressure at port A is lower than the set
pressure, port A and port P open and port A and
port T close.
In this way, the secondary pressure is kept constant.
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