Operation - Hitachi ZW180 Technical Manual

OPERATION

At Neutral
1. At neutral, spool (7) completely blocks pressure
oil of port P. The output port is connected to port T
through the fine control hole on spool (7).
Therefore, pressure at the output port is equal to
pressure at port T.
2. If the control lever is slightly tilted, disc (1) is tilted,
and push rod (2) and piston (3) are pushed in.
Piston (3) pushes spring guide (4) and balance
spring (5) downward, and moves downward.
3. At this time, spool (7) is pushed by balance spring
(5), and moves downward until the clearance at
part A becomes zero.
4. During this movement, the output port remains
connected to port T and pressure oil is not
supplied to the output port.
NOTE: The lever stroke during the period when
clearance (A) becomes zero is play of the
control lever.
COMPONENT OPERATION / Pilot Valve
T3-6-8