Operation - Hitachi ZW180 Technical Manual

OPERATION

The head of spool (6) is supported by the top surface
of spring guide (3). Spring guide (3) is lifted up by
return spring (5).
At Neutral (Output Diagram: Between A and B):
1. At neutral, spool (6) completely blocks pressure
oil of port P (from the pilot pump). As the output
port is connected to port T (to the hydraulic oil
tank) through the internal passage of spool (6).
2. Therefore, pressure at the output port (to the
control valve) is equal to pressure at port T.
3. When the control lever is tilted slightly, cam (1) is
tilted, and pusher (2) is pushed in. Pusher (2) and
spring guide (3) remain mutually and moves
downward while compressing return spring (5).
4. At this time, as pressures at the output port and
port T are equal, so spool (6) moves downward
with the bottom surface of its head keeping
contact with spring guide (3) by the force of
balance spring (4).
5. This condition continues until hole part (7) on
spool (6) is connected to port P.
COMPONENT OPERATION / Pilot Valve
Pilot
Pressure
T3-6-18
E
D
C
A B
Lever Stroke
Output Diagram
F
T523-02-05-001