Operation - Hitachi ZW180 Technical Manual

OPERATION

At Neutral (Pusher Stroke: Between A and B)
1. At the neutral position of the control lever, spool
(7) completely blocks pressure oil of port P. As the
outlet port is connected to port T through the
notch part of spool (7), pressure at the output port
is equal to pressure in the hydraulic oil tank.
2. When the control lever is moved slightly, cam (1)
is tilted, and pusher (2) and spring guide (4) are
pushed in. Pusher (2) and spring guide (4) remain
mutually connected, move downward while
compressing return spring (6).
3. At this time, spool (7) is pushed by balance spring
(5) and moves downward until the clearance in
part A becomes zero.
4. During this movement, the output port remains
connected with port T and pressure oil is not
supplied to the output port.
NOTE: The lever stroke during the period when
part A becomes zero is the play of the
control lever.
During Metering or Pressure Decrease (In Pusher
Stroke: Between C and D)
1. When the control lever is further tilted, the hole
part on spool (7) is connected to notch part (B).
2. Pressure oil of port P flows into the output port
through notch part (B) and the hole part on spool
(7), and pressure at the output port is raised.
3. Pressure at the output port acts on the bottom of
spool (7) and tends to push spool (7) upward.
4. In case the force pushing spool (7) upward is
smaller than the spring force of balance spring (5),
balance spring (5) is not compressed. Therefore,
port P and the output port remain connected, and
pressure at the output port keeps rising.
COMPONENT OPERATION / Pilot Valve
5. When pressure at the output port rises further, the
force pushing spool (7) upward increases. If this
force becomes larger than the force of balance
spring (5),
compressing balance spring (5).
6. When spool (7) moves upward, notch part (B)
closes and pressure oil stops flowing from port P
to the output port. And pressure increase at the
output port is stopped.
7. In this way, balance spring (5) is compressed by
the amount spool (7) is pushed downward, and
pressure at the output port is the balanced
pressure acting on spool (7) and the spring force.
Pilot
Pressure
T3-6-14
spool (7) moves
D
C
A B
Pusher Stroke
Output Diagram
upwards by
T1F3-03-09-004