Hitachi ZW180 Technical Manual page 318

COMPONENT OPERATION / Drive Unit
Operation
During Operation
The clutch is operated by pressure oil from the
transmission control valve.
Pressure oil from the transmission control valve
reaches the back of clutch piston (7) through the oil
passage inside shaft (11). The oil passage is blocked
as pressure oil pushes bleed valve (5) in clutch piston
(7) toward disc (8). Therefore, clutch piston (7) is
pushed toward disc (8). Clutch piston (7) transmits
power to the whole of shaft (11) and hub gear (1)
connected by pushing disc (8) and plate (9) tightly.
Not during Operation
When pressure oil is not supplied from the
transmission control valve, bleed valve (5) is opened
by the centrifugal force of shaft (11). Therefore, the
risidual pressure in the piston and others are
discharged toward disc (8). Clutch piston (7) is
pushed back by return spring (3) between plates (9).
As there arises a clearance between disc (8) and
plate (9), shaft (11) and hub gear (1) rotate separately,
and power is not transmitted.
T3-9-12