Hitachi ZW180 Technical Manual page 246

COMPONENT OPERATION / Steering Pilot Valve
Left Steering
1. When the steering wheel is turned to the left,
spool (4) rotates. Pressure oil from the brake/pilot
pump flows in the order of port P - sleeve (3) -
spool (4) - sleeve (3) - housing (1) - gerotor (8).
2. Pressure oil from gerotor (8) flows in the order of
housing (1) - sleeve (3) - spool (4) - sleeve (3) -
port L – the steering valve, and controls the
steering valve.
3. The steering valve operates the steering cylinder
by pressure oil from the main pump, and directs
the vehicle body toward left.
Steering Cylinder
Port R
Port T
4 2 3
Steering Pilot Valve
T3-4-4
4. Returning oil from the steering valve flows to port
R, flows in the order of housing (1) - sleeve (3) -
spool (4) - sleeve (3) - port T and returns to the
hydraulic oil tank.
5. When pressure oil from the brake/pilot pump flows
to gerotor (8), gerotor (8) rotates to the left.
Rotation of gerotor (8) is transmitted to sleeve (3)
via drive (7), and sleeve (3) rotates to the left.
6. When sleeve (3) rotates by the same amount of
spool (4), the passage between sleeve (3) and
spool (4) is closed and operation of the steering
valve is stopped.
7. Therefore, gerotor (8) rotates in response to
rotation of the steering wheel, and the steering
valve is operated in response to the amount of
turns of the steering wheel.
Steering Valve
Main Pump
Port L
Port P
Brake/Pilot
Pump
1
8
7
T4GB-03-04-009