Hitachi ZW180 Technical Manual page 254

COMPONENT OPERATION / Steering Valve
When Steering Left
1. When the steering handle is turned to the left, pilot
pressure oil is supplied to port Pb from the
steering pilot valve and spool (1) moves to the
right.
2. Pressure oil from the main pump is supplied to the
steering valve from port P, and supplied to
passage A (7) through variable orifice (5).
3. Pressure oil in passage A (7) pushes and opens
load check valve (4) and flows to the steering
cylinder through port B.
4. Returning oil from the steering cylinder enters
spool (1) through port A and returns to the
hydraulic oil tank through port T.
5. Pilot pressure oil flowing into port Pb pushes spool
(1) at the port Pb side and flows to port Pa after
being reduced by fixed orifice (6) at the same time.
This reduces the shock caused by fast operation
of the handle. (Refer to the Layout on T3-5-2 and
the Steering Circuit in the SYSTEM / Hydraulic
System group.)
NOTE: Opening area of variable orifice (5) is
proportional to the stroke amount of spool
(1) due to pilot pressure from the steering
pilot valve. (Refer to the Steering Circuit in
the SYSTEM / Hydraulic System group.)
T3-5-6