STEERING CONTROL VALVE
STEERING CONTROL VALVE IN NEUTRAL POSITION
1. Tank return passage.
11. Outlet to cylinders
(for left turn).
14. Outlet to cylinders
(for right turn).
3. Outlet to tank.
8. Outer spring.
15. Ball resolver valve.
4. Flow control valve.
9. Inner spring.
13. Narrow slots.
5. Pilot valve.
10. Wide slots.
When there is no force on the steering wheel,
springs (8) and (9) keep spool (6) in the NEUTRAL
position. Oil from the hydraulic pump flows into the
control valve through inlet (2). The flow of oil to the
cylinders is stopped by spool (6). This causes an
increase in the pressure of the oil in the inlet passage,
and flow control valve (4) opens. The valve opens until
the oil from the pump can flow through the holes in the
flow control valve. The oil then flows through outlet (3)
and back to the hydraulic tank.
In the NEUTRAL position, the valve spool also
blocks (stops) the oil in the lines to the cylinders. This
holds the machine in the turned position where the
steering wheel was stopped. A very small amount of oil
can flow to and from the steering cylinders through slots
(13). This reduces the shocks caused when the wheels
come in contact with an object.
The pressure of the oil in the blocked outlets (11)
and (14) is felt through passages (12) and (16) and
against pilot valve (5). If an outside force tries to turn
the machine when the valve spool is in the NEUTRAL
position, the increase in pressure is felt against pilot
valve (5). The pressure will not go higher than 2000 ±
25 psi (140.6 ± 1.8 kg/cm2) (13 790 ± 172 kPa).