Spool and Sleeve
(1) Inner spool. (10) Pin. (15) Slots for centering springs. (16)
Outer sleeve. (17) Grooves for oil flow. (18) Holes for pin.
(19) Small holes for oil flow.
When the steering wheel is turned, spool (1), pin (10), and
drive (8) start to turn. Sleeve (16) does not turn at the same
time as the spool (1) because the diameter of holes (18) in the
sleeve (16) are slightly larger than the diameter of pin (10).
Consequently, spool (1) turns inside sleeve (16) enough to
align small holes (19) in sleeve (16) with grooves (17) in spool
(1). The alignment of these holes and grooves provides the
path for oil flow to the gerotor. The oil now flows to the
steering cylinder. Centering springs (9) are compressed when
the spool moves in relation to the sleeve. When the steering
wheel is no longer turning, the springs bring the spool and the
sleeve back to a center position.
The front end of the machine stays in the turned position when
the steering stops. The steering wheel must be turned in the
opposite direction in order to straighten the machine.
When the machine is off, the metering pump can be manually
operated. The metering section (B) operates as a pump. The
suction of the metering section opens the internal check valve
(11). When the internal check valve opens, return oil flows
from the steering cylinder to the inlet side of the metering
section. During power operation, supply pressure keeps the
check valve closed.
The internal check valve (11) converts the metering pump into
a hand operated pump for limited manual steering.