S T E E R I N G S Y S T EM
A M P L I F I E D S T E E R I N G S Y S T EM
The steering wheel is connected to spool (1) by a
shaft assembly and splines. When the steering wheel
is turned, spool (1) turns a small amount until springs
(7) are compressed. Then sleeve (2) starts to turn. As
long as the steering wheel is turned, the spool and
sleeve both turn as a unit, but they turn a few degrees
When the spool and sleeve are a few degrees apart,
oil passages are opened between them. This lets the
pump oil from inlet (4) flow through passages in
body (11) to the metering section.
When the steering wheel is turned, pin (8) turns
with the sleeve and causes drive (12) to turn also. The
drive causes a rotation of gear (5) inside gear (6).
This rotation of the gear sends a controlled (metered)
flow of pilot oil back through body (11). This oil
flows to port (9) or (10) and then to the neutralizer
valve. Port (9) or (10), that is not used for pilot oil, is
used for return oil from the other end of the control
If the steering wheel rotation is stopped, springs
(7) will move sleeve (2) back in alignment with spool
(1) (NEUTRAL position). This will close passages
between the metering section and control section and
the HMU will be in the NEUTRAL position.
For the following paragraphs on this page, refer to the
illustration on page 3-62.
When the engine is running, a check valve prevents
pump oil at inlet (4) from flowing to outlet (3) then to
tank. But, if the pilot section of the oil pump fails while
S Y S T E M S
O P E R A T I O N
P U M P G E A R S I N M E T E R I N G S E C T I O N
5. Internal pump gear. 6. External pump gear. 8. Pin. 12.
D r i v e .
the engine is in operation, then the check valve will open.
This lets tank oil at outlet (3) flow to inlet (4) for
temporary operation of the steering pilot system.
If the engine should stop, the check valve opens to let oil
at outlet (3) go into inlet (4). This oil is used to operate the
steering pilot system when supplemental steering is part
of the steering system.