Вот нашел.

Loader Valve - Variable Flow
Priority Inlet Section Operation
Service Selected (no steering demand)
If the steering is not selected, there will be no pressure
demand signal in chamber C. Pump pressure is ‘dead
ended’ at the steer unit, this pressure is felt in chamber F via
priority port PR and drilling G. The pressure is sufficient to
force spool E down against the force of spring D. The
position of the spool now allows oil from the pump inlet port
P to flow into passage H and on to the selected service via
the valve block service ports.