Fluid pressure spool valve and method of controlling pressure forces acting thereon

摘要

The velocity head created at an inlet port of a spool valve decreases the static pressure head at the inlet. The valve is so constructed that the decrease in static pressure can act on only a very small effective area of the land side surface, with a substantial majority of the land side surface effective area being so positioned that it is not subject to the velocity pressure head and its lesser static pressure head. Therefore the majority of the effective land side wall area is not exposed to the decrease static pressure head, but is exposed primarily to the full static pressure head with virtually no velocity pressure head, as the opposite land. This therefore decreases the force differential tending to urge the spool valve toward the closed position and therefore decreases the amount of force which must be overcome to move the spool valve in an opening direction. As a near balance of static pressures acting in opposite directions on the spool valve lands is obtained, there is less resistance to the valve apply force. This is accomplished by providing recessed land facing surfacing areas in one or both of the lands of a typical two-land spool valve.