Pressure reducing valve spool

Claim 1

In a pressure reducing valve for an expandable fluid having a valve housing defininG a valve chamber, said housing to be connected to a source of expandable fluid under high pressure for the transmission of said fluid at a reduced pressure to a valve outlet defined by said housing, a seat formed by said housing, a valve spool mounted for reciprocal movement in said housing between fully opened and closed positions, said spool having a mating annular seat sealing against the housing seat, movement of said spool away from said housing seat defining a gradually increasing entrance flow area for said fluid to be admitted to the interior of said housing, the improvement residing in that the valve chamber together with said valve spool defines three longitudinal sequentially related fluid flow zones, said first zone being an entrance zone beginning from said housing seat and extending for the distance of spool movement between fully opened and closed positions, said housing having the internal diameter Do of said housing seat at the beginning of the entrance zone, said valve spool converging evenly throughout said entrance zone toward the axis of said spool to have a diameter D1, the difference between diameters Do and D1 defining in combination with surrounding valve housing a maximum entrance cross-sectional flow area which can admit a maximum mass flow of fluid into said chamber; the second flow zone being defined by said spool and adjacent areas of said housing wherein said spool continues to converge smoothly toward its axis to a minimum valve spool diameter D2, the transverse cross sectional annular flow area at D2 being substantially equal to the minimum transverse cross sectional area of said valve outlet such that the converging surface of the spool together with said housing provides a continuous expansion of the fluid at a constantly decreasing rate of expansion but without over-expansion of said fluid; and a third flow zone is defined by said housing and said spool which diverges from its axis in an amount to re-direct the expanded fluid completely to fill the valve chamber adjacent to the diverging portion of the spool with a minimum of further expansion of fluid and optimum flow distribution to said valve outlet.