Back pressure valve

In a valve comprising

• a tubular body having a flow passageway therethrough providing an inlet at one end of the passageway and an outlet at the other end of the passageway,
• an annular seat about the passageway between said inlet and outlet, and providing a flow passage forming part of said passageway,
• a closure ball in said passageway on the outlet side of said seat adapted to engage said seat and block flow through said seat and movable in said passageway between a closed position engaging said seat and thereby blocking flow through said seat and an open position out of engagement with said seat leaving said seat open for flow therethrough,
• a helical spring in said passageway downstream from said ball and seat bearing at one end against said ball urging said ball into closed position, and
• support means in said passageway down stream from said spring and ball and seat and upstream from said outlet secured to said body and providing a support seating for the other end of said spring to take the the reaction force thereof,
• said support means including a footing comprising at least one strut connected to said seating and to said body leaving a flowpath past said seating having a cross-sectional area at least as large as that of the flow path through said seat passage,
• said spring having a smaller outer diameter than the minimum transverse inner dimention of said passageway leaving a flow path past the spring therearound having a cross-sectional area at least as large as that of said seat,
• the improvements wherein:
• said support means seating is a fixed imperforate cap closing said other end of said spring against fluid flow therethrough on its way to said outlet,
• said ball in the open position of the valve being in engagement with only said one end of the spring and providing means to guide flow outwardly of the spring, there being an annular flowpath extending axially from the equator of the ball to the spring and extending circumferentially all around the ball between the ball and said body, said annular flow path forming part of said passageway through the valve body,
• said annular flow path having at least as great a cross-sectional area as the flow path through said seat,
• said flow passage through the valve having, when the valve is open, a cross-sectional area that everywhere throughout its length is at least equal to that of said flowpath through said seat, exclusive of any area interiorly of the spring,
• whereby buckling of the spring will not prevent said passageway from having at all places a cross-sectional area at least equal to that of said flowpath through said seat when said valve is open,
• said footing comprising a slotted tube forming a plurality of struts extending axially away from said other end of said spring, the end of said tube farthest from said spring being exteriorly threaded forming a threaded pin, said body having a threaded box formed about said passageway, said threaded pin at one end of said tube being screwed into said box.