Drill string dump valve

Claim 1

A drill string dump valve comprising a valve body formed with a through passageway for the passage of fluids therethrough from an upper end to a lower end when said valve is vertically disposed, said passageway comprising a downwardly expanding section, said body being formed with an opening communicating said section of said passageway with the outside of said body, means to releasably seal said opening at said sectioN against the flow of fluids therethrough, said section of said passageway comprising an upper smallest cross-sectional area and a lower largest cross-sectional area, said releasable sealing means comprising a valve member moveable within said passageway and adapted to close said opening, said valve member comprising an upper smallest cross-sectional area adapted to fit snugly within said upper smallest cross-sectional area of said section and a lower largest cross-sectional area which is a predetermined amount smaller than said lower largest cross-sectional area of said section, whereby said valve member may move freely down and away from said opening to open said opening for fluid flow, said releasable sealing means comprising an operating member adapted to pass down through the inside of the drill string to contact said moveable valve member, said passageway comprising a throat portion extending upwardly from said upper smallest crosssectional area thereof and adapted to guide said operating member into sealing relation with said valve member, said releasable sealing means comprising a plurality of shear bolts passing through the wall of said valve body and the wall of said valve member to hold said valve member in sealing relation with said opening, said bolts being formed with a bolt head portion positioned on the inside surface of said valve member, and means to form a fluid tight seal at the zone of contact between said bolt head and the inside surface of said valve member.