A mud saver valve for preventing drilling mud from escaping from a kelly when a drill string is broken below the kelly, said valve comprising:
- a tubular valve body having first and second ends, said first end being provided with means for attachment in fluid communicating relationship with the kelly, said second end being provided with means for attachment to said drill string;
- an annular seat fixed in the interior of said valve body adjacent its first end;
- a tubular closure member within said valve body, said closure member being provided with a selectively closed seating end for seating in valve closing engagement with said annular seat, an open non-seating end in fluid communicating relationship with said drill string, and an annular expansion in the outer diameter of said closure member adjacent said seating end;
- a top and bottom spacer ring disposed in sliding relationship around said tubular closure member intermediate said annular expansion and said non-seating end of said closure member, said spacer ring and annular expansion cooperatively defining an annular chamber around said closure member;
- a helical spring disposed around said closure member within said chamber for biasing said closure member towards said annular seat;
- an annular retainer between said top and bottom rings, said retainer being carried by said valve body for preventing longitudinal displacement of said bottom spacer ring towards said annular expansion and preventing downhole pressure from being communicated to said helical spring;
- a first, annular, unidirectional seal disposed in substantially sealing engagement between said annular expansion and the interior annular wall of said tubular valve body for permitting fluid to pass out of said chamber but not into said chamber, said first unidirectional seal being maintained in a stationary position relative to said closure member by means embedded in said valve body, and said annular expansion of said closure member extending a sufficient length of said closure member to maintain said first unidirectional seal and said annular expansion in substantially sealing relationship as said closure member moves between a seating position and a non-seating position with said annular seat;
- a second, annular, unidirectional seal disposed around said closure member adjacent said non-seating end of said closure member between said bottom spacer ring and said non-seating end of said closure member and in substantially sealing engagement between the exterior of said closure member and the interior annular wall of said tubular valve body for permitting fluid to pass out of said chamber but not into said chamber, said second unidirectional seal being stationery relative to said closure member,
- said inner diameter of said valve body being reduced between said second unidirectional seal and said second end of said valve body thereby forming a reduced diameter portion, said reduced diameter portion providing a shoulder on which said second unidirectional seal rests, said second unidirectional seal being disposed around said closure member adjacent said bottom spacer ring but outside said chamber, said helical spring resting on said top spacer ring;
- an opening in said closure member between said annular expansion and said seating end through which fluid may pass to the interior of said closure member when said valve opens, against the bias of said helical spring;
- and
- means for selectively opening said seating end of said closure member in response to downhole pressure to vent said downhole pressure past said valve, said means for selectively opening said sealing and comprising a substantially circular plate with an upwardly extending spear pointing in the direction of said first end of said valve body, said plate further having a plurality of depending, deformable legs for insertion into the seating end of said closure member, said deformable legs having enlarged ends for retaining said plate in axially sliding relationship with respect to said closure member, said plate being movable between a first position wherein said plate substantially sealingly closes said seating end of said closure member and a second position wherein said seating end is open, the area between said legs defining pressure release openings through which downhole pressure is vented to the surface,
- an annular face of said annular seat against which said closure member seats being beveled, and an annular face of said seating end of said closure member which seats against said annular seat being cooperatively beveled so that said faces seat along an annular inclined surface, and wherein the annular bottom edge of the circular plate is inclined inwardly and downwardly, and the annular surface of the closure member against which the annular bottom edge of the closure plate seats is correspondingly inclined to provide an inclined sealing surface along which the circular plate and closure member seal.