In a lower kelly valve positioned beneath the kelly of a drill string connected to surface drilling equipment and mounted between an internally threaded lower tubular member defining a downstream flow passage and an interfitting externally threaded upper tubular member defining an upstream flow passage; an improved ball valve structure comprising:Ball Valves an enlarged valve chamber formed in said lower tubular member and having an annular groove therein adjacent said valve chamber and extending about said downstream flow passage; a ball valve member mounted in said valve chamber for rotation between open and closed positions relative to said flow passage; an annular downstream seat mounted in said annular groove for sealing against said ball valve member; resilient means urging said downstream seat toward sealing engagement with said ball valve member; Ball Valvesan annular groove in said upper tubular member adjacent said valve chamber and extending about said upstream flow passage; an annular upstream seat mounted in said annular groove of said upper tubular member for sealing against said ball valve member; resilient means urging said upstream seat toward sealing engagement with said ball valve member;BALL VALVES said ball valve member having a generally spherical body with a central bore therethrough and a fluid equalizing opening extending in the closed position of said ball valve member from said central bore through said body to said upstream flow passage to provide fluid communication from the upstream flow passage to said valve chamber to permit equalizing the fluid pressure acting on said annular seats in said closed position from upstream fluid pressure thereby to provide equal seating forces between said ball valve member and said annular upstream and downstream seats for facilitating easy rotation of said ball valve member from said closed position to said open position, said fluid equalizing opening in the open position of said ball valve member being in direct fluid communication with said valve chamber whereby fluid pressure from said flow passages is transmitted to said valve chamber for equalizing the fluid pressure acting on said annular seats; and manual means connected to said ball valve member to rotate said ball valve member between open and closed positions.

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