| 摘要 |
A tubular valving system includes, a tubular, a seat, a sleeve movably engaged with the seat between at least a first position, a second position and a third position, a release member between the sleeve and the seat that maintains the sleeve relative to the seat in the first position until release thereof, a biasing member configured to urge the sleeve from the second position toward the third position, and a flapper sealingly engagable with the seat. A first threshold pressure against the seated flapper causes release of the release member allowing the sleeve and the seat to attain the second position. A subsequently drop in pressure against the seated flapper below a second threshold level allows the biasing member to move the sleeve relative to the seat to the third position thereby unseating the flapper from the seat and preventing the flapper from again seating with the seat.
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