Importance

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Abstract

A downhole cut-off valve used for cementing a casing string, comprising: an outer hollow body, having a top end connected at the lower end of the casing string, an inner hole, an inner surface and a projecting shoulder forming on the inner surface and extending inwardly; an inner hollow body, arranged slidably in said outer hollow body and having an inner hole, a wall with a plurality of through holes and a projection forming on the wall and below the through holes and extending outwardly, the projection being adapted to fit with the projecting shoulder of said outer body to define a preliminary position of said inner body with respect to said outer body; the longitudinal positions of the through holes and the projection being arranged in such a manner that the projecting shoulder of said outer body is located therebetween when said inner body is placed in said outer body and will at least partially cover the through holes in response to the movement of said inner body; a relief member, blocking the upper end of the inner hole of said inner hollow body and releasing automatically to expose the upper end of the inner hollow body when necessary; an adjusting member, arranged in the lower portion of said outer hollow body and being able to move longitudinally, and; a resilient member, arranged between said outer hollow body and said inner hollow body and having one end against the projection of said inner body and another end against said adjusting member.

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First Claim