Patent ID: 7681650

Claim:
A downhole tool for attachment to a work string, the downhole tool having an inner wall disposed above a central longitudinal axis, the inner wall defining a central bore for passage of fluid from an upstream location to a downstream location; the downhole tool also having a valve seat, adapted for receiving a plug having a plugging dimension, for use in the central bore of the downhole tool, wherein the valve seat comprises: a substantially cylindrical body having a first bore therethrough defined by an inner surface of the body and the body being of a first volume; a first clearance through said body, defined by a portion of said inner surface, which is smaller than the plugging dimension; a seating surface located upon the inner surface facing upstream for sealingly engaging with said plug and substantially occluding passage of said fluid from said upstream location to said downstream location; wherein a pressure differential is developed across said valve seat when said plug sealingly engages said seating surface, applying force to said seating surface; said body being formed of an elastic material which compresses to a second volume, smaller than said first volume, by application of said force to provide a second clearance to said body which is greater than the plugging dimension, and thus allows passage of said plug downstream within said fluid conduit; and wherein after passage of said plug, said body returns to said first volume with substantially said first clearance; wherein the central bore of the downhole tool has an open upper end for receiving the plug, and wherein the tool is actuated and returned to its initial configuration by the passage of the plug through the valve seat.