Patent ID: 8708051

Claim:
An isolation valve for use as part of a casing string, the isolation valve comprising: a housing having a bore and a valve cavity; a valve member movable between a first position in which the valve member obstructs the bore of the housing and a second position in which the valve member is disposed in the valve cavity, the valve member having a locked position in which the valve member is locked in the valve cavity; a flow tube configured to allow movement of the valve member between the first and second positions; a piston coupled to the flow tube; an engagement assembly attached to the housing by a shearable member, the piston configured to move the flow tube into engagement with the engagement assembly to substantially prevent debris from entering the valve cavity when the valve member is in the second position, and configured to move the flow tube out of engagement with the engagement assembly when the valve member is in the first position, wherein the engagement assembly is movable relative to the housing upon release of the shearable member when the valve member is in the locked position; and a compression spring disposed between the piston and the flow tube and configured to bias the flow tube into contact with the engagement assembly when the valve member is in the second position.