Pioneer Natural Resources USA, Inc.

Theodore Lee Cottrell

Ann Kamel Fitzgerald

Michael Gay

Phillip Graham Knight

Michael Glenn Gay

A valve for limiting differential pressure applied to a downhole tool includes a housing and a movable piston/mandrel assembly therein. In a closed position, drilling mud or other fluid may be communicated through a central bore of the valve to the tool. When the differential pressure between the central bore and the wellbore exceeds a first predetermined value, the piston/mandrel assembly moves from a first position obstructing one or more relief ports to a second position not obstructing them, thereby providing a fluid path from the central bore of the valve to the wellbore bypassing the tool and relieving the differential pressure thereacross. When the differential pressure decreases to less than another preselected value, the piston/mandrel assembly returns to its original position again obstructing the relief ports. A trigger mechanism is provided to allow more precise control and separation of the preselected differential pressure values.

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Keller, TX, United States of America

Theodore Lee Cottrell