Variable diameter drill rod stabilizer

Claim 1

A variable diameter drill rod stabilizer for use in a drilling operation comprising: (a) an outer housing adapted to attach to and become a part of a drill rod string; (b) a piston within said housing, said piston having a flow passage therethrough, a flow passage outlet, and being capable of limited axial movement within said housing; (c) a plurality of cam members including cam surface means axially positioned along said piston; (d) a plurality of borehole wall engaging members contained in said housing and including cam follower surfaces associated with said cam surface means whereby said wall engaging members move from a contracted position to an expanded position beyond the outer surface of said housing in response to axial movement of said piston; (e) bias means adapted to prevent forward movement of said piston within said housing in response to a first lower pressure drop of fluid flowing through said flow passage and to allow forward movement of said piston within said housing in response to a second higher pressure drop of fluid flowing through said flow passage; and (f) a piston stop member including longitudinal flow passage means therethrough, said stop member being downstream from the outlet of the flow passage through said piston when said stabilizer is in the contracted position and upstream from said stop member when said stabilizer is in the expanded position.