Piston ring system

Claim 1

A seal ring assembly having a pair of non-deformable rings disposed in an axial abutting relation and received in a peripheral groove having a bottom and side walls formed in a reciprocating member, said non-deformable rings having adjacent inner recesses defining a composite groove, outer bearing surfaces engageable with a surface to be sealed and inner surfaces slightly spaced from said bottom wall of said groove formed in said reciprocating member to define clearances therebetween, an expander ring of pressure deformable material comprising an annular body having smooth and continuous outer surfaces, said expander ring being received in said composite groove and having an inner surface adapted to engage said bottom wall of said groove in said reciprocating member, characterized in that the axial length of said inner surface on each of said non-deformable rings is of substantially knife edge thickness limiting the axial extent of said clearance available for displacement of portions of said expander ring within its elastic limits to prevent permanent distortion thereof, and said inner recesses of said non-deformable rings each being provided with a notch in the wall surface thereof adjacent to said expander ring for receiving a portion of said expander ring forced into said notch during expansion of said expander ring to form an interlock for preventing relative rotation between said rings.