Mechanism for achieving the radial expansion of an annular elastomeric pack-off unit between the bore of a casing and the exterior of a liner, comprises a tubular sealing assembly threadably connected between the liner and the hanger and defining two inwardly projecting annular seals, an annular fluid...http://www.google.com/patents/US4479544?utm_source=gb-gplus-sharePatent US4479544 - Pressure actuated pack-off and method
