Systems of expansible well tools

Claim 1

A WELL TOOL ADAPTED FOR INCLUSION IN A TUBING STRING OF A WELL COMPRISING TWO COAXIALLY ALIGNED TELESCOPING PARTS CONNECTIBLE TO SEPARATE ADJACENT SECTIONS OF A TUBING STRING; RADIALLY EXPANSIBLE MEANS DISPOSED TO BE EXPANDED INTO POSITION ENGAGING A WELL CASING UPON MOVEMENT OF ONE OF SAID TELESCOPING PARTS TOWARD TELESCOPICALLY COLLAPSED POSITION RELATIVE TO THE OTHER OF SAID PARTS; A RELEASABLE MEANS INCLUDING A SEALED CHAMBER BETWEEN OPPOSED SHOULDERS ON SAID PARTS, A FLUID IN SAID CHAMBER UNDER PRESSURE SUFFICIENT TO RETAIN SAID PARTS IN TELESCOPICALLY EXPANDED POSITION, AND A MEANS FOR RELEASING THE FLUID FROM THE CHAMBER, FREEING THE PARTS TO MOVE INTO TELESCOPICALLY COLLAPSED POSITION EXPANDING THE EXPANSIBLE MEANS.