Abstract: A system for varying specific gravity of a submersible or any immersed obt under a pressurized environment which includes a compressible piston designed to collapse a certain amount proportional to the submersible's depth so that the specific gravity of the submersible or other immersed object varies and remains almost equal to the specific gravity of the surrounding medium such as water.

Abstract: A pressure-balanced separation nut for releasably engaging a threaded elet. The separation nut includes nut segments which are housed within the cavity of a housing and are held in an assembled element-engaging condition by a slidable piston and a piston ring which surrounds the nut segments. A buffer piston bottoms within the slidable piston and has a conical face which slopes toward the axis and rests upon the inner ends of the nut segments. Fluid pressure is exerted on the inner face of the slidable piston to move it sufficiently in an axial direction to permit radial movement of the nut segments thereby quietly releasing the threaded element without the requirement of unthreading the threaded element. The conical face of the buffer piston forces the nut segments radially outward to aid in their separation from the threaded element.