1. Field of the Invention
This invention relates generally to a totally self-contained hermetically sealed, immersible device capable of assuming alternately, a non-buoyant and buoyant mode and particularly to a dual buoyancy device which, in its minimum volumetric dimension displaces a volume of liquid whose weight is less than that of the device thus causing it to sink; with an increase to maximum volumetric dimension but with unchanged total weight, the device then displaces a volume of liquid whose weight is greater than that of the device, causing it to rise and float in the liquid.
2. Prior Art
Buoyant devices suitable for attachment to various objects to cause them to be lifted to the surface of a liquid are well known. They are usually made of buoyant material or have a shell-like structure which makes them buoyant.
Under most circumstances, buoyancy of these devices is reduced so that they will sink, and they may be attached to an object. This is usually accomplished by admitting to the interior of the device, sufficient of the liquid in which the device is immersed so that its buoyancy is reduced and it sinks. After attachment to an object, liquid within the device is pumped or otherwise removed restoring its normal buoyancy; which resulting force lifts the attached object to the surface.