How Air Lift Bags Work

Flexible buoyancy works by displacing water inside a flexible container with a pressure slightly exceeding the surrounding water. This creates a 'hole in the water' with a buoyancy equal to the volume of water displaced.

Because the volume is created by overpressure, if the surrounding pressure increases, the internal volume will decrease and buoyancy be reduced.  So, assuming no more air is pumped in, the volume of flexible buoyancy will decrease as it goes deeper because the air inside becomes compressed and occupies a smaller volume.

Conversely, as it rises, the air inside will experience a lesser surrounding pressure and so expand to provide an increasing volume as it rises.

Simply - a lift bag going down is compressed and provides decreasing buoyancy while a bag coming up expands and provides increasing buoyancy.

 

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