Diving Bell - Mechanics

Mechanics

Diving bells are used as underwater search vessels and by working divers doing underwater work and salvage. The bell is lowered into the water by cables from a crane attached to a ship or dock. The bell is ballasted so as to remain upright in the water and to be negatively buoyant so that it sinks even when full of air.

Hoses, fed by pumps on the surface, provide compressed breathing gas to the bell, serving two functions:

• Fresh gas is available for breathing by the occupants, and excess gas leaks out under the lip of the wet bell, where it bubbles naturally to the surface.
• As a wet bell is lowered, increasing pressure from the water compresses the gas in the bell. If the gas pressure inside the bell were not raised by adding gas to compensate for the outside water pressure, the bell would partially fill with water as the gas was compressed. Adding pressurized gas ensures that the air space within the bell remains at constant volume as the bell descends in the water, as well as refreshing the air, which would become saturated with a toxic level of carbon dioxide and depleted of oxygen by the respiration of the occupants.

A similar principle to that of the wet bell is used in the diving helmet of standard diving dress, where compressed air is provided to a helmet carried on the diver's shoulders. Additional weights are carried on the waist and feet to prevent overturning. The modern equivalent of this diving equipment is used in surface supplied diving.

A wet sub may also provide a dry viewing chamber for the operator's head, acting as would a diving helmet.

The physics of the diving bell applies also to an underwater habitat equipped with a moon pool, which is like a diving bell enlarged to the size of a room or two, and with the water–air interface at the bottom confined to a section rather than forming the entire bottom of the structure.