How does aqualungs work?

Answer 1

An aqualung is comprised of two parts - the tank, and then regulator.

The tank simply contains highly compressed gas. The regulator reduces the pressure of that gas to a level which is breathable by the diver for a particular depth.

In a normal Aluminium diving cylinder, the breathing gas (usually plain air) will be compressed to about 3,000 PSI (200 bar).

The regulator has two stages, the first stage (the bit that gets attached to the tank), and the second stage (the bit that the diver puts in her mouth). The first stage will reduce the air pressure coming from the tank from 3,000 PSI down to about 300 PSI (20 bar). This air then flows down the hose to the second stage. The second stage then reduces the pressure from 300 PSI to the ambient pressure at the diver's depth (the deeper a diver goes, the greater the ambient pressure). Accordingly, no matter how deep a diver goes, the air will be delivered as pressure which enables her to breathe normally despite the water pressure on her body.

The regulator works by way of a demand valve. When the diver inhales, that lowers the pressure in the second stage housing. This opens the demand valve, and higher pressure air flows in from system. Once the air pressure in the house is restored to equilibrium, the demand valve closes.

If the regulator starts to malfunction, it can either deliver air at too low a pressure (so it will become hard to breathe) or too high a pressure (the regulator will "free flow" with bubble coming out).