Ever since the 19th century, scientists had tried to invent an effective self-contained breathing device for divers. But if their inventions worked at all, they involved cumbersome diving suits or restricting safety lines. Then in 1943 a French naval captain, Jacques-Yues Cousteau, and his colleague Emile Gagnan, invented the aqualung. Cousteau used the invention to dive to depths of 200ft (60m).
A person’s lungs are not powerful enough to expand against the pressure of water below about 18in (450mm). Water pressure increases rapidly with depth, and at 33ft (10m) it exerts a pressure equal to 2 atmospheres – nearly 30lb per square inch (2 kilos per square centimetre).
To breathe underwater, a diver has to receive air at the same pressure as the surrounding water. This is what the aqualung – or scuba (self-contained underwater breathing apparatus) – provides. Air is stored at high pressure – up to 3000lb per square inch (200 atmospheres) – in cylinders on the diver’s back with a tube to a mouthpiece.
At reaches the diver through a two-stage regulator. The first stage reduces the pressure to about 150lb per square inch (10 atmospheres) above the surrounding water.
The second stage, in the mouthpiece, supplies the diver with air at the same pressure as the surrounding water. A flexible diaphragm in the mouthpiece is open to the water on one side and to an air chamber on the other side. As the diver inhales, the diaphragm is drawn inwards and presses against a lever in the chamber. This opens a valve to let in air from the tube, which drops in pressure as it enters.
When the diver finishes inhaling, the air coming into the chamber pushes against the diaphragm, shutting the valve and cutting off the airflow.
Even when the diver is not inhaling, an increase in water pressure as he dives pushes the diaphragm forward to open the valve and let in air from the tube. So the air in the mouthpiece chamber is always at the same pressure as the surrounding water.
Picture Credit : Google