It is useful to understand how conventional scuba works. Nearly all diving apparatus presently available to the public falls into a class known asopen-circuit scuba.
This type of system was first introduced to recreational divers by Jacques Cousteau and Emile Gagnan, and employs a compressed gas supply and a demand regulator from which the diver breathes.
The exhaust gas is discarded in the form of bubbles with each breath, hence the term "open-circuit".
Open-circuit scuba is inherently inefficient: because only a small fraction of each inhaled breath is actually used by the diver for metabolism, there is a tremendous waste of useable oxygen (O2) with each breath.
Furthermore, the quantity of O2 lost in this manner increases with increasing depth.
Regulators are used to reduce the air pressure from in air in the scuba tank so that you are able to breathe the air. A scuba regulator is made of two parts. The first part takes the air from the cylinder and lowers the pressure. The second part delivers the air to your mouth – also called a First and second stage. The second stage is also knows as a “demand valve” or “DV” as it supplies air on demand only.
Jacques Cousteau & Emile Gagnan
Emile Gagnan and Jacques Cousteau invented the modern demand regulator in 1942. They redesigned a car regulator and invented a demand regulator that would automatically supply fresh air when a diver breathed. A year later in 1943, Cousteau and Gagnan began selling the Aqua-Lung - the original name for the first open-circuit scuba diving equipment. Before that, there were a few attempts at constant-flow compressed-air breathing sets. The original "Aqua-Lung" was an "open-circuit" design, so called because gas flows from the cylinder, to the diver, out into the water. Other scuba gear, invented earlier than the "Aqua-Lung", are now termed "closed circuit" or "Rebreather", as gas flows from the cylinder, to the diver, through a scrubber (which removes carbon dioxide), back to a secondary bag, and back to the diver again, in a relatively closed loop; this design is commonly called a Rebreather.
The word “SCUBA" (Self Contained Underwater Breathing Apparatus) originated in the United States Navy, (where it meant a frogman's Rebreather) and became the generic term for that type of open-circuit breathing set, and soon the acronym SCUBA became a noun — "scuba" – meaning to dive..
Jacques Cousteau was born on 11 June 1910, in Saint-André-de-Cubzac, Gironde, to Daniel and Élisabeth Cousteau. He discovered the sea in the creeks close to Marseille, France where his family settled. He completed his preparatory studies at the prestigious Collège Stanislas in Paris. In 1930 he entered the Ecole Navale and became an officer gunner. InToulon, where he was serving on the Condorcet, Cousteau carried out his first underwater experiments, thanks to his friend Philippe Tailliez.
In 1936, Tailliez lent him some Fernez underwater goggles, predecessors of modern diving masks. In 1930 he entered the French Navy as the head of the underwater research group. He later worked his way up the ranks as he became more famous and more useful to the navy. On 12 July 1937 he married Simone Melchior, with whom he had two sons, Jean-Michel (1938) and Philippe (1940). His sons took part in the adventure of the Calypso. Cousteau died at the age of 87 of a heart attack while recovering from a respiratory illness. He is buried in the Cousteau family plot at Saint-André-de-Cubzac Cemetery,Saint-André-de-Cubzac, France.
The years of the Second World War were decisive for the history of diving. After the armistice of 1940, the family of Simone and Jacques-Yves Cousteau took refuge in Megève, where he became a friend of the Ichac family who also lived there. Jacques-Yves Cousteau and Marcel Ichac shared the same will to reveal to general public unknown and inaccessible places: for Cousteau the underwater world and for Ichac the high mountains. The two neighbors took the first ex-aequo prize of the Congress of Documentary Film in 1943, for the first French underwater film: Par dix-huit mètres de fond (18 meters deep), made without breathing apparatus the previous year in Embiez (Var) with Philippe Tailliez and Frederic Dumas, without forgetting the paramount part played, as originator of the depth-pressure-proof camera case, by the mechanical engineer Leon Vèche (engineer of Arts and Métiers and the Naval College).
In 1943, they made the film Epaves (Shipwrecks): for this occasion, they used the aqua-lung, which continued the line of some inventions of the 19th century (Rouquayrol and Denayrouze's Aerophore) and of the early 20th century (Le Prieur). When making Epaves, Cousteau could not find the necessary blank reels of movie film, but had to buy hundreds of small still camera film reels the same width, intended for a make of child's camera, and cemented them together to make long reels.
During the 1940s Cousteau is credited with improving the aqua-lung design which gave birth to the open-circuit scuba technology used today. According to his first book, The Silent World: A Story of Undersea Discovery and Adventure (1953), Cousteau started snorkel diving with a mask, snorkel, and fins with Frédéric Dumas and Philippe Tailliez. In 1943, he tried out the first prototype aqua-lung which made lengthy underwater exploration possible for the first time
Émile Gagnan (November 1900 – 1979) was a French engineer and co-inventor of the demand-valve used for the first Scuba equipment ("Aqua-Lung") in 1943. The demand-valve, or regulator, was designed for regulating gas in gas-generator engines, but was found to be excellent for regulating air-supply under varied pressure conditions.
Gagnan was born in the French province of Burgundy in November 1900, and graduated from technical school in the early 1920s. He was employed as an engineer specializing in high-pressure pneumatic design by the large gas-supply firm Air Liquide. The first production ‘Scaphandre Autonome’ - or ‘Aqualung’ was released in France in 1946 under the identification code "CG45" ("C" for Cousteau, "G" for Gagnan and "45" for 1945, year of the patent). A year later, in 1947, Émile Gagnan and his family emigrated to Montreal, Canadaand he transferred to the employ of Canadian Liquid Air Ltd. There he set up a lab and proceeded to engineer, design, and prototype an incredible number of SCUBA and undersea technology ‘firsts’, including the direct ancestors of virtually every type of Scuba regulator in common use today.