Scuba Diving Types Open Circuit With A Demand Regulator

· the Aqua-Lung - a system consisting of one or more cylinders containing a high pressure breathing gas connected to diving regulator that supplies the diver with as much of the gas as he needs at a pressure suitable for breathing at the depth of the diver. See diving cylinder for more information about the cylinders and how they are arranged.

1.1.2 Constant flow

These were open-circuit breathing sets without a regulator. They run out of air quicker than aqualungs. There were attempts at designing and using these before 1939, for diving and for industrial use, but not much came from them. Examples were "Ohgushi's Peerless Respirator", and Commandant le Prieur's breathing sets (see below under History).

1.1.3 "Twin-hose" open-circuit scuba

The early aqualungs had one or more (usually two) cylinders lengthwise on the back. The first and second stages of the regulator were in a large circular valve assembly mounted on top of the cylinder pack. It had two wide breathing tubes like on many modern rebreathers.

The return tube was not for rebreathing but because the air exhaust needed to be at the same depth as the regulator's second stage diaphragm to avoid pressure differences, which would cause a free-flow or resistance to breathing according to the diver's attitude in the water.

Scuba equipment at this period was not used with any sort of buoyancy aid such as a buoyancy compensator, but a plain strap harness like on a rucksack or spray-tank-pack. Many did not have a backpack plate, but the cylinders were directly against the diver's back.

1.1.4 "Single-hose" open-circuit scuba

Most modern open-circuit scuba sets have a diving regulator consisting of a first stage pressure reducing valve that is sealed over the diving cylinder’s output pillar valve, and the second stage “demand valve” at the mouthpiece, with a thin pressure hose linking the two stages. This type is called "single hose". Many modern scuba sets have a spare demand valve on its own hose, which is called an “octopus” or “alternate air source”.

There are several methods of mounting open-circuit scuba sets on the diver. Primary scuba sets generally mounted on the BC worn by the diver, such as a wing or "stab-jacket". Where an ABLJ-type BC is used, a separate backpack worn on the diver’s back and supported by straps from the shoulders is used.

Decompression “stage” cylinders are slung at the diver’s side or front from strong points on the buoyancy compensator harness.

1.1.5 Cryogenic open-circuit scuba

There have been designs for a cryogenic open-circuit scuba, which has liquid-air tanks instead of cylinders. One type is the Russian Kriolang, which was copied from Jordan Klein 's "Mako" cryogenic open-circuit diving set.

This link shows pictures of a Kriolang that was made in 1974. Its diving duration is likely several hours. It would have to be filled immediately before use.

1.2 Rebreathers

In these, the user breathes a breathing gas in and out of a breathing bag. The oxygen that he uses is replaced, nearly always from a cylinder. The carbon dioxide which he breathes out is emoved, nearly always in a canister full of absorbent. This type of SCUBA equipment is known as 'closed circuit'. Its economic use of gas allows dives of much longer endurance than is possible with open circuit equipment. See Rebreather for more information.

1.3 Alternatives to scuba

surface supplied diving - mainly used in professional diving for long or deep dives where an umbilical line connects the diver with the surface providing breathing gas, and sometimes warm water to heat the diving suit, and usually nowadays voice communications.
free-divingFree-diving is an aquatic sport, considered an extreme sport, in which divers attempt to reach great depths unassisted by breathing apparatus. The world record for the "No Limits" category of competitive free diving is held by French diver Loic Leferme. - swimming underwater on a single breath of air.
snorkeling - a form of free-diving where the diver's mouth and nose can remain underwater when breathing, because the diver is able to breathe at the surface through a short tube known as a snorkel.

2 Breathing sets used out of water

Independent breathing sets are also used on land (for example, in industry and mine rescue and fire services), and are then called SCBA = Self Contained Breathing Apparatus. Industrial rebreathers have been used since soon after 1900. Rebreather technology is also used in space suits

The first open-circuit industrial breathing sets were designed by modifying the design of the Cousteau aqualung.

3 History

The first known mention of air tanks is in Italy, 15th century: Leonardo da Vinci affirmed in his Atlantic Codex (Biblioteca Ambrosiana, Milan) that systems were used at that time to artificially breathe under water, but he did not explain them in detail due to what he described as "bad human nature", that would have taken advantage of this technique to sink ships and even commit murders. Some drawings, however, showed different kinds of snorkels and an air tank (to be carried on the breast) that presumably should have no external connections. Other drawings showed a complete immersion kit, with a plunger suit which included a sort of mask with a box for air. The project was so detailed that it included a urine collector, too.

In 1829 Charles and John Deane of Whitstable in Kent in England designed the first air-pumped diving helmet. It is said that the idea started from a crude emergency rig-up of a fireman's water-pump (used as an air pump) and a knight-in-armour helmet used to try to rescue horses from a burning stable.

After Leonardo's studies, and those of Halley the astronomer, in 1837 Augustus Siebe developed standard diving dress, a sort of surface supplied diving apparatus.

Some time afterwards, the Frenchman Joseph Cabirol started making standard diving dress.

In 1865 Benoit Rouquayrol and Auguste Denayrouze designed a diving set with a backpack spherical air tank that supplied air through the first known demand regulator. The diver still walked on the seabed and did not swim. This set was called an aérophore. But pressure cylinders made with the technology of the time could only hold 30 atmospheres, and the diver had to be surface supplied; the tank was for bailout. The durations of 6 to 8 hours on a tankful without external supply recorded for the Rouquayrol set in the book "Twenty Thousand Leagues under the Seas" by Jules Verne, are wildly exaggerated fiction. Judging by Jules Verne's inaccurate attempts in the book at describing how the Rouquayrol set worked, how the demand regulator works was not generally known or had already been forgotten when he wrote the book, which was published in 1870.

In the late 19th century and after, industry could make high-pressure air and gas cylinders. That prompted a few inventors down the years to design open-circuit compressed air breathing sets, but they were all constant-flow, and the demand regulator did not come back until 1939.

In 1879 Henry Fluess invented the first closed circuit breathing device using stored oxygen and adsorption of carbon dioxide by a caustic soda or rebreather for the rescue of mineworkers who were trapped by water.

In 1893 Louis Boutan invented the first underwater camera.

In 1908 John Haldane , Arthur Boycott , and Guybon Damant published "The Prevention of Compressed-Air Illness", detailed studies on the cause and symptoms of decompression thickness.

In 1912 Haldane, Boycott and Damant published the U.S. Navy tested tables.

In 1915 Sir Robert Davis invented an oxygen rebreather called the "Submarine Escape Apparatus" to escape from sunken submarines. It was the first rebreather to be made in quantity. After that, various sorts of industrial oxygen rebreathers were made down the years for use in unbreathable atmospheres on land.

In 1933 Yves Le Prieur invented a constant-flow open-circuit breathing set. It could allow a 20 minute stay at 7 meters and 15 minutes at 15 meters (these data appear however to be re-checked). These sets were used by the first known sport diving club, which started in 1935.

In the 1930's sport spearfishing became common in the Mediterranean, and spearfishers gradually developed the common sport diving mask and fins and snorkel, and Italian sport spearfishers started using oxygen rebreathers.

In 1939 the Frenchman Georges Commeinhes developed a two-cylinder open-circuit apparatus with demand regulator. The regulator was a big rectangular box between the cylinders. He offered this set to the French Navy, which could not continue developing uses for it because of WWII. In July 1943 he reached 53 meters (about 174 feet) using it off the coast of Marseille, But he died in 1944 in the liberation of Strasbourg in Alsace.

In 1941, during WWII, Italy used rebreathers were used for one of the best known and most spectacular war actions: Italian "Decima Mas" (elite navy corps at the orders of commander Junio Valerio Borghese) entered at nighttime the port of Alexandria in Egypt underwater. They used special underwater vehicles ("maiali" = pigs) and breathing apparatus, and were able to silently attach mines on the bottoms of the ships, that later were effectively sunk.

In 1943 Jacques Cousteau and Emile Gagnan invented an open-circuit diving breathing set, using a demand regulator which Gagnan modified from a demand regulator used to let a petrol-driven car run on a big bag of coal-gas carried on its roof during wartime shortages of petrol. This set was later named the Aqua-Lung. This word is correctly a tradename that goes with the Cousteau-Gagnan patent, but in Britain it has been commonly used as a generic and spelt "aqualung" since at least the 1950's, including in the BSAC's publications and training manuals, and describing scuba diving as "aqualunging". In October 1944 Frédéric Dumas reached 62 meters (about 200 feet) with this set.

In 1953 the National Geographical Society Magazine published an article about Cousteau's underwater archaeology at Grand Congloué island near Marseilles, and in French-speaking countries a diving film called Épaves (= Shipwrecks) came out. That started a massive public demand for aqualungs and diving gear, and in France and America the diving gear makers started making them as fast as they could. But in Britain Siebe Gorman Ltd kept aqualungs expensive, and many British sport divers had to use home-made breathing sets and ex-armed forces or ex-industry rebreathers, and some became expert at home-making diving demand regulators from industrial parts. Finally Submarine Products Ltd in Hexham in Northumberland in England designed round the Cousteau-Gagnan patent and made sport diving breathing sets accessibly cheap.

In those times, free-swimming diving suits were not readily available to the general public, and as a result many scuba divers dived in merely swimming trunks. That is why scuba diving used often to be called "skindiving".

In 1958 the television series Sea Hunt introduced SCUBA diving to the television audience.

In Italy, sport diving oxygen rebreathers continued to be made well into the 1960's.

Films have also popularized the sport. SCUBA diving is featured in films such as The Abyss (including as-yet-fictional deep-sea liquid-breathing sets), James Bond in Thunderball (using both sorts of open-circuit scuba) and Fantastic Voyage (using rebreathers).

4 Related topics

5 External links

Divers Alert Network
Brief history of diving - From antiquity to the present.
Top Scuba Sites - Scuba sites as ranked by user popularity.
Scuba Monster - Scuba Usenet discussions and archive.

Acronyms Diving

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1 Types

1.1 Open circuit

1.1.1 With a demand regulator