Submerging with an aqualung

The pioneer of diving, Jacques Cousteau, and engineer Emile Gagnan developed the first regulator in 1940s. The world-known Mistral regulator, which is still popular with historical diving enthusiasts, was developed a few years later.

Mistralin nimilaattoja on painettu neljällä eri osoitteella valmistusosoitteesta riippuen.
Mistral brand badges exist with four different addresses depending on where they were manufactured.

Text and photographs: Pekka Lahtinen
Translation by Ralf Strandell

A child has never opened a christmas present more excited than we were while unwrapping our first ‘aqualung’. If it would function, it would revolutionize diving.” — Jacques Cousteau writes in his book Silent world, that he has just fetched, in june 1943, a wooden box from the railway station containing a breathing apparatus working on compressed air. He hurried to the sea shore with his friends Philippe Tailliez and Frederic Dumas in order to test this apparatus.

Cousteau had earlier tested an open circuit breathing apparatus designed in 1933 by the French naval officer Yves Le Prieur. It featured a full face mask and a breast mounted bottle. The constant frow of air to the mask was adjusted by the valve on the bottle. This apparaturs was not convenient however, and the constant flow quickly exhausted the air supply. Cousteau also experimented with other breathing apparatus. The apparatus developed by Maurice Fernez relied on surface supplied air as it featured an air pump on a boat. Air was delivered to the divers mouth piece. Breaking air hoses caused life-threatening situations however. Oxygen apparatuses were not safer either. Cousteau nearly lost hist life while diving too deep breathing oxygen.

The first “aqualung”

Jacques Cousteau donned the breathing apparatus sent in a wooden box. It comprised a regulator, carrying straps and three cylinders of compressed air. He submerged at French Riviera and that dive marked the fulfillment of a dream, and something that he had tried to archieve for years. The regulator developed together by him and engineer Emile Gagnan, was operating flawlessly. They had thus invented an “aqualung”, a device that allowed a diver to breathe the air he carried, and which delivered air only on demand. A revolution in the development of diving apparatus was a fact.

Cousteau and Gagnan were granted a patent for their invention in 1945. The first commercially sold regulator, CG45, was manufactured the next year. It was sold from 1946 to 1955 by the company Spirotechnique SARL, that was renamed La Spirotechnique in 1951 . CG45 had a traditional corrugated hose design with fresh air delivery from the right hand side hose to the mouth piece and exhalation hose to the left. The exhaled air was further led to the regulator behind the divers neck and let out to water through holes in the regulator casing. The two stage CG45 was not a perfect regulator however. It was said that it requires breathing effort and that it is difficult to tune.

Mistral and the venturi-effect

In 1955 La Spirotechnique introduced a revolutionary new design: The Mistral regulator designed by Emile Gagnan. It got its name after the Mistral winds blowing over the Mediterranean. It was a single stage regulator with yoke attachment and it was easy to manufacture and service and it operated reliably. It was also lighter to breathe because of the new venturi nozzle, that Gagnan had deviced.

Mistral –61 with an Aqua-Stop mouth piece.

The Italian physicist Giovanni Battista Venturi discovered the Venturi effect at the end of the 18th century. The Venturi effect makes the flow of liquids and gases more efficient and in regulators it had a revolutionizing effect on comfort of breathing. The effect generates a kind of underpressure that increases the suction on the diaphragm in the regulator during inhalation. Air flows into the lungs almost by itself. Nowadays most regulators feature a Venturi nozzle, either a fixed or an adjustable one. The Venturi effect can be seen when a regulator is lowered into water with the mouth piece pointing upward: the regulator starts to free-flow. The Venturi effect is also put in use in carburetors of cars and in the nozzles of spray bottles.

Mistral was manufactured until 1976 and it was decorated by one of four different name plates depending on the manufacturing plant it was built in. The 1961 model featured a special “voice membrane” in its mouthpiece. It was thought that it would allow divers to speak. Unfortunately, it did not work. The mouth piece also had a bad shape and did not properly fit in the mouth. Next year it was replaced with the Aqua Stop mouth piece, that featured one-way valves to keep water out of the corrugated hoses.

Royal Mistral

In 1963 La Spirotechnique introduced the Royal Mistral regulator. Its pressure regulator got a rounder shape and it came equipped with an Aqua Stop mouth piece. The name plate no longer announced the manufacturing plant but had a crown instead to show distinction and royal value. Many consider Royal Mistral as the best ever corrugated hose regulator. Since 1965 it had an optional output for a submersible pressure gauge, too.

Royal Mistral in the mid 1970’s.
Many consider Royal Mistral as the best ever corrugated hose regulator. Pay attention to the strap on the mouth piece.

The Royal Mistral was replaced in 1980 by a second generation model sometimes known as “Black Label” (due to the colour on the name plate). The names of Cousteau and Gagnan were gone from the plate and the regulator featured an output for an submersible pressure gauge by default. Production was ceased in 1985 however, as the new one-hose design regulators proved to be more economical and more reliable. Production license of Royal Mistral was sold to the French company Beuchat, that continued production a few years under the name “Espadon Tarzan”.

Changes took place under the years and La Spirotechniqe was renamed Aqua Lung International. In 2005 Aqua Lung introduced a batch of new corrugated hose Aqua Lung Mistral regulators to commemorate the old Mistral. It was a new design, a two-stage Mistral featuring all modern outputs. At a price point of 900 dollars it was expensive and it was only sold for two years.

Diving position affects air delivery

A divers orientation in water greatly affects the breathing effort while using double hose regulators. Breathing is very light when the diver stays in an upright position in water. If the diver is on his back, air is flowing by itself. However, when diving horizontally with bottles above the back, breathing (inhaling) is more difficult than it is with modern one hose regulators. Exhaling is a bit heavier also, as the air must travel through the hose to the output behind the neck.

The lack of outputs or them being limited to a single submersible pressure gauge output was standard in 1950’s and in 1960’s. Cylinders featured a reserve gas lever that shut the valve when only 30 bar was left. This was considered sufficient notification in those times as the diver could then pull the reserve gas lever to free the remaining air and resurface. Buoyancy compensating vests (BCD’s) only became common in the 70’s and the early models featured a small bottle of compressed air. Hence, there was no need for an output in the regulator either. Nowadays this problem can be circumvented by getting a cylinder valve with two outputs (Y- or H-valve). One output would host a Mistral and the other one would host a modern first stage serving modern pieces of kit (BCD, SPG, Octo).

The cylinder valve by La Spirotechnique features a reserve gas lever that shuts the valve when only 30 bar is left..
Notice the lever on the right.

After a dive a regulator needs to be properly washed in sweet water to remove residual salt. In addition, a small amount of water can enter the exhalation hose through the Aqua Stop mouth piece and great care must be taken to fully remove this water. If the regulator is to remain unused for a longer period of time, the inhalation diaphragm separating the dry chamber from the wet chamber must be treated with talcum powder. Any grease must absolutely not be used. Also the exhalation valve, the “duckbill”, in the wet chamber requires talcum powder. The duckbill is a flat rubber thing than lets air escape while preventing the entry of water into the exhalation hose.

A sizeable inhalation diaphragm separates the dry chamber from the wet chamber. The wet chamber contains the exhalation vent, the “duckbill” visible in the picture.

Historical diving gains popularity

In Finland the Mistral and other corrugated hose (double hose) regulators were used in the 1950’s and in the early 1960’s. Swedish single hose regulators soon overtook the market however. Especially the brands Cyklon and Airmatic gained a lot of popularity and double hose regulators fell out of use. World-wide La Spirotechnique started to increasingly design and sell single hose regulators. The old models would have been lost to the history had not historical diving gained popularity. Nowadays some underwater videographers favor double hose regulators as the exhalation bubbles will not interfere with videography.

Minimalistic historical setup.

In Europe and especially in the United States of America there are companies that specialize in collecting, refurbishing and selling historical diving equipment. Old regulators are refurbished and chrome-plated and spare parts, such as inhalation diaphragms and exhalation valves and name plates, are manufactured to the most popular models. Collectors in the United States of America are mostly interested in corrugated hose regulators sold by U.S. Divers. In Europe, old models by La Spirotechnique are more popular. Old diving equipment is not worthless. A properly refurbished and chrome-plated CG45 might cost up to 2000 euro! Retro diving has come to stay.

Further information

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