1930 - 1965 Rene Piel / Denayrouze 3 bolt helmet

The photographs below show a 12-bolt helmet made by Rene Piel. It is a relatively recent helmet as evident by the telephone, which is no longer ‘acoustic’ but ‘electric’ instead.

1930 - 1965 Rene Piel / Denayrouze 12 bolt helmet

Above: a Piel 3-bolt helmet. This helmet was built between 1930 to 1940 or after 1945. This is because the company badges were made of aluminum during WW2 and this one has a brass badge. The telephone connection on this helmet is an early electric one and the telephone is not an acoustic version. Photographs, David L.Dekker

1957. Rene Piel / Denayrouze 3-bolt helmet, ‘Marine Nationale’ ( navy )

The above drawing was produced in 1957 by the ‘technical service’ of the French navy in order to register the helmet as the standard diving apparatus for naval use. It is part of a set of genuine drawings which I bought several years ago. I am currently looking for a printer who can reprint it as a poster on heavy paper as it would make a high quality reproduction, quite suitable for framing. When they are available for sale I will announce it in the ‘For Sale and Wanted’ chapter.

Helmet collection www.pieds-lourds.com Photo’s David L.Dekker

Above: a Piel 3 bolt helmet. This helmet was built either between 1957 and 1965 for the french navy. The telephone connection on this helmet is the last version of the electric one, it has no acoustic telephone. Photo’s David L.Dekker

Whoever handles one of these helmets in their hands can hardly believe that it was meant to be used for underwater exploration because a motorcycle helmet is heavier built than the ‘Piel EP’... But a second look reveals that Piel, originally Denayrouze, turned back to its roots with this helmet. Their very first helmet diving apparatus also was a helmet with a demand valve: the pig snout mask or 3 bolt diving helmet with the regulator back pack. This little plastic helmet was designed by Yves Le Masson according to exactly the same idea, only has the size of the heavy brass and copper helmet been reduced to a light plastic shell with a rubber hood and neck seal inside of it. The heavy iron regulator backpack has been reduced to the size of a wrist watch. The original name of the Denayrouze back pack was ‘REGULATEUR’, the wrist watch size demand valve on this new helmet is signed with ‘MICRO REGULATEUR’.

A sticker on top of the helmet says: PIEL-EFA. Piel is the name of the Piel family, EFA stands for ‘Etudes et Fabrications Aeronautiques’, a company that cooperated with Piel in this project. There are officially 3 different versions of these helmets: the EP100, EP200 and EP300. The exact differences I have not ( yet ) found out though but I will give it a try in this chapter. The helmets are not signed or marked EP100 / EP200 or EP300. The only marking I found is on the MICRO REGULATEUR. As you can see at the close up picture of the regulator on the white helmets ( at the photographs further below ) it is marked ‘Type A100’ In a different document marked ‘Casque EP300’ the regulator is called ‘Régulateur respiratoire M300’ so maybe these helmets were named after the regulators(?) The helmets however have more differences in design the the 3 model names that exist ...

1964. La ‘Société Industrielle des Ets Piel’ ( ‘SIDEP’ ) founded

SIDEP manufactured diving suits, regulators and diving helmets for sports divers and professional divers. SIDEP still exists and is situated in Bretagne, France.

At the photographs here above: an identical helmet but now with a flat faceplate. Photographs David L.Dekker

Initially the PIEL-EFA helmets were manufactured with a round faceplate ( helmet at the photographs here above ) But a flat faceplate is more convenient for diving then a round one because a round faceplate distorts the divers view. Rumors go that the EP helmet with a round faceplate was meant for use with fire brigades ( in smoke and gas ) but I found no evidence for that, in fact does the french navy book explain that in 1969 the EP helmets were improved by giving them a flat faceplate. When the theory of the helmet being named after the regulator model which is built to it is correct then the helmet shown at the photographs here above is a PIEL-EFA EP100, because when zooming in at the regulator it shows that the regulator is ‘Type A100’. But the ribbed ring around the badge indicates that this regulator can be adjusted by the diver himself which makes it an EP200 helmet. According to the french navy book it is the EP200 helmet which has an adjustable  regulator so I think this is an EP200 ... ( when you know better then please let me know, thanks )  Photographs David L.Dekker

An another helmet just like the one here above but now with the flat face plate. Unfortunately I sold this helmet many years ago and I have only got these old snap shots of it so zooming in at the regulator does not reveal the Type number on it. Photographs David L.Dekker

Initially the PIEL-EFA helmets were manufactured with a faceplate that had a chromed frame around it. The helmet at the photographs here below does no longer have that chromed frame. I looked up the original raw file of this photograph to zoom in at the badge of the regulator: would this be the ‘Type 200’? ...

But unfortunately the Type number has not been filled in at this regulator ... The connection between the regulator and the penetrator on the helmet shell now shows a piece of reinforced rubber hose. Interesting to see that this younger helmet still has a round faceplate ...     Photographs David L.Dekker

1966. ‘SIDEP Piel EP100’ helmet.

The USA patent of the Piel-EFA EP100 helmet is dated April 14, 1970 and ‘filed’ in December 21 1967. But in the text that comes with the patent drawings is indicated that the patent was claimed in France one year earlier on December 26 1966. Yves Le Masson and Marcel Pravaz are mentioned as the inventors. Yves Le Masson worked with Piel since the late nineteen fifties, one of his earlier inventions were the  Rebreather Divers Apparatus CFM1 and CFM2 which were also designed by him and built by Piel.

The SIDEP Piel EP100 EP200 and EP300 helmet.

In the book the navy comes up with some impressions about the EP100 apparatus.

The advantages:

  1. -comfort of breathing since the diver does not need a mouthpiece and because of the very low resistance of the demand valve

  2. -comfort of speaking ( since the diver does not need a mouthpiece )

  3. -a large faceplate providing a large field of vision

  4. -the nice futuristic look of the helmet which looks like the helmet of a cosmonaut, which has an attraction which should not be under estimated.

The disadvantages:

  1. -the helmet has an important buoyancy. This makes a complicated system of ropes and straps needed, and extra weights.

  2. -the helmet has a large ‘dead space’. It is never good to respire in a closed space. But according to the constructor of the helmet there is no dead space in this helmet because the regulator provides a stream of fresh air straight towards the divers nose and mouth. So when he breathes he inhales only very little air from inside the helmet.

  3. -in case of a flooded helmet the diver has no oral nasal or a mouthpiece and he will drown. According to the constructor however the faceplate is of a quality which will not break ...

Then the navy comes up with some more interesting details: ‘The helmet EP100 tested by us has well been improved compared to the first version of this helmet which we have tested 3 years ago’. ( so initially the EP100 was tested by the navy in 1966 )

The improvements:

- the round faceplate which caused distortion has been replaced by a flat one .

  1. -the connector where the breathing gas arrives is better designed.

  2. -the functioning of the regulator which can now be adjusted by the diver himself.

  3. -the neck seal has been made longer.

-‘maybe alarmed by the high level of CO2 measured inside the helmet by the G.E.R.S. when testing it early 1969, the constructor imagined and built an apparatus: the Cyclo-Flow’ ... ( the Cyclo-Flow will be described further below )

  1. -‘it must be possible to make the helmet heavier, using a thicker shell or by putting weights onto it to bring the weight in the water to zero. It seems that the constructor is not on the right way concerning this matter’ ...

When looking at the regulator on the helmet shown here above then this variation seems to lack the ribbed ring around the company badge which later models do have. Since the french navy book describes that the EP100 has a regulator which is not adjustable by the diver himself this must indicate that this is an early helmet, the EP100. Also does this early helmet have a chromed frame around the faceplate, the later EP helmets did not have that. The rope that pulls the helmet down passes through the side of the shell. Photograph David L.Dekker Collection

Another early EP helmet with a metal frame around the faceplate. The regulator on this helmet also lacks the ribbed ring which allows the diver to adjust the regulator himself, so it must also be an EP100 helmet. Unfortunately the type number of the regulator cannot be read at this photograph but the regulator is different from the one at the first picture. The micro regulator has a different style of base as the helmet shown at the photograph above this one. This style of base will return on the next variation of micro regulator, the adjustable model with the ribbed ring. At this helmet a small metal chain comes out of the side of the helmet shell, the rope now passes under the helmet shell The diver uses a mouthpiece at this picture, which was not standard in an EP helmet, this was only used to be able to analyze the divers exhaled gas during tests. Photograph David L.Dekker Collection

What is the use of these ropes hanging from under the helmet? These ropes prevent the helmet from floating up. It is an extremely light helmet which will float up when immersed, so it has to be pulled down to keep it on the divers head ...

The SIDEP Piel EP300 helmet.

When we may believe this document then this is the EP300 helmet. The color is no longer white but ( probably ) orange / red. The faceplate has no chromed frame around it any longer. The rope of the ‘pull down’ system passes under the helmet shell. But now the hose between the first stage and the second stage of the regulator or Cyclo Flow passes through the right side of the helmet.  Document David L.Dekker Collection.

Here the book describes the differences between an EP100 and an EP200 helmet: ... ‘The goal of these tests is to see if the ‘Cyclo-Flow’ device can reduce the level of C02 inside the helmet. The helmet EP100 has an important dead space: 1.750 ml. When diving on helium oxygen the regulator needs adjustment, the diver was not able to do that himself and needed the help of his buddy to take care of that. On the EP200 helmet this problem does not exist, there the diver can adjust the regulator himself, also has the EP200 helmet a smaller dead space’ ...

The SIDEP Piel EP100 vs. the EP200 helmet.

In my library I have a book which was published by the Marine Nationale ( French Navy ) in march 1970. The entire edition of this book was 5(!) copies. The books is in fact a test report of the Piel EP100 helmet equipped with the ‘Cyclo-Flow’ device. The Cyclo-Flow is an apparatus used to create a return line when performing deep diving on helium oxygen mix ( pls read the ‘La Spirotechnique Diving Helmet’ chapter to learn more about deep diving and the use of the ‘return line’ ) This book reveals some interesting observations. With the book I have a letter written by monsieur Piel himself to the French Navy ( G.E.R.S. 83-Toulon ) which is in fact the receipt for a supplied EP100 diving equipment and a ‘Cyclo-Flow’ apparatus. The letter was sent on the 9th of June 1969 from Etampes where Piel was based at that time. Monsieur Piel asks the navy to return the equipment before the 1st of July, it seems to be supplied only to do some tests with it. The first thing we learn from this letter is that in June 1969 Piel still built the EP100 helmet.

The SIDEP Piel ‘Cyclo-Flow’

As indicated in the french navy book:

-‘maybe alarmed by the high level of CO2 measured inside the helmet by the G.E.R.S. when testing it early 1969, the constructor imagined and built an apparatus: the Cyclo-Flow’ ...

The Cyclo-Flow receives breathing gas at 7 to 8 bar over ambient pressure which it supplies to the micro regulator on the helmet. The return line is connected to the exhaust valve of the helmet, passes through the Cyclo-Flow and goes to the bell where it is filtered and enriched with fresh oxygen. The return line is operated by the difference in depth between the diver and the bell which should be between 5 and 15 meters ( 0,5 to 1,5 bar ) Would the diver swim above the level of the bell then it becomes difficult / impossible for the diver to ‘blow’ the exhausted gas back to the bell, but then the exhaust valve lets escape the exhaled air out of the system into the water. See illustrations here above.         Document David L.Dekker Collection.

The SIDEP Piel ‘Cyclo-Flow’ according to the French Navy

The ‘Cyclo-Flow’ was tested and the following notes were made:

  1. -when inhaling the exhaust valve is closed and only the micro regulator works.

  2. -during the short moment between inhaling and exhaling a small quantity of gas escapes through the exhaust valve. This creates a light under pressure inside the helmet which activates the micro regulator providing a ventilation of the helmets dead space and reduces the Co2 level.

  3. -When exhaling the micro regulator is closed.

  4. -the functioning of the system depends on the adjustment of the micro regulator. During the tests the sensitivity of the micro regulator was reduced which created a continuous flow from the regulator to the exhaust valve.


- the helmet PIEL-EFA EP 100 which has been tested by us has a large dead space and should, according to us only be used in combination    with the Cyclo-Flow devise. The concentration of C02 in the dead space would get to high without this ventilation.

  1. -equipped with the Cyclo-Flow and breathing air the evacuation of Co2 is not 100% and could become dangerous.

  2. -equipped with the Cyclo-Flow and breathing helium-oxygen the evacuation Co2 is very good but still depends on the fine adjustment of the micro regulator. The breathing comfort is convenient.

197?. The SIDEP Piel ‘Bulle CA 101’ ( Bubble ) helmet, with Cyclo Flow

Last but not least: the Piel SIDEP ‘Bulle CA 101‘ helmet. I never saw one for real, all I have on this helmet is this document which unfortunately is not dated.  It comes close to the EP helmet. According to the document it can both be used on land and under water.         Document David L.Dekker Collection.

Above: the original drawing which was used as an illustration in the french navy book. Document David L.Dekker collection

Above: two original drawings of the Cyclo-Flow. Both drawings are dated 1973 and signed by YLM, 4 years after the first Cyclo Flow was designed by Y. Le Masson, built by Piel and tested by the French Navy. Documents David L.Dekker collection


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