Draeger Dolphin Modifications

for Deep, Cave, and Trimix, semi-closed and closed-circuit rebreathers



Page IV Generation 8 

The current configuration.  New O2 block and PO2 monitor

Page III - Generation 6

Addition of manual diluent add valve.

Page II - Generation 5 Some more rebreather links

The journey begins here:

Very early on it was obvious that the standard unit wasn't going to be adequate for the diving we do.  We tried several configurations of the Draeger unit trying to address our concerns.  None of them addressed our concerns for deep (75 msw (240 ffw)) or cave penetrations.  My dive buddy Steve Parker came up with the aluminum mounting unit with switchblock and I made some turtle shells.  The pictures below illustrate the results as well as further developments.  There are two of these units.  In semi-closed mode they have been used down below 60 msw (200 fsw) and for 2+ hr cave penetrations.  They have been used with both nitrox and trimix and in a wide range of temperatures. (0C to 30C)  Our main concerns all along have been that most SCR and CCR units out on the market do not offer adequate OC bailout capability from deep dives and are frowned on by the cave diving community in Florida.  Our first major modification was for a SCR system that met our safety concerns.

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Basic modification - Dual 45 w/crossover and homemade turtle shell

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Switchblock for oxygen deco CCR.  Oxygen is carried as a 40 cf. (6 l) stage with quick disconnect

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Unit is used with standard backplate assembly. Cylinder on right is argon suit inflation.  On the later unit this is the oxygen supply for the doCCR.

There are a number of individuals around the world who are doing major modifications to the Draeger Dolphins and Rays.  It seems most are interested in either changing the depth range or duration limits of their units.  I would like to mention a few of them here.  Kerry McKenzie of Australia, Jean Michel Urbani of France, Peter Kruze of Germany have all had some good input in the exchange of ideas for the search of the perfect affordable safe rebreather. 

The approach a lot of us have taken is the dual orifice closed circuit rebreather along the lines of Gordon Smith's KISS rebreather.    Why go the the KISS approach? 

Well  Dave Thompson, original designer of the Inspiration CCR, put it very well.  He said;   "The bad thing about manual CCR's is you "need" to drive them, and to a degree that's task loading...   The good thing is you KNOW that if you don't, you will die. It focuses the mind.

The good thing about electronic CCR's is you don't need to do anything because they drive themselves. The bad thing about electronic CCR's is they MIGHT go wrong, and you MIGHT not notice it because you don't need to do anything right!!!!"

I believe that from a philosphical point of view it is better to accept the limitations and task loading of a manual CCR to gain the experience and intimate knowledge of your metabolic needs.  Then, if you wish to proceed beyond the limitations of a manual sytem, you can invest in an electronically controlled system.  You will have most of the experience and knowledge to subconsciencally monitor the automatic systems functions.  

When does a Draeger Dolphin cease to be a Dolphin?  Well it has to be sometime between jettisoning the Draeger BCD and going closed circuit.  I now own a closed circuit rebreather made up of Dolphin pieces.

I converted mine in september of 2001 and it has gone through several modifications since then.  These modifications are very impressive to dive.  The first modification was to install a manual O2 injection valve.  This was first tried by Kerry McKenzie.  This works well, but takes a great deal of attention to dive.  The second mod was to add a supply line for the O2 to the injection block for a continuous supply O2 via the O2 orifice at a reduced pressure and using a constant pressure regulator.   This allows a low O2 feed insufficient to maintain metabolism but enough to cut down in the frequency of manual addition.  This is the principle used by the KISS rebreather.  

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Manual O2 add valve

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Detail of CCR mod KISS/McKenzie first generation CCR


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Dual orifice CCR (DOCCR)  2nd generation CCR

You can follow the natural progression in the search for the perfect rebreather.   The second modification was the development of the dual orifice CCR (doCCR).  It uses the existing Draeger orifices (as before) but mounted on the switchblock assembly.   The output of the orifices then feeds a common line to the exhaust (input) side of the scrubber.  This allows a better mixing of the oxygen with the normal flow of gas through the loop.  The third step was the elimination of the Draeger orifices and replacing them with commercial units for a more compact package and the ability to get to the 70 m range with sonic flow.  To do this a smaller orifice than the Draeger O2 (pool) orifice was needed.  The units I used are from Bird Precision and have dual 40 micron filters.   I am using two oxygauges for PO2 monitoring.  (Jump on the link for a paper on why I settled on two sensors)

Oxygen for the unit is supplied by a 13 cf. (2l) pony bottle strapped to the side of the dual cylinders.  This is enough O2 for over 5 hrs with reserve.  Argon, when needed is a 8 cf. (1 l) bottle strapped to the other side.

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Close-up of switchblock and Draeger orifices with adapters

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Cylinders upside down.  Can reach all valves easily

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Closeup of switchblock with Bird Precision Orifices.  More compact Third generation CCR



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Oxygen injection unit fourth generation

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Closeup of connectors and O2 injection.  Fourth generation CCR.

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Fourth generation - cleaner left side for offboard deco gases

With the fourth generation, I have eliminated the switchblock and installed some stainless hydraulic connectors.  These give the possibility to switch diluent gases on the fly.  The hoses are both color coded and mechanically identifiable as to content.  The switchblock worked well but cluttered my side and was not easily visible.  The connectors have restored a fuzzy feeling I like when I dive.  I have added another page which gives detail pictures of the Generation 5 unit.

I have also made a second stronger turtle shell for intermediate depth diving.  It has been dove with the normal 4 l (30 cf.) cylinder and a 1,8l (13 cf.) oxygen supply.  We plan on adapting this to a configuration very similar to Kerry's unit except with 4 l (30 cf.) cylinders for diluent and O2 supply.  Depth range for this configuration is approx. 45 msw with durations of less than 10 mins O2 deco.   Carrying an extra 4 l cylinder in the normal butt mount will extend the deco limits.  All the designs have been made with the OC bailout worst case scenario as a primary consideration.  The advantage of this setup is it is lighter.  In a two day period I managed 5 1/2 hours dive time and never changed a cylinder!  Depths ranged from 15 - 25 msw.  What a great way to dive!!!

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mod for any backplate BC

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weight - min 8 lbs for CL's

And now the diving.  We would never have had to go to these extremes if we dove as my wife prefers, warm and shallow.  Well the pics kind of show what we have to dive.   I say have to dive because diving is an addiction.

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Getting out from an ice dive

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Just a fun dive

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Just fun

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