Universal Rebreather


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 Siebe Gorman’s Universal Breathing Apparatus

Date: 19 January 2003

Royal Navy C.D.B.A (Clearance Divers Breathing Apparatus)

JW. Bech


Siebe Gorman and Co. Ltd



Universal Breathing Apparatus

 used on human torpedo's

Land of origin



Special Note: 

Variant of Amphibian


User group



Part no:



Working principle

CMF constant mass flow


Gas type



Cylinder volume



Max. cylinder pressure



Material of cylinder



Counterlung inspire

On the chest


Counterlung exhale



Dive time duration

Depending on the nozzle


Operating temperature



Magnetic signature



Weight ready to use in Air



Weight ready to use in water






Scrubber material

Bariumhydroxide/ Sofnolime









Scrubber+CL+Emergency cylinders on the chest

Weights and Cylinders on the bag


Single hose with shutt off valve

Pendulum principle


Weightbelt (balls)



Exhaust valve mounted in front of the wearer on the left shoulder.











If you have any information to add this sheet please mail it to jw.bech@quicknet.nl References to source and names will always be added!  


Info found: R.H. Davis, Deep Diving and Submarine operations
And Dave Suttons Beautiful report on: http://www.nobubblediving.com/cdba.htm


Origin: http://www.therebreathersite.nl


Info: jw.bech@quicknet.nl





The "Universal" is a variant of the "Amphibian" apparatus; it is on the same regenerative principle, and has the same triple-purpose uses. It is designed so that it may be adapted to the requirements of special operations, e.g. it may be used as an ordinary shallow­ water apparatus with continuous oxygen supply, or for clearance diving or similar deeper work it may be altered to supply oxygen/nitrogen mixtures or, thirdly as a breathing apparatus for use in poisonous atmos­pheres. It consists of:  two oxygen cylinders joined together, one of them being fitted with a special neck extension on which the main supply control valve, automatic reducing valve, by-pass valve and supply tube to breathing circuit are fitted, with the object of ensuring the valve group being completely under the control of the diver, the whole arrangement as originally designed and patented by H. A. Fleuss and R. H. Davis; water-tight breathing bag containing:  CO2 absorption canister of the radial design as originally made by Siebe, Gorman & Co. Ltd., for diving apparatus known as the "Human Torpedo" type; flexible rubber hood, and facepiece with full­vision window;  mouthpiece and nose-clip; com­plete diving dress;  lead weights arranged for quick-release, partially or wholly, for buoyancy and ascent to surface; suitable harness for carrying the apparatus.





The CDBA (Clearance Diver Breathing Apparatus) was and still would be a safe, practical and operationally capable set, if we had spent some time evolving the set like the fore-mentioned engineering designs. While I have a high regard for the scientists and engineers who design and build new and high tech sets, I don’t believe new is always better. I retired as Chief Diver/Unit Chief Warrant Officer from DCIEM (Defense and Civil Institute for Environmental Medicine) during the CUMA (Canadian Underwater Mine countermeasures Apparatus) and the CCDA (Canadian Clearance Diver Apparatus) development program. While not having much input into the program I did share my concerns with the diver friendly application of the sets. Not forgetting what it is like diving out of a Zodiac, crawling about the beach at night, swimming, looking at a compass, depth gauge and looking after your buddy, seemed like enough things to do whilst diving. This is where I reflect, at the potential missed using the CDBA.

Some times Engineers get it right! This works for me when I remember the CDBA. If only we had used the available O2 and CO2 monitoring technology, which was available in the 60’s and 70’s and changed the way we used the set, we might still have the Ole Reliable CDBA set with us today. It is my hope that this article will stir up some good memories, comments and debate with all the levels of participants in the worlds diving community.

Now, to get to where I want to go with this and generate interest, please allow me to go back in time when I first dove the set and see how a few changes would allow this old diving set to evolve and be as practical today as any other diving set.

1966 when undergoing training for the CD2’s course (TQ5A) divers did an 8-week phase with CDBA rigged for O2. This was followed by a 2-3 week phase using mixed gas. It was during this period we learned? About the gas laws and how they effected the diver. I think most of us memorized the laws instead of understanding them. This was certainly the case for me. Remember this was still a “do as we say navy”. We followed the BRCN 5350 to the letter (most of the timeJ). And if we paid attention to what we were doing we usually had an uneventful dive. Now to appreciate where I am going with this .It would help to go through a typical O2 dive using the CDBA set. This would allow the reader to appreciate the physics and the physiological effects to the diver. Also, during this part we won’t do any of the engineering changes, only, operational procedures will be changed. Maybe another article with engineering modifications would be interesting.

With the set charged and the diver dressed, the sequence would go like this:

1. Purge the (CL) counter lung, turn on O2 using the by-pass valve, and fill the CL. Breath pure O2 for one min. Set was rigged for O2 to flow at 1.5 Liters per min.

2. Purge the CL again, by-pass to inflate with pure O2 and enter water. Note: diver at this time is exposed to O2 at a PP (partial pressure) of 1 ATA (atmosphere Absolute).

3. Diver descends down to the long jackstay at 33 ft. or 10 meters keeps the CL full using the O2 by-pass valve. Note: The diver is now exposed to O2 at a PP of 2 ATA.

4. During this dive, the diver would swim underwater around the jackstay (for me it was about 9-11 Min’s J) the depth would range from 33 ft to 15 ft so the diver would be exposed to a PP O2 of between 2ATA to 1.5 ATA. Most dives were uneventful. Some were not. One of my students during the same type of training experienced an O2 hit, as did others over the years.

So! What do we know from all this?

The average amount of O2 consumed by a moderately working diver is approximately 1.5 liters per min. We also know that this rate does not chance. Example, A diver working at 165 ft still uses approximately 1.5 liters per min. surface equivalent. So the counter lung stayed at 100% O2 no matter how hard or little they worked, or guffed off.

The reason we stayed on O2 for one min ranged from,(Lwe were told) This will see if you have a negative reaction to O2, or, to, this will remove some of the N2 still in your body and set. Today the only operational people I know who pre-breath O2 is Astronauts and Pilots of very highflying spy aircraft. Thus avoiding altitude bends. I have never heard of any one having a negative reaction to breathing pure O2 on the surface. One has to remember this is what the Diving Manual BRCN5350 dictated, so, this is what we did. Ours was not to reason why? Ours was just to do and whatever!

Since those days we have developed the PPO2 / Time /Depth Exposure tables, so now we can better understand the effects of gasses on the diver. So let’s do the same training dive, changing only the way we dive the set, and instead of O2 in the emergency bottle we put in air.

Note what happens!

With the set charged and the diver ready, the NEW dive sequence would go like this:

1. On Gas, reducer set for 1.5 liters per min., inflates CL with air, enter the water, and dive to the jackstay @ 33 ft /10 Meters. Diver inflates CL with emergency bottle to compensate for depth. Diver swims around jackstay runs out of gas returns to the float.

SO! What happens to the diver, with the changed SOP’S?

The diver turns on the set and starts in-putting 1.5 liters of O2 per min. The diver inflates the CL with air. This is made up of approximately 20%O2 and 80% N2. Now the diver is exposed to O2 at a PP of .2 ATA. Every thing is OK!

Diver enters the water and goes to 33 ft, filling CL with air to compensate for depth. At depth diver is now exposed to O2 at a PP of .4 ATA. As long as the diver swam using the 1.5 liters per min the PPO2 would remain the same. The only thing, which would change the PO2, would be the physical absorption of the N2 into tissue. All the rules pertaining to swimming to fast or to slow would apply.

This may seem all so simple. And maybe it really is.

However, think about it, if, we dive using this same scenario there would be no depth restrictions, except for decompression, (theoretically). As long as the diver uses the gas and bypasses with air. The PPO2 should not change; at 132 ft. or 4 ATA the PO2 would be .8ATA. At 297 ft or 10 ATA the PPO2 would be 2ATA, which is the same as pure O2 at 33 ft.

Using the gas laws to demonstrate the increased effectiveness of the CDBA set is only the beginning of how to improve what the engineers got right away, back when. I have a swim set in my,” I Love Me Room” and it always challenges me to look at what we did not do with a set, which done me proud. I also believe that there would be more divers still diving today, had we evolved the set as it should have evolved. When I think about the LARV1 A5800, CCR1000, CUMA, CCDA, MK5 modified, SL 17 and KMB9 I think they are all great technical advances for the diving community. The CDBA Modified would have kept them all honest and harder to fund, because SOMETIMES ENGINEERS GET IT RIGHT.

This is just a quick overview of what I believe the CDBA could do had we understood it or tried to improve it. It would be interesting to hear the views of others who dove and appreciate the CDBA set. I am quite confident that divers can develop diving sets just as well as engineers. If there is any interest, please drop me a line at: opaoma@direct.ca Submitted by Milt Skaalrud

Published with permission.





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