IDA-72  SCR Conversion to MCCR project Conversion done by Johan Pretorius


1st things 1st and thanks, honours and credits to those that deserve it.


I got most of my inspiration and all my theoretical knowledge on the IDA-72 from Dave’s “nobubble” site, the work he did for other IDA-72 divers and for that I must thank him. LINK:

A lot of the modification ideas were bounced of my good friend and dive buddy Monty Guest, who understands Rebreathers probably the best of all the people I know personally. He had to endure many hours of listening to some silly and some not so silly ideas, helping me keep a sane mind during the modification process.

My father who assisted me in the modification process, although not a diver himself, his simple logic, insistent questioning of my thinking and reasoning, as well as his ability to do magic with limited tools, helped me resolve many of the issues I got stuck with.


This is my documented effort to convert a Russian manufactured Deep Water Umbilical Supplied Heliox SCR (Semi Closed System rebreather) named the IDA-72 to a MCCR (Manually Operated Closed Circuit Rebreather) with Trimix capabilities. I tried to keep the system as original as possible, so as not to lose the essential character of the machine, although the machine’s working character had to be completely changed for the process to be successful. (If that mumble makes sense to anybody?) The main reason why I chose the IDA-72 as my rebreather of choice is very neatly summed up in the following paragraph, taken from Dave Sutton’s website.


“The Russian IDA-72 is a rather unique Semi-Closed Circuit rebreather designed to be fed by an umbilical for surface-supplied or saturation diving using Heliox. It has  2 x 2-liter internal cylinders that were originally designed to be used as bailout cylinders in case the umbilical supply was lost, a very large scrubber capacity, and an extremely interesting belt-worn valve block that allows the diver to flush the loop and also to split the loop and cause the rig to become a demand-only system. This last feature is totally unique as far as I can determine, and is a very interesting design feature. This feature alone makes the IDA-72 worthy of close study.”  - Dave Sutton


This meant that with some clever modification, I can have a Closed Circuit Machine, designed to work at 200m depth, with a belt block that allows me to effortlessly flush the loop with dilluent, and the ability to switch to an Open Circuit demand system, with the flick of a switch.


I am not going to give a tear down of the machine in stock standard format, as this info is already excellently documented by Dave Sutton, and the info can be viewed on his website at the following address:


A quick visit there will acquaint you with the workings of the original stock standard IDA-72 and can help understand how and why certain systems work.

The machine will offer the following inherent and added safety features when completed:

  • Guaranteed deep water rebreather capability.
  • Built in BOV (Belt switch block to Open Circuit mode).
  • Quick and effortless loop flushing.
  • Add a FFM with additional bailout plugged into one of the side P-ports (For sanity nose breaths and possible Oxygen-Toxing)


Here you have what I believe, is the safest Rebreather system available (not on the market today).

Works for me…….


Stripping the machine


Not a very nice time for me….Having to remove the heart, or is it guts, of the machine?…

But, all parts were safely kept, with as little as possible damage done. I tried to keep the machine as original as possible, but some stuff had to go….

What I ended up, is basically a bare chassis, with a breathing plenum and what I call the dilluent injection array consisting of an inlet connector with OPV and two pipes that will feed the breathing plenum and allow for operation mode switching.


But, I had the basis of my MCCR rebuilding plan.


The huge chassis of the machine lends it self to various opportunities and possibilities, and I had to really keep focus on hat I wanted to achieve. Don’t be fooled, the scrubber that goes into the cavernous chassis is HUGE.


The breathing plenum on the left, with the two pipes that will be supplying pressurised gas for mode switching. The original cylinder belts are still in place and will be used as is. The snakes’ nest that is supposed to be found at the bottom has been removed, as it will unfortunately not form part of my conversion idea.     


Diluent injector array and gas plumbing


The IDA-72 is very cleverly designed. It was designed to be fed by an umbilical from a diving bell or similar type of set-up at extreme depths. This meant that the IDA-72 had a very smart dilluent connection system, to ensure the dilluent got to all the important places. I decided to keep the system as unchanged as possible (mostly). Unfortunately I had to remove the female umbilical connector as the male part is in Russia somewhere, probably attached to a nuclear submarine of sorts.


I opted to put in a Quick Connect system, with the female Quick Connect on the Dilluent supply and the male Quick Connect on the rebreather. The Umbilical connection has an “interesting” thread size, and I had to source an adapter to fit the connector, which ends in a ¼ inch push lock barb. An alternative would be to drill and tap the female connector, so that a ¼ inch barbed fitting screws into the machine. Not having a ready available means of doing this work, I opted for the adapter which meant that I could use off the shelf parts.



Due to the possibility of using off board dry suit inflation, I needed to move the dilluent connector as high up the rebreathers as I could. The dilluent connector has its own proprietary overpressure valve that protects the system against over pressurisation.


The parts of the Dilluent connector adapter


I used silver solder to permanently fix the parts of the dilluent injector adapter, so as to minimise possible failure points


The dilluent connector adapter polished and installed. Note the proprietary over pressure valve


The Quick connect and ¼ inch hose installed. Note the Ferrules used to clamp the hoses additionally to the gripping power of the Pushlock barbed system. A bolt snap on the male QC is to secure the QC when not connected to the Dilluent supply. The original position of the dilluent injector can be seen to the left of the current one


Important to keep in mind, is that the dilluent not only serves an important purpose on the breathing gas side of things, but also drives the important features of the machine. I had to route the gas supply from the dilluent connector to all the important parts in the rebreathers. To be able to do that, I needed to build a manifold that could withstand 11 bar interstage pressure, with enough outlets to ensure that all the parts that need gas, can receive it.

Below is a picture of the dilluent manifold, with a numbered sequence. The numbers are for explanation of what each pipe does.

  1. Dilluent in – the dilluent comes into the system via the umbilical connector. This is the main feed to the dilluent supply
  2. Quick connect barbed fitting – Used for wing inflation. I attach a ¼ inch hose with a connector to attach to the power inflator of my wing
  3. The supply to the built in 2nd stage Demand valve. This demand valve doubles as a ADV, which keeps the counter lung from collapsing on descent as well as an Open Circuit Demand Valve, when the unit is switched to Open Circuit mode
  4. Quick connect barbed fitting. This is the fitting that will be supplying my bail out regulator / FFM with bail out gas. A ¼ inch hose is connected that ends in a 2nd stage DV or alternatively a DV with a P-connector, to fit my Drager FFM
  5. The supply to the gas Plenum / belt switch block, which splits the loop into Open Circuit if activated.

The Oxygen supply and routing


The IDA-72 originally has two x 2L onboard Trimix cylinders rated at 200 BAR. These cylinders are ideal for use as the IDA-72’s onboard Oxygen supply, (and therefore the colour change, black & white is the legal colouring for Oxygen). To effectively use the smaller cylinders in conjunction with the large scrubber, I opted to have a manifold manufactured to connect the two internal cylinders. The manifold then allows a capped DS4 to be connected. This gives me a few options for future use.

  • I can use both O2 cylinders internally, giving me effectively 4L @ 200 BAR which is 800L of oxygen (maximum pressure). Plenty oxygen for the long deco dives that are hopefully on the cards
  • I can discard the use of the manifold and use one internal O2 cylinder and the other cylinder as an internal dilluent cylinder. Each cylinder will have its own 1st stage supplying gas to the system. The plumbing change is quick and easy. All the gas will then be onboard, and the diver will then only carry an off board bailout, as a stage /sling cylinder.
  • For dives deeper than 80m, the system allows for the discarding of the oxygen manifold, and installing of a depth compensating 1st stage on the one cylinder in conjunction with a manual add valve and using the capped DS4 for the CMF on the other cylinder. When the CMF stops working at +/- 80m (theoretically) the user will be able to manually add Oxygen to the system via the 2nd depth compensated 1st stage, effectively turning the oxygen supply into a demand supply. On ascent the CMF will take over the Oxygen supply when the pressure decreases, this will also offer redundancy in the Oxygen supply for dives involving long decompression.


I noted that Copper Oxide (the green stuff you see on copper and brass fittings), may become a problem in future. The alternative is to have the brass and copper parts chromed. That will be the final step in the completion of the system


Close-up of the IDA-72 BIG scrubber in place with the Oxygen manifold and DS4 1st stage


Close-up view of the Oxygen manifold and capped DS4 The blue scrubber is a IDA-71 scrubber with a slight modification


The Oxygen manifold and installed DS4 1st stage is clearly visible, with the CMF on the right hand side of the table. The male QC for the dilluent supply is visible on the left hand side of the SPG


Close up of the gas supply system. On the left is the Dilluent manifold, Bottom is the DS4 and the Hydrogom CMF valve. The hose on the right is the Oxygen addition to the counter lung from the Hydrogom valve. ; note the copper oxide already forming on some brass parts. Chroming of the parts may be a solution


PPO2 Monitoring

The mantra of all Rebreather divers.. “Always know your PPO2”

Although the MCCR IDA-72 uses a CMF (Constant mass flow Valve) to bleed Oxygen into the loop, it is still vital to be able to monitor the PPO2 in the system, so that the diver can make the necessary adjustments to the gas he/she is breathing.


A rebreather is in effect a Nitrox / Trimix factory carried on the divers back. Using the same tried and tested method used in the conversion of the “Franken-son” and relatives; I opted for installing a P-connector system and independent PPO2 monitoring.


The question has always been how many PPO2 displays do you really need?

I opted for a very simple solution to this perceived “problem”

I installed only two independent PPO2 displays, and my diving philosophy is simple. If at any stage during the dive, both PPO2 monitors do not give me the same reading, I bail out and do an ascent on bail out gas, which I carry in an AL-80 cylinder as a sling / stage cylinder. No discussions, no loop flushes, No funny stuff. It is just not worth it. – rather come back tomorrow. If my dive buddy has a problem with that, I will find a new dive buddy.


Two independent R22D Oxygen cells do the monitoring and the displays are read from two independent monitors.

I am utilising one home built PPO2 display, that a friend of mine makes, and the second is my VR3 dive computer that doubles as PPO2 verifier and deco calculator. To solve the problem of two cables coming out of the machine, and lying everywhere except where they should, the cables are fed through 25mm tubular webbing, which protects the cable and helps with clean neat routing.


The two Drager female P-connectors installed in the counter lung. The Oxygen inlet can be seen protruding just under the right Counter Lung attachment


Two independent PPO2 monitors (VR3 & home built)


PPO2 monitoring installed. Tubular webbing can be seen ensuring neat routing and protection of the monitor cables


Scrubber Modification


The IDA-72 has a HUGE scrubber. It must be seen to be believed. It holds approximately 5 Kg of sorb, with dimensions that are about as big as a shoe box. The 5 Kg of sorb should be equal to about 5+ hours of continuous diving in our cold Atlantic water, although your mileage may vary.


This is a complete overkill for most sport diving, but the unit was originally not designed for sport diving. It was designed to handle the gas volume at 200m which is equal to 21 BAR absolute pressure, when the diver engages the Trimix bail out option.

This meant that using the BIG scrubber exclusively, would result in a waste of sorb, as I am not a great fan of re-using and leaving the same sorb in the scrubber for too long, as it is cheap enough to warrant often change (well.. cheaper than a life, definitely !)


The IDA-71 has a very efficient scrubber canister, which holds approximately 2.1 Kg of sorb, which is more than adequate for a weekends’ rebreather diving to depths less than 30m.

I decided to have an adapter made up, to allow me to use the IDA-71 scrubber with the IDA-71. A straight forward fit is not possible, as the scrubber connection hoses of the IDA-72 are of a much larger bore than the IDA-71, even though they have the same type thread.

The adapters were turned up from Delrin which screws down on to the IDA-71 scrubber, and fits the IDA-72 scrubber connector hoses.

This allows me to use a smaller and lighter IDA-71 scrubber for normal shallow water diving, but still allowing the full use of the machine’s BIG scrubber for serious deep or long dives, should I choose to use it.


IDA-71 scrubber with adapter to fit IDA-72 scrubber connector hoses


Close up of IDA-71 scrubber with adapter to fit IDA-72 scrubber connector hoses


Scrubber connector’s fitted to the IDA-72 counter Lung


IDA-71 scrubber fitted into IDA-72 chassis with scrubber adapters in place


IDA-72 with Oxygen manifold, DS4 and BIG scrubber in place. Gives an idea of size of the scrubber


Breathing hoses


The IDA-72 has an interesting proprietary hose system. It consists of a huge outer hose that serves as a warm water jacket for the breathing hoses within. The purpose was to warm the divers gas (Heliox) for breathing purposes. This system is totally unsuited for sport diving, and had to be changed, unfortunately.

The inner breathing hoses are spiral hoses that are quite stiff and may be difficult to dive with, if not connected to a helmet of some sorts. At a later stage I will be connecting my Drager Panorama Full Face Mask to the IDA-72 and the hoses might be used.


For my current diving needs, I opted to use Drager Ray hoses as they are easily found and a pleasure to dive with.

The inner diameter of the Drager hoses is also a 100% fit over the proprietary breathing hose connectors that come with the IDA-72.

I used jubilee clamps (Stainless Steel hose clamps) and tubular webbing to secure the connectors to the hoses


The Drager Ray breathing hoses with the yellow IDA-72 hose connectors


Up close of the hose and hose connectors. Note the SS hose clamp and tubular webbing


Drysuit inflation system


Due to our cold water, and taking into consideration the types of dives that are being planned with this machine once it is completed, a separate drysuit inflation system will be needed. It would have been easy to add an additional hose from the manifold, or tee-off the wing LP hose to include a dry suit inflation hose (another idea ) but due to the fact that Trimix can and will be used in the machine, it is not such a great idea after all, as Trimix is not known for it’s insulation properties.

This means that an independent system must be put in place.


The system consists of a set of “G” clamps and my IDA-71’s 1L Oxygen cylinder and a Drager Kleinkonisch pillar valve.


The female “G” clamp is secured to the IDA-72’s chassis with recessed machine screws and nuts. Care was taken to ensure that all the dissimilar metals were “insulated” so as to prevent dissimilar metal corrosion. The IDA-71 cylinder neatly slides into the female “G” clamp and a Drager Kleinkonisch pillar valve does the rest.


The cylinder colour (light blue) is close enough to our legal colouring for Argon, which is referred to as Peacock Blue.

The cylinder sits on the left hip, behind the wing and will be filled with either Argon, or Air and will have its own 1st stage regulator.


IDA-71 Oxygen cylinder with male “G” clamp


Female “G” clamp on the left side of the chassis. Note the blue PVC inserted and neatly trimmed following the edges between the “G” clamp and the IDA-s body, to prevent dissimilar metal corrosion


The drysuit inflation cylinder installed, ready to go, just add 1st stage


Wing and harness


The IDA-72, like the IDA-71, is contoured to fit the divers back profile. It is therefore very difficult to attach a stainless steel backplate to the IDA-72.

The proprietary harness that came with the IDA-72 is incomplete, which I believe it to be the case, rendering it basically useless for our use. So it had to go…


By inserting strategically placed 6mm stainless steel bolts, an Oxycheg “O” pack can be bolted securely to the back of the IDA-72. The “O” pack is a soft, but very strong nylon backplate that is perfectly suited for the purpose.

The wing is a 50Lbs (22 Kg) lift double tank wing that provides more than adequate lift for the machine during a dive.


The harness is in the Hogarthian gear configuration, leaving ample place to attach bailout cylinders, dive lights etc


Harness webbing and soft “O” pack


6mm Stainless Steel bolts and nuts to secure the webbing harness, once again all dissimilar metals have been “insulated”


Bail out regulator / Full Face Mask


Currently the Machine has a bungeed bail out regulator, which is fed from the Dilluent manifold. It is not the ideal solution, but as with most works in progress, it is a start. It is important to realise the shortcomings of the system, although the ability to switch to OC mode is a great asset, inherent to the machines original design.


I plan to do all my rebreather diving with a FFM, and to be able to use the FFM, the following modifications have been done.

The IDA-72 DSV is a very nice designed piece of equipment but it is definitely designed to fit onto a helmet of sorts.


I decided to use a FFM with the IDA-72, and possibly utilising the proprietary DSV and spiral hoses, if the hoses prove to be comfortable to dive with. Doing this would serve the purpose of adding more of the original flavour to the diving machine, without increasing the conversion costs.



IDA-72 DSV view from the front. The metal ring can be seen, with thread, meaning that a connector from a diving helmet must have screwed onto the DSV


IDA-72 DSV viewed from behind. Note the big turning knob.

(DSV = Diver Surface Valve)

The movement of the DSV is fluid and is a half turn to either side for open or closed positions. Unlike the Dräger DSV, there is a large “hooded” vent on the top of the DSV. Opening the installed DSV to surface air, makes breathing thought the FFM and installed DSV very easy.

The DSV was definitely not designed to be removed from the helmet during diving, as you would do with a normal DSV in case of a bail out scenario. That would explain the need for an OC bail out function, such as provided by the Belt switch Block.  So does form follow need or visa versa?


As the machine did not come with a helmet (probably stored on the same Nuclear submarine of sorts as the male Umbilical connector) I had to turn to invention, to solve the problem of making all the parts fit.

An engineering company who are always eager to help us divers with our little projects turned a DSV-P-Port connector and a locator ring based on my description.


The prototype DSV – to - P-port connector and locator ring


The DSV – P Port connector installed in the IDA-72 DSV ready to be mounted in the Drager FFM


Not having a ready supply of Drager Shark regulators, or a convenient C&C milling machine, I had to come up with an idea of how to convert a normal SCUBA 2nd stage DV to a DV that will be able to connect to the Drager Panorama FFM.

I had shortened male Drager P-port adapters turned from Delrin (Acetal) that would serve the connecting purposes.



Turned up shortened Dräger male P-port connector



The P-port connectors were mated to a normal SCUBA DV with the use of a file and some “Pratley Putty”, which are two chemicals, in the form of pliable “play dough” sticks, that once combined in equal quantities, after 10 minutes or so, becomes rock hard and NEVER lets go.


The file was used to take the edges of the oval connector where the SCUBA bite piece is cable tied on. This resulted in a 100% fit around the sides, as the round P-connector is fitted over the SCUBA DV mouth piece.

The Pratley Putty sealed the flat sides of the oval mouth piece and is responsible for holding the system in place.

I tried to dislodge it, but found it cannot be done, not without some serious use of excessive power and maybe tools


The P-port installed on the SCUBA DV


Close up of the inhalation side of the DV. The Pratley steel can be see around the oval opening, keeping the system together


All that is left is to install all the elements and bring the system together.


The DSV installed on the Dräger Panorama FFM

I would like to thank Johan Pretorius for sharing his project with us!
If you have any questions don't hesitate to contact me
published 01-12-2008

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Johan Pretorius rebuild the Russian IDA-72 to a manual operated closed circuit rebreather. He modified the scrubber system in such way the rebreather can be used for both short and long dives. He also changed the loop to fit a full face mask. Here you find his detailed description

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