Use a gag strap?

[stuartv]

Stuart, really great to see Mares offering the safety upgrade for the unit.

Whats the WOB in CC and OC modes of the BOV; what sort of gag strap is fitted to it?

I do not know the WOB numbers. My contact at rEvo HQ told me that the CC WOB is lower than the WOB on the stock DSV (the Drager). I did not ask for #s.

It uses the same mouthpiece/gag strap assembly as the stock DSV.

 

[Tassi Devil Diver]

The kit I was offered includes the BOV with all the fittings needed to re-use the stock, rubber breathing hoses, and a LP hose that is long enough to connect from a 1st stage on a slung BO cylinder directly to the BOV inlet. I was told that the LP hose attachment to the BOV should only be hand-tightened, so there is no need for any kind of Quick Disconnect fitting there. But, they also have a new dil manifold that has an extra hole in it, so you can get that and a shorter LP hose instead, and connect the BOV directly to the dil manifold.

I am certainly interested in the new rEvo BOV, does it use some sort of quick disconnect to connect the loop hose to the BOV, I like the Shrimp bayonet connections allows easy inspections of the flapper valves. I already feed my Shrimp BOV from the standard rEvo dill manifold, feeding the BOV from the right the LP hose can screw into the end of the rEvo dill manifold where there is a blank port. Is the gas feed on the rEvo BOV able to be swapped from left to right?

 

[rock92]

I do not think it is a rebreather design flaw. I think it is just a scientific fact that the small channels in the EAC leave a lot of area open to never contact the medium when the flow rate through it is increased for a long enough period of time. At least with loose sorb there is never a direct (straight line) for gas to pass and thus the turbulence will increase dwell time and thus contact with medium.

Don't get me wrong, on most dives it was just fine but if we ever had to work hard for several minutes fighting current, flow, etc. then it would bring on the extremely heavy breathing that we learned was time to stop and do something about. Moderation of workload solved this but sometimes stopping in the middle was not really an option. I found that BO before working was easier and then go back to the loop when settled.

I let this creep up on me during my cave course and the hit was borderline of me being able to bailout at all. Obviously I managed or I would not be typing this. I sucked my first AL40 dry in record time and my SAC did not even begin to slow until I was on my next BO tank. I have been very observant of my breathing ever since then.

I built the first loose sorb canister for the Optima, way before DR ever produced theirs, and the difference was night and day in the ability to stay on the loop under a high workload. This is not just my experience but others as well.

Which unit do you dive now?

 

[Dsix36]

Which unit do you dive now?

I went to the rEvo, Defender for 10 months, and now back to my rEvo again.

 

[Dr Simon Mitchell]

Hello,

I know this is off topic, but it came up in this thread. If the mods want to move it I am fine with that.

In isolation, when tested the 2.2kg Micropore EAC is more efficient that the same weight of granular absorbent, by quite some margin.

Often claimed but some perspective is provided by (to my knowledge) the only independent peer reviewed study published in the scientific literature (4 days ago) [1]:

Performance of cartridge and granular carbon dioxide absorbents in a closed-circuit diving rebreather. - PubMed - NCBI

The EAC is more efficient than a granular canister of the same weight by a margin that varies from 0% to 20% depending on the exercise simulation protocol and CO2 breakthrough end point chosen. Whether 0 - 20% difference represents "quite some margin" is in the eye of the beholder, but it is certainly not the "outlasts a granular system by two times or more" that has previously been claimed.

To get comparable scrubber duration results you need to have at least 2.6kg of good diving grade absorbent.

A 2.6 kg scrubber out-performs a EAC. The average duration of an EAC ventilated at surface pressure in a protocol simulating 6 MET of exercise in our experiments was 158 minutes (EAC in an Optima rebreather), whereas a 2.64 kg scrubber (in an Inspiration EVP) lasted on average 202 minutes.

This is independent of the safety benefits of a truly flood recoverable system, with minimal caustic cocktail risk...

I'm not entirely sure what Brad means by "minimal caustic cocktail risk" but we found no significant difference in the pH of water eluted from either granular sorb or an EAC after a 5 minute flood (12.7 vs 12.8 respectively).

You also have a considerably extended breakthrough period from 0.5 to 2% SEV on an EAC than granular sorb; which is a small and very unappreciated design quirk.

Possibly under-appreciated because it doesn't exist? We actually found the opposite. On a continuous 6 MET simulated exercise protocol the two scrubbers exhibited almost identical breakthrough kinetics, whereas on a staged exercise protocol (6 MET for half of the expected scrubber life then 2 MET until breakthrough to either 0.5 or 1 kPa inspired CO2) the granular cartridge exhibited a more gradual breakthrough. This was the reason for a duration difference between the two canisters on this protocol where a breakthrough endpoint of 0.5 kPa inspired CO2 was chosen. Because the granular sorb broke through more gradually, it reached 0.5 kPa inspired CO2 more quickly than the EAC whereas the two scrubbers reached 1.0 kPa inspired CO2 at identical times (on average).

Brad will no doubt claim that these results are confounded by the testing of the EAC in a "poorly designed rebreather". Whether this is true or not, and whether the poor design features somehow selectively disadvantage the EAC and not the granular cartridge remain to be seen (I would certainly not take his word for it). But if so, such sensitivity to rebreather design could, of itself, be interpreted as a disadvantage for the EAC. Perhaps more importantly, unlike Deeplife's flagship "iCCR" (deposits taken 10 years ago, still not released) the Optima is a real rebreather being used by real divers. Thus the comparison of its CO2 scrubbing modalities is of real world relevance.

I would like to be clear that neither I nor my team are in any way "anti-EAC". Indeed, it is a very good product, and it works well. What we are "anti" is misleading claims. There have been many claims made around EACs which we wished to investigate, and as a step in this direction we conducted a comparison with granular sorb in a setting that we considered ecologically valid and fair - a rebreather manufactured to take either.

Simon M

Reference:
1. Gant N, van Waart H, Ashworth ET, Mesley P, Mitchell SJ. Performance of cartridge and granular carbon dioxide absorbents in a closed-circuit diving rebreather. Diving Hyperb Med. 2019;49(4):298-303.

 

[silent running]

Hello,

I know this is off topic, but it came up in this thread. If the mods want to move it I am fine with that.



Often claimed but some perspective is provided by (to my knowledge) the only independent peer reviewed study published in the scientific literature (4 days ago) [1]:

Performance of cartridge and granular carbon dioxide absorbents in a closed-circuit diving rebreather. - PubMed - NCBI

The EAC is more efficient than a granular canister of the same weight by a margin that varies from 0% to 20% depending on the exercise simulation protocol and CO2 breakthrough end point chosen. Whether 0 - 20% difference represents "quite some margin" is in the eye of the beholder, but it is certainly not the "outlasts a granular system by two times or more" that has previously been claimed.



A 2.6 kg scrubber out-performs a EAC. The average duration of an EAC ventilated at surface pressure in a protocol simulating 6 MET of exercise in our experiments was 158 minutes (EAC in an Optima rebreather), whereas a 2.64 kg scrubber (in an Inspiration EVP) lasted on average 202 minutes.



I'm not entirely sure what Brad means by "minimal caustic cocktail risk" but we found no significant difference in the pH of water eluted from either granular sorb or an EAC after a 5 minute flood (12.7 vs 12.8 respectively).



Possibly under-appreciated because it doesn't exist? We actually found the opposite. On a continuous 6 MET simulated exercise protocol the two scrubbers exhibited almost identical breakthrough kinetics, whereas on a staged exercise protocol (6 MET for half of the expected scrubber life then 2 MET until breakthrough to either 0.5 or 1 kPa inspired CO2) the granular cartridge exhibited a more gradual breakthrough. This was the reason for a duration difference between the two canisters on this protocol where a breakthrough endpoint of 0.5 kPa inspired CO2 was chosen. Because the granular sorb broke through more gradually, it reached 0.5 kPa inspired CO2 more quickly than the EAC whereas the two scrubbers reached 1.0 kPa inspired CO2 at identical times (on average).

Brad will no doubt claim that these results are confounded by the testing of the EAC in a "poorly designed rebreather". Whether this is true or not, and whether the poor design features somehow selectively disadvantage the EAC and not the granular cartridge remain to be seen (I would certainly not take his word for it). But if so, such sensitivity to rebreather design could, of itself, be interpreted as a disadvantage for the EAC. Perhaps more importantly, unlike Deeplife's flagship "iCCR" (deposits taken 10 years ago, still not released) the Optima is a real rebreather being used by real divers. Thus the comparison of its CO2 scrubbing modalities is of real world relevance.

I would like to be clear that neither I nor my team are in any way "anti-EAC". Indeed, it is a very good product, and it works well. What we are "anti" is misleading claims. There have been many claims made around EACs which we wished to investigate, and as a step in this direction we conducted a comparison with granular sorb in a setting that we considered ecologically valid and fair - a rebreather manufactured to take either.

Simon M

Reference:
1. Gant N, van Waart H, Ashworth ET, Mesley P, Mitchell SJ. Performance of cartridge and granular carbon dioxide absorbents in a closed-circuit diving rebreather. Diving Hyperb Med. 2019;49(4):298-303.

Hi Simon, thanks very much for posting this, very interesting. How close in volume is the Optima scrubber to the Inspiration? It seems to me that granular sorb properly packed into the same volume occupied by an EAC would have more surface area available for reaction and a slower gas velocity, which would yield increased duration. Is this description correct?

Have you tested differences in breakthrough speed between different granular scrubber designs?

 

[Dr Simon Mitchell]

How close in volume is the Optima scrubber to the Inspiration? It seems to me that granular sorb properly packed into the same volume occupied by an EAC would have more surface area available for reaction and a slower gas velocity, which would yield increased duration. Is this description correct?

Hello silent running.

When the Optima scrubber canister is filled with sofnolime 797 it occupies the same volume as the EAC canister and weighs ~2.1 Kg (about the same weight as the EAC); hence our sense that this was a fair comparison whose results are as described in my previous post. The volume of the Inspo canister is obviously greater, and hence it holds more sorb; about 2.6 Kg which Brad often quotes as being the amount required to be equivalent in absorptive performance to an EAC. Based on our experiments I don't find his claim credible; 2.6 Kg of sofnolime outperforms the EAC (durations to a breakthrough to 1 kPa inspired CO2 quoted in my previous post). He will base his rebuttal of this on an unproven hypothesis that the design of the Optima selectively disadvantages the EAC in some way. You will have to judge the merit of that for yourself. Unfortunately it is not possible to test an EAC against a greater mass of sofnolime in the same rebreather.

Have you tested differences in breakthrough speed between different granular scrubber designs?

No. That's on the list!

Simon

 

[rjack321]

Have you tested differences in breakthrough speed between different granular scrubber designs?

No. That's on the list!

So the identical mass of sorb in a radial vs an axial scrubber? Is there a particular scrubber reaction model you are trying to validate? I actually don't know if (eg) scrubber bed depth to area is at all standardized across various brands and models or not.​

 

[silent running]

Hello silent running.

When the Optima scrubber canister is filled with sofnolime 797 it occupies the same volume as the EAC canister and weighs ~2.1 Kg (about the same weight as the EAC); hence our sense that this was a fair comparison whose results are as described in my previous post. The volume of the Inspo canister is obviously greater, and hence it holds more sorb; about 2.6 Kg which Brad often quotes as being the amount required to be equivalent in absorptive performance to an EAC. Based on our experiments I don't find his claim credible; 2.6 Kg of sofnolime outperforms the EAC (durations to a breakthrough to 1 kPa inspired CO2 quoted in my previous post). He will base his rebuttal of this on an unproven hypothesis that the design of the Optima selectively disadvantages the EAC in some way. You will have to judge the merit of that for yourself. Unfortunately it is not possible to test an EAC against a greater mass of sofnolime in the same rebreather.



No. That's on the list!

Simon

Thanks for all the info Simon, looking forward to more scrubber testing!

 

[Dr Simon Mitchell]

So the identical mass of sorb in a radial vs an axial scrubber? Is there a particular scrubber reaction model you are trying to validate? I actually don't know if (eg) scrubber bed depth to area is at all standardized across various brands and models or not.

Hello rjack,

Yes, that's the sort of thing we would like to look at. We try to pick stuff that is debated in the community (eg here on scubaboard) and bring some objectivity to the discussion with real data.

Here are some other examples from our work in 2019:

Are hypoxia training experiences likely to be safe and of benefit to rebreather divers?

The utility and safety of hypoxia experiences for rebreather divers. - PubMed - NCBI

Do temp sticks in rebreather scrubbers accurately predict CO2 breakthrough?

The performance of 'temperature stick' carbon dioxide absorbent monitors in diving rebreathers. - PubMed - NCBI

Does diving damage your hearing like everyone thinks it does?

The impact of diving on hearing: a 10-25 year audit of New Zealand professional divers. - PubMed - NCBI

The full papers are currently embargoed (for a year) but will later appear on pubmed central. Divers who want immediate access to papers like these in DHM Journal can join SPUMS as associate members.

I should acknowledge the help we get from the community with volunteer subjects (eg the hypoxia study) or from industry (for example Lamar Hires [Diverite] and Martin Parker [APD] loaned us optima and inspo rebreathers respectively for our experiments, and Lynn and Bruce Partridge from Shearwater have provided grants to facilitate studies that have nothing to do with their products).

Simon M