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.
Which kind of proves the point that you were not getting linear flow with the EAC originally. And therefore using very little of its available capacity.
If you were to do a direct scrubber only duration comparison:
- Optima EAC scrubber
- Apoc EAC scrubber
Connecting from the right angle fittings on the ends of the respective scrubbers.
The EAC is solid state so there can be no variation in the actual media itself or its packing.
And despite that, you will have considerably higher WOB and lower duration with the Optima scrubber. It’s simple physics and gas flow.
The Apoc scrubber has a considerably higher diameter entry/exit bore, engineered flow cones at each end and nothing in the way of the gas flow through the EAC and a few other design tricks.
This doesn’t even consider the rest of the rebreather design differences that further caused your issues as experienced diving an EAC in the Optima.
DeepLife and Divex/JFD have both proven you can quite safely use the EACs at 350m for commercial diving. Which is about as hard a work environment as you can certify a rebreather for.
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.
Don, did you ever think something was wrong and go back to the manufacturer to ask them for their unmanned testing; to prove to yourself that you were diving within the units tested safe operating envelope?
I’ve done a lot of stupid things on the Apoc/Incursion range test diving them. And I’ve yet to get to where the breathing on the unit was excessively hard or I’ve felt I’ve overbreathed the scrubber!
Were you diving it at the time with a gag strap and a BOV to make the switch over easy without the need to open your airway to water ingress?
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.
How much granular sorb did it hold? As before, if you got 2.6kg+ of granular sorb into it, you have exceeded the likely maximum capacity that a single EAC can generate. Hence the dual scrubber EAC models for longer duration work, which are rated for 5hrs in 4’C water down to 100m, at the mouth.
Diverite have had their granular scrubber out for sometime now, what’s its duration compared to the EAC? WOB?
Because the horizontal design of your EAC scrubber didn’t offer any caustic cocktail mitigation and therein flood recovery. And you also removed the risk of hypoxia/hyperoxia from water blocked cells as others experienced. Going to granular could only be a win/win for you and others. But that just shows the importance of manufacturers actually testing these products through the full range of the diving conditions before giving them to human crash test dummies to try before they are certified and offered for sale.
What I meant was that the EAC used in the Optima has a design flaw of having too many voids for high volumes of gas to pass through at high velocity such that it does not bond with the chemical and properly scrub. Lower WOB in this case means less dwell time in the cartridge media, less dwell time = less efficient CO2 absorption, which is a design flaw as compared to granular absorbent, IMHO...
The cause of the early EAC breakthrough on the Optima is that only 2/3rds of the EAC area is used - this is due to the poor flow design and channels being blocked by O2 cells – which causes excessively high WOB by that units scrubber. These issues do not occur on any OSEL rebreather using EACs: as a consequence, there is no early EAC breakthrough and no sudden breakthrough with high RMVs. The OSEL rebreathers have been tested extensively and the full test results published for all to scrutinise. This is not the case for other manufacturers, such as the Diverite, and no comparison should be made. Getting the full performance out of EACs really does depend on correct scrubber design.
Don and others might prefer to throw away .pdfs covering unmanned testing but there is an important reason for them. As this issue highlights.
Seriously, DL’s results of their testing have been openly disclosed for over a decade and if someone wanted to have a go at them, that would be a VERY easy vector to go down. Ever wonder why NO ONE has called DL out for their test results…. There is a reason why DL publish them with full calibration data, method and everything required to very easily enable others to directly compare the results to the performance of other makes of rebreathers.
Just as no one disputes the EN14143 requirement for the need to retain the faceplate to prevent the diver drowning when they go unconscious. Which is why you see some form of gag strap on every rebreather that meets all the CE certification requirements.
