@JohnnyC not a lot of CO2 production when you're using scooters...
797 is something like 150l/kg, so on those SF2 scrubbers, using our normal rule of thumb with an hour a pound you have 5 hours on that scrubber. It is able to theoretically absorb 330liters of CO2, knock off some efficiency, usually 70% for axials which is 230 liters. We usually use 1lpm for calculations of O2 for consumption which we know is high, but call it 230 minutes of burn time.
CO2 production for scrubber duration is calculated at .8lpm, 1.3lpm, and 2.5lpm ish during testing. .8lpm is kind of lazily swimming, 1.3lpm is something like that river dive, and 2.5lpm is basically sprinting and is not considered sustainable. IIRC NEDU uses 1.4lpm for their testing.
1lpm seems pretty conservative for a normal use case with the rebreathers, especially if for deep diving where a majority of the time may be spent on deco essentially not moving and the 1lb/hr is practical for that.
The 2.5kg can theoretically process ~375liters of CO2. Assuming maybe 80% efficiency is 300liters, and over 8 hours is .625lpm CO2 production. If most of it was that calm lake dive and/or dpv/deco type diving I'd say that's easily plausible
Oh I'm aware of the math, but it IS NOT comparable to Intersorb 812 (despite both being 8-12 mesh) or Spherasorb 408. In Simon's Sofnalime vs Spherasorb comparative study, breakthrough occurred 32% faster in the Spherasorb vs Sofnalime. They're doing those dives on blue kegs, not white..... It's certainly not a direct comparison as the Spherasorb is 4-8 mesh and Sofnalime is 8-12, and Intersorb is 8-12 mesh as well.
Translating into real world diving (warm water, lower CO2 production, etc.), I'm sure the difference is not that dramatic under real world operating conditions, but the fact remains that they're doing those dives on demonstrably less efficient scrubber material. The 8-12 mesh products do not produce similar results it would seem, although certainly less difference than 4-8 mesh. And I don't know why anyone would choose to dive 4-8 mesh.
rEvo is certainly comfortable with Intersorb though, so it's not like it doesn't have merit as a useful absorbent.
They're doing those dives without issue so obviously they are successful, but I personally don't want to be that close to the edge. To me it would be like planning bailout requirements on standard OC SAC rates as opposed to a worst-case CO2 hit scenario.
Study abstract for anyone else who wants to take a look: The duration of two carbon dioxide absorbents in a closed-circuit rebreather diving system. - PubMed - NCBI
Again, it's Spherasorb 408 vs. Sofnalime 797, so different manufacturers, different mesh. Keep that in mind.