Question What is the smallest theoretical and current scrubber size?

[Tom_Ivan]

I read and see people talking about rebreathers that have many hours of dive time. But what if you wanted a scrubber that was as small as possible and you were happy with a 60 minute max dive? To ensure enough dwell time at the end of the dive, how many KG of sorb would be needed?

Follow up question, what is the smallest canistor on the market and what is the advertised dive time?

 

[justinthedeeps]

I have wondered this also, though honestly, cutting a ~kg off of the scrubber size does not give that much of a weight or size advantage.

If you look at the rEvo canisters for example, they are already fairly compact, and the sorb in them is only a small portion of the overall weight/size of the rig.

A couple constraints and minimums:

1. the effective molecular path of the CO2 through the material must be long enough that it all interacts and is neutralized, before exiting the scrubber(s).
A shorter scrubber might not allow enough time for CO2 to react completely.

2. the breathing resistance must be low enough at 40 L/min to pass minimums for safety (CE, etc).
A narrower scrubber might result in unsafe breathing resistance.

More weight could be shed from a rig using carbon fiber backplate and cylinders, plastic construction (Prism2, KISS), or one of the side/chest mount configs that don't use metal frames.

If the sorb costs for sporadic uses under ~3 hours is the concern, CCR might not be the right sport

But a properly stored canister can be used for multiple dives. While the CE and training standards require a scrubber to work for 180 minutes at 40 L/min gas flow and up to ~2L/min of CO2, countless field results show that most CE 'type T' ~2.3+ kg rebreather scrubbers can go for 6 or more hours under normal (relaxed) diving conditions (< ~1L/min oxygen metabolic rate), spanned over multiple non-challenging dives. [But don't take that as a recommendation!]

 

[rjack321]

I read and see people talking about rebreathers that have many hours of dive time. But what if you wanted a scrubber that was as small as possible and you were happy with a 60 minute max dive? To ensure enough dwell time at the end of the dive, how many KG of sorb would be needed?

Follow up question, what is the smallest canistor on the market and what is the advertised dive time?

It's not really marketable or practical to have a 60min scrubber. The dwell time is so short you'd have some serious depth and temp limitations trying to pair down that far. The drager ray is close to your 60min at 70mins. BUT that was an SCR so there's some venting of CO2 in every cycle. Plus it's depth limited by the supply gas at 22m. People have converted them to mCCR and taken them deeper too. But that's outside of any manufacturer recommendation or testing. But its roughly a 60min scrubber in cold water and 30m depth so it's the closest to answering your curiosity.

https://www.ultimatedivelog.com/articles/13.pdf

Draeger Ray

I have a Ray scrubber in the garage. I don't know exactly how much sorb it holds and the weight isnt reported in the manual. I'd say roughly 1.8kg. The Ray is no longer made or sold because nobody wanted such a thing.

 

[mr_v]

60 min scrubber time is 20 min dive time when you plan by thirds. That's a no for me, dawg.

 

[arkstorm]

Doesn't the Dive Talk Go RB sort of match what the OP is looking for (1.4 kg sorb canister / 2.5 hour duration)?

 

[broncobowsher]

I was thinking the KISS conversion of a Hollis Explorer. I recall it wasn't good because the scrubber was too small. There wasn't a good way to increase the scrubber to a more usable size.

I could see a small scrubber being even more wasteful of sorb. You would be changing it after every dive. You start at 60 minutes, go do a 30 minutes dive and there is no way anyone with any rebreather training would think about heading out with a 30 minute run time left. That is zero reserve. So now you are tossing 50% of your sorb. If you run a 3-hour scrubber and dump with an hour left, you are only tossing 33% good sorb. So making it lighter, you just made it more wasteful. I am sure under just the right thermotical conditions it could be better, but general real world, with realistic reserves, not so.

 

[rjack321]

I was thinking the KISS conversion of a Hollis Explorer. I recall it wasn't good because the scrubber was too small. There wasn't a good way to increase the scrubber to a more usable size.

I could see a small scrubber being even more wasteful of sorb. You would be changing it after every dive. You start at 60 minutes, go do a 30 minutes dive and there is no way anyone with any rebreather training would think about heading out with a 30 minute run time left. That is zero reserve. So now you are tossing 50% of your sorb. If you run a 3-hour scrubber and dump with an hour left, you are only tossing 33% good sorb. So making it lighter, you just made it more wasteful. I am sure under just the right thermotical conditions it could be better, but general real world, with realistic reserves, not so.

Not to mention people have tried to make light "recreational" rebreathers for a long time. The kiss gem, the drager ray, now the "go". Maybe the go will take off but its a lot bigger than a 60min dive unit

To date "small and light with limited time and depth" just doesn't sell

 

[Whitrzac]

There are plenty of custom ones out there for sump diving. I've heard stories of thermos's being used and a pendulum design.

The market is small enough that when you know you need one, you know the people that can make them or have them.

Mike even made a mini sidewinder to fit into smaller caves.

 

[rjack321]

There are plenty of custom ones out there for sump diving. I've heard stories of thermos's being used and a pendulum design.

The market is small enough that when you know you need one, you know the people that can make them or have them.

Mike even made a mini sidewinder to fit into smaller caves.

yeah the Kiss pendulum CCR (predated the sidewinder) was a very limited run, not sold commercially, and was pretty dicey CO2 wise. But the scrubber was down around 1 kg. It would never pass CE or any serious cold water, high O2 consumption test, like instant breakthrough lol

 

[jale]

Small scrubber units here:

Closed Circuit O2 Rebreathers and Training?

Fascinating informative thread! You guys are awesome. I sometimes fantasized about getting or building a pure O2 rebreather for long shallow photography dives, but now I see why nobody seems to do that.

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