liberty rebreather scrubber time.

[rjack321]

When you guys say "channeling" I pictured a gap or area of no sorb that gas would easily pass thru verses the sorb. Is channeling also a path of used up sorb?

If gas is passing from outer to inner area, is it somewhat of a used up area of sorb on the outer surface that gradually moves inward as the sorb is used?

The used up portion is not intuitively obvious since the reaction front is not a smooth line.
A Look Inside Rebreather Scrubber Canisters, Part 2 | John Clarke Online

On radial scrubbers that is out to in, on axial it is top to bottom. Axial is a lot less likely to channel

The fathom is in to out.

What people seem to forget is that a radial is just a large but thin sheet of sorb. The reason it works is the large area not the bed depth. The axial has lots of bed depth but the reaction front area is small

 

[davehicks]

that I would never do. If the lid comes off the sorb canister the sorb goes in the trash

I keep a chart on the wall of my gear station at home to track fills and hours used on each scrubber.

Most of my local diving is one dive a day, once or twice a week. I will do three dives or three hours (whichever comes first) on each fill and then dump it. In between dives (up to a few weeks) I keep it sealed in the unit. If I've only done one hour and follow up with a two dive day, I will dump the exhale side scrubber and refill it. This approach works well for me.

 

[tbone1004]

I keep a chart on the wall of my gear station at home to track fills and hours used on each scrubber.

Most of my local diving is one dive a day, once or twice a week. I will do three dives or three hours (whichever comes first) on each fill and then dump it. In between dives (up to a few weeks) I keep it sealed in the unit. If I've only done one hour and follow up with a two dive day, I will dump the exhale side scrubber and refill it. This approach works well for me.

something I got from my CCR instructor was to put a piece of tape on the top of the scrubber with date filled and every time you pull the head off to let it dry out, record the stack time. This way it's written on the scrubber itself.

@rjack321 is that the only one that is backwards? I can never remember. Either way the large surface area combined with low bed depth does make them much more prone to packing errors and channeling than an axial scrubber with the price being paid by better work of breathing. I have both, don't have strong opinions about either and it wouldn't be part of my buying decision.

 

[rjack321]

@rjack321 is that the only one that is backwards? I can never remember. Either way the large surface area combined with low bed depth does make them much more prone to packing errors and channeling than an axial scrubber with the price being paid by better work of breathing. I have both, don't have strong opinions about either and it wouldn't be part of my buying decision.

Charlie has said the IN to OUT design was chosen based on testing done on the Topaz. And that it is more efficient that way. I've never seen that testing, what was done, or how it was done.
https://www.fathomdive.com/fathom-ccr/scrubber/
The Topaz was designed in the early 1990s and honestly I suspect there are better scrubber fluid models nowadays that might call the IN to OUT choice into question. Maybe its all good enough and an irrelevant detail. I guess it just bothers me that unverified, unrepeated, unpublished "testing" from 30 years ago is cited as the rationale for something being better.

I have an 8lb radial scrubber for my Meg and its a beast. There is some condensation on the inside of the canister in cold water (on the Meg) and I have always imagined that there's no good reason to put that (water vapor) into the middle of my scrubber - but what do I know.

 

[tbone1004]

Charlie has said the IN to OUT design was chosen based on testing done on the Topaz. And that it is more efficient that way. I've never seen that testing, what was done, or how it was done.
https://www.fathomdive.com/fathom-ccr/scrubber/
The Topaz was designed in the early 1990s and honestly I suspect there are better scrubber fluid models nowadays that might call the IN to OUT choice into question. Maybe its all good enough and an irrelevant detail. I guess it just bothers me that unverified, unrepeated, unpublished "testing" from 30 years ago is cited as the rationale for something being better.

I have an 8lb radial scrubber for my Meg and its a beast. There is some condensation on the inside of the canister in cold water (on the Meg) and I have always imagined that there's no good reason to put that into the middle of my scrubber - but what do I know.

I'm not entirely sure I'd want that argument either, and since the unit is just a manual Meg, I would have left the flow the same as the Meg as an extra layer of CYOA, but whatever.

Condensation may actually be worse or at the very least the same with outside-in flow. If you think about it, you exhale gas at ~100f/100% relative humidity. That gas is cooled significantly as it goes through the loop and lung and is knocking water out as it goes. The reaction is not only exothermic, but also generates water, so when the gas goes out of the sorb bed, it's quite hot and will then come in contact with the canister where it will get knocked out anyway. With outside in, that is sucked straight out of the scrubber and into the inhale lung instead of being able to dwell in the canister for a bit since there is more dead space in there.

Inside out does make a bit more sense for potential efficiency improvements, but I'd have to read the study to figure out how much I'd really buy into it, but more importantly the specific efficiency improvement would be unit specific and since CO2 generation is so volatile I'm not sure I'd use it in any "rule of thumb" for scrubber duration.

 

[broncobowsher]

When you guys say "channeling" I pictured a gap or area of no sorb that gas would easily pass thru verses the sorb. Is channeling also a path of used up sorb?

Yes. If there is a flow path through used sorb, that is a channel for the CO2 to pass through. Not as visually clear as a physical void but functionally the same. That is where used sorb gets evil. If you get a streak of used, you have a hole. And it can be even more evil if there is a little good sorb in front. You can start the dive with a working scrubber but when you use up the good part and access that streak of used sorb life goes to ****.

 

[Heat Miser]

It was unremarkable. I had dropped to maybe 60' when I had the issue. I surfaced on 21% OC from my 40cf bailout. I don't typically dive below 100' or plan on deco. I stayed there for a few minutes recovered off the loop and went to the surface. I don't recall any issues or recovery needed at the surface. I changed my scrubber and did a couple more dives that day.

Sounds like you were well educated and understood the symptoms early, I hope it never happens to me, but it appears to be a good lesson in awareness.

 

[Zebra 1]

I'm having minor surgery on Monday, when they put me under at the last second I'm going to pretend to rotate the BOV.
I'll let you know how the rest of the dive goes

 

[broncobowsher]

I'm having minor surgery on Monday, when they put me under at the last second I'm going to pretend to rotate the BOV.
I'll let you know how the rest of the dive goes

Lever or knob?

 

[Zebra 1]

Lever or knob?

Dive Soft lever with ADV & MAV's. Comes stock on the O2ptima now.