Half-packing sorb -- Possible, or deadly?

[Capt Jim Wyatt]

You _could_ partially pack an axial scrubber,

When you turn upside down the sorb will fall from the bottom of the scrubber to the top. Loose sorb like that is equivalent to no sorb at all.

 

[OTF]

I hate to be that guy on the internet attacking the premise without answering the question, but what's the issue with storing one packed scrubber for use over a couple of short dives? Why would it be so "impractical" to leave it sealed in the unit or a labeled drybag?

 

[ahereng]

My meg had various spacers for different scrubber volumes. I don't think that still exists as you could use the wrong spacer and leave an air gap that would bypass the scrubber entirely.
I believe the consensus was, while nice to have, not worth the risk to save $20.

It still exists Scrubber Support - InnerSpace Systems Corporation

 

[Pavao]

When you turn upside down the sorb will fall from the bottom of the scrubber to the top. Loose sorb like that is equivalent to no sorb at all.

Design dependent I think, the SF2 has a scrubber you can pack “any” amount you want. To be clear, not saying that’s how it’s intended, I’m saying it has no fine line to pack sorb to, too little and channels form, too much and won’t close lid type. It has a lid held down by a strong spring screwed down by a wing nut, so tolerance in sorb amount variance is quite high I think.

 

[Pavao]

Fathom has 2 sizes, 3 really, but the third one requires a larger can, so only one size would fit with a spacer, but I guess it’s possible one could end up with the shorter scrubber and no spacer.

Come to think of it, for the 3+ options on some units, why not manufacture the scrubber with the spacer already built into it as opposed to independent pieces, you can’t use a given size without the appropriate spacer and vice-versa, they’re married to each other anyway? Seems so obvious.

 

[davehicks]

I hate to be that guy on the internet attacking the premise without answering the question, but what's the issue with storing one packed scrubber for use over a couple of short dives? Why would it be so "impractical" to leave it sealed in the unit or a labeled drybag?

There is no issue with this at all. I've done this for 20 years now. Pack the unit fresh, do an hour of diving, rinse the unit and loop, dive it again a week later. Just keep track of the scrubber run time. I use a tracking sheet on the wall of my gear station and my Shearwater stack time.

 

[stretchthepenn]

I hate to be that guy on the internet attacking the premise without answering the question, but what's the issue with storing one packed scrubber for use over a couple of short dives? Why would it be so "impractical" to leave it sealed in the unit or a labeled drybag?

Your question is a good one, but the original question is more theoretical than anything. Odds are that a sealed-up sorb container would stay good/good enough.

But let's assume something like...um...it's wintertime, and our diver is landlocked. He's only able to dive when the local quarry is open, and it's on an erratic winter schedule, so he can only go dive once every two months.

Or perhaps something is going on in the diver's professional or personal life that makes it impossible to dive regularly or predict when his next opportunity to dive will crop up, but he still wants to get wet and keep his RB skills fresh.

Again, it's mostly a theoretical question, but the use case is semi-plausible.

 

[lostsheep]

I believe dwell time in the sorb would be dangerously decreased.

To expand on my $.02; bed length and cross sectional area both have an affect on scrubber behavior, you can not just shorten it. See Clark’s book BREAKTHROUGH.

Breakthrough | John Clarke Online

Revealing the Secrets of Rebreather Scrubber Canisters More than thirty years of research, testing, and computer modeling of rebreathers in a military laboratory have been condensed into a small, approachable monograph. Breakthrough is an affordable textbook unlike any other in the technical...

johnclarkeonline.com

 

[sea_ledford]

Design dependent I think, the SF2 has a scrubber you can pack “any” amount you want. To be clear, not saying that’s how it’s intended, I’m saying it has no fine line to pack sorb to, too little and channels form, too much and won’t close lid type. It has a lid held down by a strong spring screwed down by a wing nut, so tolerance in sorb amount variance is quite high I think.

I seem to remember that the minimum fill depth was around 2/3's of the total volume. That was related to dwell time. Also not sure if that was the intended purpose, but it was really nice to not have to be so precise about filling. I sure do like filing that scrubber vs the radial one in the Prism though! The only thing easier is an ExtendAir cartridge.

I think the only time I remember doing a short fill was if I was going to be doing some shallow water proficiency type diving in the middle of the off season. Saving 1/3 of the sorb volume just wasn't that big of a deal.

 

[211ratsbud]

Fathom has 2 sizes, 3 really, but the third one requires a larger can, so only one size would fit with a spacer, but I guess it’s possible one could end up with the shorter scrubber and no spacer.

Come to think of it, for the 3+ options on some units, why not manufacture the scrubber with the spacer already built into it as opposed to independent pieces, you can’t use a given size without the appropriate spacer and vice-versa, they’re married to each other anyway? Seems so obvious.

Because different head and canister combinations exist on top of different scrubber combinations.