liberty rebreather scrubber time.

[Tassi Devil Diver]

I have left partially used sorb sealed in a canister (rEvo) for over two months and have no worries in using it. I have three sets of canisters for my rEvo, some with varying degrees of usage, a pair of fresh canisters for a deeper 60+m dive, then partially used canisters for shallower dives, with anywhere from 1-3hrs of dive time remaining according to the RMS.

 

[PfcAJ]

I don’t have an issue with storing lightly used sorb for reuse. For me sorb is cheap since I buy in bulk and I dive with my wife. If I choose to store her sorb and she takes a hit and dies I couldn’t live with myself. So I just choose not to reuse it since in the grand scheme of things peace of mind is worth more than the $10 of sorb I saved.

Dont dump the sorb out and repack though. Bad news bears.

 

[tmassey]

Dont dump the sorb out and repack though. Bad news bears.

For us non-rebreather divers, can you give us the brief reason why? I know that carefully packing is always an issue, but how does partially used sorb change this?

 

[broncobowsher]

Sorb doesn't filter uniformly. There is a boundary line as it reacts. Think of a cigarette burning, but never knock the ash off. You start with a new cigarette, as it burns there is a reaction front. Take a half burned cigarette apart and mix the fresh tabacco with the ash. Not going to be good.

Highly over simplified. Take a square block of sorb. use some. Take the block out, turn (not rotate) 90°, put back in. Now the used sorb is an open channel for the CO2 to bypass the active sorb.

The reality of it is not so clear. But if you get a channel of used sorb, you have a bypass channel in the scrubber. A channeled scrubber is useless.

The rEvo has a nice party trick with the twin sequential scrubbers. It lets you run the first scrubber up. Or at least a lot closer to the final usable bit than would normally be acceptable. If you do get to the point of exhausting the first scrubber, the second is still good. Now the scrubbers are half the size, but you get twice as many. The trick is you can use up the first scrubber (or close to it) and take it out. You move the second scrubber up to the first slot and use it. The first gets repacked and goes in the second spot. For the most part you are only dumping half the scrubber material at a time, and have lots of good scrubber material to use.

One of the old horror stories about sorb from the old timers is to just scrape the clumps out, those are the parts that have been used. Add more fresh and go. Trouble is the clumping isn't a guarantee that it is the used sorb. Used sorb can still be granular. The clumps break up back into granules very easy. And used granules look exactly like new granules. Most of these people are no longer around, they are the ones that gave rebreathers a bad image as a death machine. Wasn't the machines fault that the user wasn't following proper sorb protocol.

 

[tmassey]

I figured it would be something like this. So it has more to do with the uncertainty of repacking a mixture of good and bad sorb than it does to do with the amount of good or bad sorb. I’m just surprised that there is such an elevated danger in the mixed situation. But seeing as packing the scrubber is the single biggest risk, I guess making that job noticeably harder/riskier is probably an obvious thing to avoid!

The knee-jerk reaction from a open circuit diver is: if you spent that much, and can’t afford to dump sorb, something’s wrong. It seems to be about $25 to reload a 6-pound canister. But I know I’ve done dives on partially used tanks (there’s still 2000 PSI!) because I was too cheap to get a fill and then regretted not having more gas...

Anyway, thanks for the background.

 

[tbone1004]

@tmassey correct, nothing about quantity of good vs bad, it's about where it is. You need that solid front to actually clean the sorb and "Dead" sorb is basically the same as "no" sorb and that will be instant CO2 hit. The reaction front moves pretty uniformly and you need to maintain that. Mixing=near instant death.

You do need to keep track of stack time though and it's a conscious decision on when to repack or not. I'm actually making a change in my scrubber to hold 4lbs of sorb instead of 6 since the 6lb is a weird time for my cave dives

 

[rjack321]

my general rule is no issue if saving for next day or next weekend. Anything after that and I dump and replace. Can't have you offing C over $10 of sorb!

you must have a tiny scubber or getting better prices than me. We do group buys of a pallet out here and it usually comes out around $125 keg. For a 6lb scrubber that's $18/fill. Retail at $165 keg ends up around $22 fill.

 

[tbone1004]

you must have a tiny scubber or getting better prices than me. We do group buys of a pallet out here and it usually comes out around $125 keg. For a 6lb scrubber that's $18/fill. Retail at $165 keg ends up around $22 fill.

The $10 is the 2ish lbs that hasn't been used in the scrubber, not the whole scrubber

 

[davehicks]

@tmassey correct, nothing about quantity of good vs bad, it's about where it is. You need that solid front to actually clean the sorb and "Dead" sorb is basically the same as "no" sorb and that will be instant CO2 hit. The reaction front moves pretty uniformly and you need to maintain that. Mixing=near instant death.

You do need to keep track of stack time though and it's a conscious decision on when to repack or not. I'm actually making a change in my scrubber to hold 4lbs of sorb instead of 6 since the 6lb is a weird time for my cave dives

That seems just a bit overly dramatic. Yes, it is bad to unpack and repack sorb. Never ever do that! But's it's not instant death either. A CO2 hit can be dangerous but it's not like hypoxia where you just pass out. It could trigger a cascade leading to panic, but it can also be recovered safely.

I've had a CO2 hit before. My experience was that I did one dive on fresh packed sorb, then drove several hours to another location and did another dive the next day. In the first 10 minutes of that dive I started to get very irritable and frustrated over nothing. Then I started breathing faster. I quickly realized my loop was bad and bailed out. On OC bailout stayed put for a few minutes and got my composure back. I did a safe ascent with my buddy and all was well.

I suspect that some channeling occurred in my scrubber during the drive which allowed for a breakthrough. This was on a Sport Kiss about 10 years ago. That unit's scrubber does not have a spring loaded cap holding the scrubber in place and it's a single chamber canister. I have since moved to a Kiss Spirit with two canisters with a simple cylinder shape and tight spring loaded heads. A much better design.

 

[tbone1004]

@davehicks I suspect channeling from travel would be a lot less bad than a mixed scrubber which would be nearly as bad as not having one. That was probably a bit over dramatic though