Fathom Gemini WOB on partially used scrubber

[lostsheep]

Tipping out the lime into a tray and letting it dry in the window for an hour or two before repacking it in the canister?

Someone who actually dives a Gemini or Sidewinder needs to chime in on this.


ETA: this is one of those things that should have been addressed by your instructor. I’m not gonna ask who your instructor was but the field isn’t exactly big and you asking this question is concerning.

 

[flymolo]

Tipping out the lime into a tray and letting it dry in the window for an hour or two before repacking it in the canister?

no never repack partially used scrubber

 

[Mobulai]

Is it worth removing the offending scrubber after a dive, and leaving it to stand in my apartment for a day or two to let it dry? Putting it in a sealed container with silica gel, in an attempt to draw out the moisture? Tipping out the lime into a tray and letting it dry in the window for an hour or two before repacking it in the canister?

When I did my class for sidewinder in Egypt my instructor, and later on a buddy of mine (recently also a mod1 instructor) just left the canister open in the sun to let them dry/air out as much as possible (edit: just like David mentioned below), we only reused one side after short dives (less than an hour), and packed new sorb every 2nd dive max— that’s the limit of my experience (I got like 20hrs only)
With a Gemini probably easier as you can unpack the inner canister and take the unit itself for a clean
YMMV

 

[JCM@Atlam]

When I did my class for sidewinder in Egypt my instructor, and later on a buddy of mine (recently also a mod1 instructor) just left the canister open in the sun to let them dry/air out as much as possible, we only reused one side after short dives, and packed new sorb every 2nd dive max— that’s the limit of my experience (I got like 20hrs only)
With a Gemini probably easier as you can unpack the inner canister and take the unit itself for a clean
YMMV

I think the Gemini takes more lime? 4.4kg (9.7lb) in total. That's good for duration but bad for wastage when my runtime is normally ~90 mins

 

[davehicks]

I posted on this topic in another recent thread. I dive 3 hours on a Kiss Spirit, often 1 hour a day on three days, then swap inhale and exhale canisters refilling the inhale. I don't notice any work of breathing issues.

My canisters are stored vertically between dives and any excess water can drain in the counter lungs. I don't think they are typically wet however. I often remove the loop hoses to sanitize and dry, leaving the canisters open to air for a day or two.

After 3 hours of diving i rarely see more than a quarter cup of water in the lungs.

Post in thread 'Half-packing sorb -- Possible, or deadly?'

Mar 11, 2025

Expanding on this, someone could only fill 1 canister of the sidewinder and do a 3hr dive no? or rotate exhale to inhale side and get 9hrs from 1.5 fills!

I dive the kiss spirit, the back mount predecessor of the sidewinder. It has two separate sorb canisters, inhale and exhale side. The Exhale side gets used first, and after 3 hours of diving the Inhale side is typically still 90% unused.

So Yes, you can rotate the Fully Filled canisters. My typical pattern is to do three hours of diving, dump the exhale side and refill. Rotate Inhale to Exhale, put the fresh canister on the...

• davehicks

• 

 

[Mobulai]

I think the Gemini takes more lime? 4.4kg (9.7lb) in total. That's good for duration but bad for wastage when my runtime is normally ~90 mins

Yes 4.4 is far more than a standard SW canister can take
For the ~2.8 the SW can take, we estimated (in warm water) 3.5hrs stack time
Doing 2 90min dives on that leaves just a tiny buffer as a margin of safety

In your case I’d do the „revo“ approach, but air out the internal basket to lose some of the trapped humidity

 

[JCM@Atlam]

Yes 4.4 is far more than a standard SW canister can take
For the ~2.8 the SW can take, we estimated (in warm water) 3.5hrs stack time
Doing 2 90min dives on that leaves just a tiny buffer as a margin of safety

In your case I’d do the „revo“ approach, but air out the internal basket to lose some of the trapped humidity

I just wonder how effective it would be, given the canisters on the Gemini are relatively long and narrow. Loathe to leave them in sunlight as it would probably damage the o-ring on the canisters

 

[JCM@Atlam]

I posted on this topic in another recent thread. I dive 3 hours on a Kiss Spirit, often 1 hour a day on three days, then swap inhale and exhale canisters refilling the inhale. I don't notice any work of breathing issues.

My canisters are stored vertically between dives and any excess water can drain in the counter lungs. I don't think they are typically wet however. I often remove the loop hoses to sanitize and dry, leaving the canisters open to air for a day or two.

After 3 hours of diving i rarely see more than a quarter cup of water in the lungs.

Post in thread 'Half-packing sorb -- Possible, or deadly?'

Mar 11, 2025

Expanding on this, someone could only fill 1 canister of the sidewinder and do a 3hr dive no? or rotate exhale to inhale side and get 9hrs from 1.5 fills!

I dive the kiss spirit, the back mount predecessor of the sidewinder. It has two separate sorb canisters, inhale and exhale side. The Exhale side gets used first, and after 3 hours of diving the Inhale side is typically still 90% unused.

So Yes, you can rotate the Fully Filled canisters. My typical pattern is to do three hours of diving, dump the exhale side and refill. Rotate Inhale to Exhale, put the fresh canister on the...

• davehicks

• 

I do wonder if mine has a little leak in the exhale hose. I got a cut in the end of it a while back, so cut it shorter and reattached with cable ties. Certainly passes a bubble check but maybe a little water creeps in. I have a new hose on order

 

[macado]

I do not own a Gemini but I believe the scrubber size referenced above is not accurate.
The Gemini holds a total of 4.8 lb (2.2 kg) of sorb. Each scrubber is 2.4lbs / 1.1kg.

Someone feel free to correct me if this is not accurate.

I dive a Sidewinder/Gemini-type clone so I'm just giving you my own personal experience. For me - I will typically either rotate scrubbers (move inhale canister to exhale side and repack exhale side). I'm also comfortable going a bit longer without repacking but I also have a water trap in mine that keeps a lot of the lung butter (excess moisture) out of the exhale side. I also only use 2 dust filters on the top. I think 4 is overkill, at least for my particular rebreather.

If your typical dive is only ~90 minutes then you could get away with dumping the exhale cartridge, move inhale to exhale and repack the other scrubber if you wanted to be very conservative. You'd only have to pack 1.1kg of sorb.

If it were me I'd would also leave the scrubber out to dry for a bit. Actual scientific evidence (not people's feelings) shows that leaving a scrubber unsealed for a day or so will not negatively affect the CO2 removal capacity. If you're diving the next day simply leave it on the counter. I will usually leave the scrubber on my work bench overnight. If I'm not diving until next weekend then I'll put it in a sealed dry bag the next day.

See paper here: Storage of partly used closed-circuit rebreather carbon dioxide absorbent canisters - PMC

Another option. I'm saying this with a bit of a disclaimer as I don't own a Gemini and this is probably not recommended. One thing you could do if WOB is an issue is pack with 4-8 mesh. I'm saying this with the caveat that that this sorb is probably NOT approved for the Gemini and it will have less duration than typical 8-12 mesh. People can make their own adult decisions about what they consider safe but I know plenty of people who use 4-8 mesh in their Sidewinders.

 

[davehicks]

I do wonder if mine has a little leak in the exhale hose. I got a cut in the end of it a while back, so cut it shorter and reattached with cable ties. Certainly passes a bubble check but maybe a little water creeps in. I have a new hose on order

Check your mouthpiece as well. I've had leaks from a tear on a mouthpiece and it does not show up in any pos/neg check.

Finally, I don't use scrims or filters at all. These could impact WOB. I don't have any issues with dust in the unit. The Kiss has a tight metal mesh on top of the canister, and I find that sufficient. I might have used a filter a few times when I first started CCR almost 20 years ago, and quickly found them to be superfluous. Other CCR units and design might require them, but not the Kiss Spirit. I think in ages past some Sorb formulations were a lot dustier than Molecular Sofnolime, which has very little.