Importance of CO2 and scrubber life sensors

[LFMarm]

How important are a CO2 sensor and a scrubber life sensor?

Very few units offer them and although they seem to be both great ideas to monitor the status of the CCR, I understand that the technology is not really mature, despite significant investments from the US Navy over the past couple of decades.

 

[tbone1004]

CO2 sensor I don't put any real merit in. It is basically a go-no-go type of sensor to detect breakthrough but the sensor technology gets very confused with high humidity environments and no one in the industry is really motivated to solve it since the CCR market is so small. CO2 issues you have to worry about occur inside of your lungs and are not necessarily related to expired CO2 percentages.

Temp-sticks are nifty and that is one of the few things that I like about the APD units when I dive them but nifty is the key word. The stack timers on the controllers are good enough and you should know roughly how much time you have on the scrubber. They won't detect channeling or break through and unless you are doing some seriously extreme diving you shouldn't be pushing the duration limits anyway.

Priority of innovation really needs to be on the O2 sensors and the other sensors out there are not ones that I would prioritize in your purchasing decision.

 

[broncobowsher]

Not that important.

Mostly novelty items. As mentioned, CO2 sensors that exist are not happy with humid environments inside a rebreather. By the time they trigger, its too late.

Scrubber, bit more functional. What I don't like is seeing someone use it for the sake of trying to squeeze one more dive out of a fill of sorb.

 

[davehicks]

The best tool for scrubber life is a clock. Just keep track of hour many hours of run time you have on the scrubber. Don't exceed the known good capacity of your unit. These sensors just add cost, complexity and reliability failure points to a CCR.

 

[GF99/99]

The best tool for scrubber life is a clock. Just keep track of hour many hours of run time you have on the scrubber. Don't exceed the known good capacity of your unit. These sensors just add cost, complexity and reliability failure points to a CCR.

@davehicks is spot on!!

And the key is to no exceed the manufactures/your instructors given safe scrubber duration. Yes its a conservative number but there is a actual science behind the number your manufactures provides and it keeps you safe, alive, and able enjoy diving for a lifetime. Just because your buddy does a couple more hours past the manufactures rating does not mean you should or because you read on a post that someone did a 5hr dive on a 3hr rated scrubber.

In the grand scheme of things scrubber is cheap. If you can afford a rebreather, all the training, flights and hotel for diving holidays, etc. then you can afford some scrubber. For example looks like the going rate for sofnolime in the US is $168 shipped from SubGravity. I will just use a JJ scrubber for example. It is 2.3kg and rated by JJ for 3hr or use. So that is $19.32 to get a 2.3kg 3hr fill or $6.44 per hour. So for every 1hr you push you scrubber over you are only saving your self $6.44 so ask your self is your life really worth saving $6.44/hr

If you just stick to the clock then there is no need for fancy CO2 monitors.

 

[LFMarm]

Thanks all for the answers. My question was not to look for ways to save on scrubber but rather have longer single dives. From my calculations the limiting factor for me will be the scrubber and not the O2, hence the question.

 

[AJ]

Thanks all for the answers. My question was not to look for ways to save on scrubber but rather have longer single dives. From my calculations the limiting factor for me will be the scrubber and not the O2, hence the question.

If so, buy a bigger scrubber. Mine does 3 hours according to the manufacturer on the standard scrubber. I'am done after diving for 3 hours to be honest.

 

[GF99/99]

Thanks all for the answers. My question was not to look for ways to save on scrubber but rather have longer single dives. From my calculations the limiting factor for me will be the scrubber and not the O2, hence the question.

O2 is usually never the limiting factor nor is scrubber its usually bailout. If your doing 3hr+ run times it usually means you are going really deep or really far penetration so a dive like this will require a lot of bail out

If so, buy a bigger scrubber. Mine does 3 hours according to the manufacturer on the standard scrubber. I'am done after diving for 3 hours to be honest.

Spot on. For the average diver a 3hr dive is more than plenty hence why most units come standard with a scrubber size in this 3-4hr range. And if you are doing bigger dives that is why some manufactures offer optional larger scrubbers for those that require it. I think the largest I know of is Fathom's monster 5.7kg radial followed by JJ's 4 kg radial, then XCCR & Meg's 3.6 radial. But your talking about a very very small percentage of the CCR diving community that actually requires scrubber durations like this. I would venture to say that for 99% of the CC divining community a standard 3-4hr scrubber is plenty.

 

[broncobowsher]

Some rebreathers have larger scrubbers as an option. Revo had a redial flow scrubber kit that added hours of capacity. Never seen one in person. Not even sure if they still make it.

I have done a 3½ dive in Truk. Actually turned into less diving for that day compared to the normal 2 shorter dives. It was nice warm water as well. And those are about as perfect conditions as you can ask for. The 2½-3 hour dive is about perfect. Your CNS clock is getting up there as well. Few hours on the surface and take a second dive that day. You will get more time in the water over a longer singe dive.

What kind of dive are you planning that will be 3+ hours at a time?

 

[LFMarm]

What kind of dive are you planning that will be 3+ hours at a time?

Long wreck dives at normoxic depths. With 2xAL80 the bottleneck will be the scrubber, then the oxygen and finally the bailout.