Question Running a rebreather on only dilluent

[Wibble]

How do divers manage Boyancy with these units?

With constant gas injection the loop would become more and more boyant until you dump gas and suddenly become negative?

And that is the right question. CCR and SCR are very different to open circuit and take quite a lot of time to master.

Can only give you my experience which I reckon on it took me over 200 hours to feel comfortable with a CCR on deco ascents in the sea especially at 6m/20ft without holding on to anything. You need to know the unit and predict what will be happening in the near future. On SCR this means controlling the loop as it dumps out of an over pressure valve.

 

[nadwidny]

And possibly like 5+% enriched argon and whatever else gets stuck on the "oxygen" side of the membrane on a ~5:1 enrichment ratio (CO2, CO, VOC, ...)

Possible vs reality. I've done analysis on membrane generated O2. None those values have ever broken standards for Medical O2 here in Canada. I don't even remember them showing up in any appreciable numbers in the samples I've done.

 

[justinthedeeps]

Possible vs reality. I've done analysis on membrane generated O2. None those values have ever broken standards for Medical O2 here in Canada. I don't even remember them showing up in any appreciable numbers in the samples I've done.

Haven't measured it myself, have heard accounts of higher argon in some membrane or pressure swing systems though. Unless it was actually welding blends misused for diving

Does argon escape through the membrane just as well as nitrogen does? Or does it depend on membrane type? Any multi-membrane systems?

How about CO or CO2? There is more than just oxygen and nitrogen in the atmospheric input.

 

[rjack321]

Lots of good discussion here. I tend to agree teaching SCR mode in an entry level/no deco/no overhead situation unnecessarily complicates things because bailing out to Open Circuit is the best, quickest and safest option.

Being able to use SCR mode in a cave environment is critical and must be taught and the student must master this skill.

I dive double LP85s in the cave. Tanks are generally filled to around 3500 psi which is about 220 cubic feet of gas. (35*6.4) If I switch to SCR mode and use a four-breath cycle while diving SCR mode I turn those 220 cubic feet into 880 cubic feet, essentially a "Gas Extender".

Except it doesn't help you at all if the unit if flooded or you have a co2 hit. So it's not like SCR let's you somehow bring less BO.

Once again, there are virtually zero recorded "near misses" that SCR mode somehow kept from being a fatality. In a cave or otherwise. If someone knows a report of this, let's see it.