The misunderstood mCCR explained

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You all are mixing constant moles and variable volume with every other post and trying yourself in knots over it.

Moles is introductory high school chemistry so I think that qualifies as "lay person" language - but perhaps not
 
Thank you for that clear and extensive comparison. I've been collecting data about rebreathers for a while and made my choice a few weeks ago : mCCR. Your work just confirms my choice. I'll be doing my training in July. Be glad to read more of your works.
 
You all are mixing constant moles and variable volume with every other post and trying yourself in knots over it.

Moles is introductory high school chemistry so I think that qualifies as "lay person" language - but perhaps not

moles were basic high school science for me, but you would be surprised how many people have never had any exposure to chemistry in hs or college. My view is skewed because I went to a private high school with much better instructors than most public schools. My wife teaches science at a university and you would be shocked at how many kids got very limited basic science exposure in hs. From what I’m seeing moles is definitely not in most people’s hs science background. Kinda scary.
 
I dove an mccr revo for a couple of years before I dove an HCCR revo for another couple of years.

On both of those units, what was the ip set at @Dsix36 knows. It was a fixed ip. At 20' or 200' it was still pumping out 140psi. No big deal. But at 300', what was the reg pumping out? If I hit the MAV, how long did I hold it down for? Trick question, because it wouldn't add anything at 300' no matter how long I held it.
 
mCCR can have a leaky valve with fixed IP 1st stage. Or a needle or only a manual add valve.

The false statements also caught my attension: "As we descend in the water column, diving physics increases our partial pressure of the oxygen, which means we need to add less oxygen into the loop."

"After all, when your depths approach 100 meters, you need so little oxygen to sustain you."
 
As I've said multiple times, this thread is for the layperson. Someone who is perhaps interested in CCR, but not a CCR diver. So their level of knowledge at a casual informational stage of research isn't required, nor is an in depth technical explanation.

Furthermore, a tech divers doesn't need to know the chemical properties of sorb. They just need to know that it absorbs CO2, how to use it safely not not to get it wet. A tech diver doesn't need to know the amount of chromium in the stainless steel, the exact composition of their batteries, etc.

You're being argumentative for the sake of being argumentative at this point. We get it, you're a really smart guy who knows lots of stuff. You're confusing everyone else. Your english is a bit confusing and that's not helping matters.

This is an article for people to learn a bit more about the the concept of the mCCR, nothing more.

There is a lot of good material in your article, and the illustrations are very nice. However, I'm a little surprised at the pushback. You posted an article in a public forum. Someone pointed out what they saw as a problem with it, and you questioned his motives, made fun of him, accused him of "nitpicking" and ridiculed his grasp of the English language. You used a silly analogy - CCR divers don't control the chemical composition of sorb but they do need to understand how gas flow works, because it's under their direct control.

I don't think that fsardone was deliberately trying to confuse people or attack you personally. He was taking the time to point out an issue with your work. Many authors would welcome that, even if it wasn't a problem with content but the way that something was explained. Your article confused me a bit as well, so just saying that it's for laypeople and that means it doesn't have to be clear or precise isn't reasonable.

I dive an eCCR, I don't know much about mCCRs, but I was also not sure about some of your statements. So while I may be wrong, it would still make sense for you to look at the problems people have understanding the text.

You said "as we go deeper the trickle of oxygen gradually decreases". I was under the impression that the L/min of O2 was constant until you reached the depth limits of the fixed IP first stage system. The upstream pressure isn't changing during a dive (assuming no first stage failure), so the density of O2 is unchanged, so isn't that where CMF comes from? The whole point is that your body uses the same number of molecules of O2 per minute at every depth within the range of the unit, so that's why the CMF delivers the same number of molecules, just below metabolic rate, with manual addition to make up for increased workload or ascent. The fact that after passing the orifice they expand to ambient pressure, and so there will be less volume at deeper depths than at shallower depths (PV=nRT) is irrelevant, but maybe that's what you meant by saying that the trickle gradually decreases? This isn't a question of oversimplifying for a non-technical audience, it seems to imply something different than what is actually happening. This is from Paul Raymaeker's article.

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Also, you said this: "As we descend in the water column, diving physics increases our partial pressure of the oxygen, which means we need to add less oxygen into the loop." Maybe this is another case of confusing volume and mass, but that's an important difference, and it deserves a clear explanation, even if you are writing for an open circuit audience. I thought that the main point of the CMF orifice was that it delivered just under what your body metabolizes at any operational depth, and metabolism is not depth dependent.

fsardone is not the only person in this thread to have some concerns. So instead of ridiculing the person who has gone out of his way to give you feedback, why not look at your text and see if what you are trying to say could be explained more clearly?
 
It is all about gas density. The deeper a diver goes, the denser the gas becomes. The denser a gas becomes means that there are actually more molecules of oxygen in the same volume of gas. This means that the po2 will remain steady for a longer period as the body will still metabolize at the same rate regardless of density. diver can go for longer periods of time without manually injecting to keep po2 up. go deeper, add less; go even deeper and add even less, etc. etc. etc. right up until you hit the threshold of the ip and the flow stops entirely. even at this point the po2 will hold steady for a longer amount of time than most people realize. it is just the ascent that becomes problematic now if you can no longer add oxygen until you get above the ip threshold
 
Serious question. How do you dive deeper than 10 atm. on a mccr? Do you just crank up the IP on your O2 regulator? Is there a practical depth limit for mccr that is less than eccr? I see eccr divers regularly diving to 600 feet, is that even possible with an mccr?
 
Serious question. How do you dive deeper than 10 atm. on a mccr? Do you just crank up the IP on your O2 regulator? Is there a practical depth limit for mccr that is less than eccr? I see eccr divers regularly diving to 600 feet, is that even possible with an mccr?
Very possible to accomplish this task. I just have a small bottle of a rich diluent plugged into my offboard manual add valve that is run by a depth compensating regulator. 50% seems to work pretty good, since pure oxygen makes it extremely easy to overshoot your po2 when adding at those kinds of depth.

on a side note - the use of a needle valve rather than a cmf solves the issue and I just turn up the flow as I need to. this works great on a eccr unit to fly it manually but still have a "parachute" if you get task loaded.
 
on a side note - the use of a needle valve rather than a cmf solves the issue and I just turn up the flow as I need to. this works great on a eccr unit to fly it manually but still have a "parachute" if you get task loaded.
I asked that very question when I was getting into CCR, and was dissuaded. It seemed like the best of both worlds: eCCR as a parachute, and needle valve to minimize MAV pushes. But I was told that I would no longer hear the background click of the solenoid in e mode or as a reminder if flying manually when I got task saturated. And absent that background noise, if my seldom used solenoid failed, I wouldn't be reminded by the silence and would be at greater risk of missed hypoxic change.
Your thoughts?
 
https://www.shearwater.com/products/swift/

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