Thank you, Ken!
On the END limit, my calculation for using 20% Helium is 132' would give me an END of 100' (treating O2 as narcotic also). So, with Helitrox Dil CCR, I could dive to the limits of normal recreational diving. Treating only N2 as narcotic, the END limit would allow me to go even deeper. Am I missing something? What I would LIKE to be able to do is dive to normal rec limits (130') and, eventually, do some deco on dives to that limit, before I have to step up to the full mixed gas training. I was thinking Helitrox Dil CCR would let me do that.
I have learned enough about CCRs over the last year that I actually understand your paragraph about the solenoid versus leaky valve.
But, for some reason I had the impression that you can get a rEvo configured as an actual eCCR. Is that not true?
I am only waiting on an email back from Best Publishing to clarify the offerings on their website and I will be ordering Bozanic's book.
I consider O2 as narcotic as N2 and the way I do END calcs is based on the fraction of O2+N2 in the mixture. 25/20 at 150' = 113'.
OK, let's talk Revo's and solenoids for a second.
Here's the Revo manual.
http://www.revo-rebreathers.com/wp-content/uploads/2016/02/Manual_rEvo_III_CE_2014_v05_ENG.pdf
My understanding is when you buy a Revo with the setpoint controller (solenoid) you still get the leaky valve with the unit, hence it has both and we call it a Hybrid. Personally, I'm not a fan of hybrids and if I were to buy a Revo, I would probably buy the mCCR model.
An mCCR makes sense -- it's a safe and simple system that forces you to develop good/safe habits. Failure to properly monitor and maintain your PO2 leads to hypoxia and death -- that's a pretty strong motivation right there
. But there are some limitations to a CMF driven unit (depth, potential to have the orifice get jammed up, too high an INP on the blocked reg, etc).
An eCCR also makes sense, but it has some limitations too (do you trust HAL 9000? buoyancy shifts when the solenoid fires, solenoid firing when you don't want it to causing a oxygen spike -- such as going over a hill, etc). Diving an eCCR as if it were an mCCR and controlling your PO2 by manually adding Oxygen is a good way to do it. And the benefit of being on an eCCR is that if your PO2 drops below your programmed setpoint, it'll act like a parachute and fire. In practice, the way this works is I will manually maintain a PO2 0.1 to 0.2 higher than my setpoint. So if I want to do a dive and maintain a 1.2 SP, I will program the solenoid to fire at a 1.0 and then just keep the PO2 up by manually injecting O2 when it's time.
The solenoid as a parachute is a good thing, and I can understand the desire to add a solenoid to an mCCR in order to gain that parachute, but in my opinion, adding a CMF to an eCCR is a waste of time and does nothing beneficial for you but add the negatives of diving a CMF based unit.
Please understand, my views are based on my limited CCR experience (about 400 hours, 250 of which were on a strict mCCR and 150 on a pure eCCR), so others with more experience, especially on hybrid units, may have a different viewpoint.