Dolphin formula

[SamDiver14]

Does anyone know the mathmatical formula to figure using different gasses with different flow rates, not manufacturer recommended, for depths and or longer bottom times. What I am trying to do is write an Excel program to plug in numbers but I am missing some piece of the puzzle and I don't know which one is missing. Anyway, advice would help. My theory is that a much wider range in available than the supplied orifices and EANX mixtures would allow.

 

[narked at 90]

Does anyone know the mathmatical formula to figure using different gasses with different flow rates, not manufacturer recommended, for depths and or longer bottom times. What I am trying to do is write an Excel program to plug in numbers but I am missing some piece of the puzzle and I don't know which one is missing. Anyway, advice would help. My theory is that a much wider range in available than the supplied orifices and EANX mixtures would allow.

to find the loop mix with differant jet/mix

SUPPLY O2 x FLOW - INSPIRED O2 =

FLOW - INSPIRED =

DIVID THE FIRST BY THE SECOND = LOOP

SO LET SAY YOU HAVE TANK(SUPPLY) .40%
YOU ARE USING 50JET(flow).....7.3LT
AND A WORK LOAD(INSPIRED O2)OF SAY 1.5LT of o2 per min
WORKS OUT TO==== 1.42

NEXT

FLOW OF 7.3 - INSPIRED OF 1.5====5.8

1.42 DIVIDED BY 5.8 ==LOOP AT .24%

i hope this is what your after and i have'nt insulted you by making it simple..
best regards john

 

[JPBECK]

Not sure if I should be doing this but...

Your theory is correct--It is practiced every day by qualified (hopefully) divers:
Here is the formula---VO2 = (Qs (FsO2 - FiO2 )) / 1 - FiO2

FiO2 = ((FsO2 * Qs) - VO2) / Qs - VO2

Where:
VO2 = Oxygen metabolic rate
FiO2 = Inspired oxygen
Qs = Flow rate in lpm
FsO2 = supply oxygen percentage

Here is the Flow formula as well:

Flow (lpm) = 11Pbar * D2

Where:
P = pressure in bars
D = diameter in mm


Please dont take my word for this info--- Seek training! Don't be dumb Don't die!

This chart will give you some idea of all the different pos PO2's:
http://www.airheadsscuba.com/inspired.html

Later~

 

[SamDiver14]

Thanks guys, of course, I was overlooking the fact that the flow rate is a variable constant. Minor changes and my spreadsheet works perfectly, at least in theory.
JPBeck, of course, I have training on the Dolphin Rebreather, actually was taught by the guy that wrote the manual for TDI. Unfortunately, there is no training for using the unit in a way not intended by the manufacturer. So, don't really know if I will try. I was just interested in the theory. I actually feel pretty dumb for overlooking my mistake in figuring out the fromula. Just needed an extra few lines of constants to reference. Dumb mistake. Anyway, thanks a lot.
Sam

 

[JPBECK]

" Unfortunately, there is no training for using the unit in a way not intended by the manufacturer. "


Dont know where you heard that or who told you that but there are instructors out there that can train you how to do this kind of diving. ANDI to name one has a handful of instructors to train in said course.

Later~

 

[SamDiver14]

Joe,
What I meant by that statement was Drager is very clear in their manual that no orifice should be used with any other gas mixture than the one it is labeled for. That is why they label their orifices by the O2% they intended to flow through it. ie. the EANX 50% orifice. Of course, we are divers and like to play with the calculations and we all like to know what if I used this orifice with this mix etc. But all I am being clear about is that is unapproved use according to the manufacturer. I am nervous of instructors that would teach a class to use a device in a manner inconsistent of the manufacturers recommendations. Does that make sense?

 

[SamDiver14]

I should add, that the only rebreather courses that I have been aware of are designed for a specific brand unit, there could and maybe should be a course in basic rebreather design and function. Such a class could then cover such topics as flow rate and variable gas mix without contradicting a particular manufacturer.

 

[JPBECK]

I see-- but if there were no instructors out there teaching outside the box--all those New to Rebreather people building the KISS units would be droping like flies. There are non specific rebreather courses out there and good instructors to teach them. I dont see why having knowledge and sharing said knowledge would scare you away from them. I am only qualified to teach the Draeger unit to specs. But in the instructor course I was taught how to "Play with the Gas".

Did that chart help-- you can go pritty deep with that unit-- Here's one you havent even thought about I bet-- replace the N2 with He, lower the O2 and use a travel gas to get under. Now you are really outside the Manufacture specs! Not saying I condone such behavior of course...

Later~

 

[SamDiver14]

That is always the case right? just don't condone or recommend such behavior.
Anyway, I think that way it works in the real world is, if you are smart enough to figure it out and know how to figure it out, then you might be qualified enough to think about it. As for those guys who are building their own units, maybe they are qualified to use it since they designed it but I certainly believe that there is a hint of Darwinism in it. If you aint smart enough to build it and dive it you won't be around to recommend it to a friend. Anyway, my spreadsheet is working great now. So ... whoopeee... I can plug in any numbers I want and get an answer..... now how can I use this information to take over the world.....

 

[landfish]

the formula for figuring out what orifice and gas you want is in the tdi manual?
the dreger after alot of training,experience and thought can be used well beyond what the manufacture suggest.
you can tailor your needs to make the unit work the way you want to dive it
you need to know your motablizim rate and monitor it as you dive
my instructor included the spread sheet with the training
it is alot more reliable then me with a calculator and pen!