Heliair+

I came across this article on Heliair http://www.advanceddivermagazine.com...oorMansMix.pdf

And starting thinking what would happen if you mixed your own helium with Nitrox. Started crunching numbers based on the figures under "Best Mix" and came up with just a hair over EAN32. This would give you an END of 130 ft with a ppO2 at MOD of 1.4-1.6.

I don't know enough about gas mixing to calculate out the real (useful) figures (MOD, beginning He PSI). But for someone who does (and is trained in deep mix diving), this seems like a cheap way to dive home brewed trimix.

Am I way off, or does anyone do this?

been done before and is going on bro. go to airspeedpress.com

enjoy. I did but haven't gotten into mixing it yet.

With He and 32% nitrox it is easy to make a some very handy mixes. Examples include 21/35, 18/45, and 15/55.

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Originally Posted by Greenwood_60

I came across this article on Heliair http://www.advanceddivermagazine.com...oorMansMix.pdf

And starting thinking what would happen if you mixed your own helium with Nitrox. Started crunching numbers based on the figures under "Best Mix" and came up with just a hair over EAN32. This would give you an END of 130 ft with a ppO2 at MOD of 1.4-1.6.

I don't know enough about gas mixing to calculate out the real (useful) figures (MOD, beginning He PSI). But for someone who does (and is trained in deep mix diving), this seems like a cheap way to dive home brewed trimix.

Am I way off, or does anyone do this?

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There's really nothing 'cheap' about it. You use the same amount of He and O2 whether you put the O2 in directly, or whether its part of the top off. It you've got the equipment to PP fill He, you have the equipment to PP fill O2 also. The only question is how many tanks you want to have in your garage.

Tom

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Originally Posted by b1gcountry

There's really nothing 'cheap' about it. You use the same amount of He and O2 whether you put the O2 in directly, or whether its part of the top off. It you've got the equipment to PP fill He, you have the equipment to PP fill O2 also. The only question is how many tanks you want to have in your garage.

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Cheap vs an LDS mixing or banking it for you. And I already have an O2 and Acetylene tank, why not one more. :)

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Originally Posted by Greenwood_60

Cheap vs an LDS mixing or banking it for you. And I already have an O2 and Acetylene tank, why not one more. :)

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First off, you're gonna need a lot more than just one more if you want to PP blend trimix.

Second off, you will save money on the Helium, but you do need somewhere to fill them. It's best if they know what you're doing so there's no misunderstandings. I can give you a couple more tips if you'd like. I've got 8 bottles in my garage that I transfill from.

Tom

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Originally Posted by Greenwood_60

Cheap vs an LDS mixing or banking it for you. And I already have an O2 and Acetylene tank, why not one more. :)

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A lot of folks are doing this. PP He and O2 and then air top off at the dive shop.

I used to do that in Miami. I had built a simple fill whip and always had 3 He and 3 O2. I did EAN 32, EAN 50 and 21/35 with this. The savings are relative to how cheap you get your He. I always told the shop about it, mostly because of the EAN mix (pure O2 in the tank). For trimix, it does't really matter much since it's mostly He and a bit of O2. I had some shops no wanting to top off (they did PP so it was mostly an issue of $$$ although they blamed it on safety of my breathing gas). Had to "shop" around until I found a shop that didn't care.

As said before, I don't see the point of just using He and top off with nitrox. Might as well rent some O2 tanks and buy the extra tank adapter so you can mix whatever you want.

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Originally Posted by chimie007

I don't see the point of just using He and top off with nitrox. Might as well rent some O2 tanks and buy the extra tank adapter so you can mix whatever you want.

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Coming from a math point of view choosing a mix with a certain ppN2 and ppO2 limit at max depth is just a matter of filling the equivalent nitrox and ballance of He.

If your target is ppO2 1.4 with END of 100' 32% is the Nitrox mix at 100' - with no He.

At all deeper depths it is just a matter of diluting the same with He.

For 100' or deeper it would be hard to get more convienient than banked nitrox plus He.

It works nicely with banked 32 % ean --

this is a direct proportional dilution of the oxygen content and nitrogen content with helium.


take empty cylinder - put in a portion of helium ....... say half the tank 1750 psi -- top with ean 32 and poof you have 16/50 (ish)

take empty cylinder - pit in a portion of helium ........ say 35 % of the tank 1225 psi -- top with ean 32 and poof you have 21/35(ish)

variations will be based on compressiblity and speed of fill .......

in the NOAA Diving Manual we illustrate this method with EAN 36 since we were making 18/50 (18 = 1/2 of 36)

Cheers