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Thread: Use of Heliox in Drager

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    New Member EDB is an unknown quantity at this point EDB's Avatar
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    Use of Heliox in Drager

    I have come across some references to the use of Heliox (not trimix) with the Dolphin. The benefits would be that Heliox like Nitrox is a two gas mixture, which would generate a stable flow pattern through the sonic oriface (the suggested danger in trimix is that shooting three different sized molecules through the orifice is unstable and unpredictable from moment to moment) and monitoring PPO2 would be sufficient for calculating decompression.

    Anyone out there personally used Heliox in the Dolphin? I'm really looking for a way to dive comfortably in the 150' to 200' foot range (where I currently use oc trimix and doubles).

    EDB

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    Quote Originally Posted by EDB
    I have come across some references to the use of Heliox (not trimix) with the Dolphin. The benefits would be that Heliox like Nitrox is a two gas mixture, which would generate a stable flow pattern through the sonic oriface (the suggested danger in trimix is that shooting three different sized molecules through the orifice is unstable and unpredictable from moment to moment) and monitoring PPO2 would be sufficient for calculating decompression.

    Anyone out there personally used Heliox in the Dolphin? I'm really looking for a way to dive comfortably in the 150' to 200' foot range (where I currently use oc trimix and doubles).

    EDB
    There really is no difference running, nitrox, heliox or trimix through a sonic orifice.. the Danger is that the flow reading you will get on a typical flow meter will be quite wrong with heliox and trimix due to the lighter He molecule.. You gave to calculate what the atomic weight of the gas mixture you plan on using and scale it to the flow meter you are using.

    Oxygen and Nitrogen are very close in atomic weight so the difference on aguage calibrated for air flowing 50% through it is not that great.. Helium is radically lighter than wither oxygen or nitrogen and there is a big difference in measured fow and actual flow..

    Also to be able to dive it safely at depth you should really be using an alternate mix (preferrably oc) to get you to depth and to do your deco on..



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    New Member EDB is an unknown quantity at this point EDB's Avatar
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    Thank you for that insight; I had been worried that with trimix you would not be able to reliably calculate the relative concentrations of N and He which would make decompression calculation a problem or leave one vulnerable to unanticipated narcosis.

    I understand the need for carrying separate decogas (oc); are you advocating additional travel gas out of concern for hypoxia on descent?

    I'm a few years away from being able to afford the move to CCR, love my Dophin and Ray and am just looking to get to 150' or so for some of the wrecks out here.

    EDB

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    Quote Originally Posted by EDB
    Thank you for that insight; I had been worried that with trimix you would not be able to reliably calculate the relative concentrations of N and He which would make decompression calculation a problem or leave one vulnerable to unanticipated narcosis.

    I understand the need for carrying separate decogas (oc); are you advocating additional travel gas out of concern for hypoxia on descent?

    I'm a few years away from being able to afford the move to CCR, love my Dophin and Ray and am just looking to get to 150' or so for some of the wrecks out here.

    EDB
    Yes I advocate a travel gas for two reasons, first the risk during descent and if there is a problem with the deco gas you still have something that is breathable



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    Quote Originally Posted by jradomski
    There really is no difference running, nitrox, heliox or trimix through a sonic orifice.. the Danger is that the flow reading you will get on a typical flow meter will be quite wrong with heliox and trimix due to the lighter He molecule.. You gave to calculate what the atomic weight of the gas mixture you plan on using and scale it to the flow meter you are using.
    You got me Joe, can you explain this in more detail preferably quantitative. I dont see why the flow rate in a flow meter should be different depending on the gas mixture?

    A gas flow is a gas flow, surely and it doesnt matter what gas it is? Why does the weight of the molecules have a bearing on actual vs measured flow rate. I admit I have a degree in physics but dont remember much of it...

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    Quote Originally Posted by Andy M
    You got me Joe, can you explain this in more detail preferably quantitative. I dont see why the flow rate in a flow meter should be different depending on the gas mixture?

    A gas flow is a gas flow, surely and it doesnt matter what gas it is? Why does the weight of the molecules have a bearing on actual vs measured flow rate. I admit I have a degree in physics but dont remember much of it...

    I am not going to go into a long description since there is a real good one posted here.. This is also why there are SO many different flow meters out there, they are all for specific gases..

    http://www.therebreathersite.nl/gas_...an_orifice.htm

    The section you are interested is a bit further than halfway down...



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    Quote Originally Posted by jradomski
    I am not going to go into a long description since there is a real good one posted here.. This is also why there are SO many different flow meters out there, they are all for specific gases..

    http://www.therebreathersite.nl/gas_...an_orifice.htm

    The section you are interested is a bit further than halfway down...
    What about using the old fill bag method used with the Atlantis? That method should give better result.
    Cheers,

    Dave....

    www.wedivebc.com

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    Quote Originally Posted by jradomski
    I am not going to go into a long description since there is a real good one posted here.. This is also why there are SO many different flow meters out there, they are all for specific gases..
    Quote Originally Posted by jradomski

    http://www.therebreathersite.nl/gas_flow_through_an_orifice.htm

    The section you are interested is a bit further than halfway down...


    Thanks for the link, Joe. Very interesting reading. I must say that I found the article by Nevil Adkins to be more informative.

    Cheers!

    Rob

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    Quote Originally Posted by ROB DAVIE

    Thanks for the link, Joe. Very interesting reading. I must say that I found the article by Nevil Adkins to be more informative.

    Cheers!

    Rob
    They each bring up good points, but the first link is the only one that describes the flow meter and I knew there was a link to the other article at the bottom..



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    Quote Originally Posted by wedivebc
    What about using the old fill bag method used with the Atlantis? That method should give better result.
    The old fill method gets you in the ballpark because its a judgement call, If I am planning deco I want to be as close as possible so I know what the true low po2 to expect.

    if you have a good flow meter, and know how to scale it you will get more precise results..

    Its no big deal if you decide on some fairly standard mixes and learn the scaling factors for those mixes, a few % either way is not going to make a great difference.. but no helium to say 25% helium makes a difference...



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