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Thread: Making air

  1. #11
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    NW diver we accept the risk of hypo/hyperoxic gas every single time we blend nitrox, trimix, or dive a rebreather.

    Yes it's a procedure that needs following but it's not exactly insurmountable.

    Quote Originally Posted by Dave1w View Post
    If you are blending the N2 into oxygen, then there could then be a risk if the N2 is contaminated, and it meets high pressure O2

    I wonder if heat from decanting N2 into say 40 bar of pure O2 is dangerous if done quickly - tyres filled with air on large mining trucks explode with heat? Anyone know?
    Tyres on plant get blown up with a cheetah tank to bang as much air as possible in there as quickly as possible to seat the bead. They are great for making spud guns. The idea of an explosion from the heat involved is preposterous. (and you can literally blast tyres onto the rims with flammable gas explosions and they're fine)

    N2 contaminated? It's exactly the same level of risk as the oxy or helium being contaminated, which we all take as a completely acceptable risk. And very probably much lower risk than the risk of a compressor filter failure.*

    *which happen, regularly. Remember the recent one about the pool full of scouts getting gassed with monoxide and needing treatment? When was the last time we heard of contaminated helium? Ever?



    Yes fine this method is not going to be universally accepted or convenient, but ffs let's not go making up safety issues off the top of our heads without a dose of realism about it.

  2. #12
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    Quote Originally Posted by taz View Post
    Is it safer to always blend into the O2?
    Cause I never thought of that side off it

    taz

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    Yes as the pressure's lower.

    Keep the transients sensible and all that's happening inside the tank is a load of mixing as the gas comes in. The oxy is rapidly diluted and the major risk is debris coming down the valve and impacting the far wall creating enough heat. The odds of that are way lower (IMO) than the risks associated with dealing with O2 at very high pressure in the valve area (which being full of flammable shit like plastic, O rings and grease) is the most dangerous.

  3. #13
    Established TDF Member taz's Avatar
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    Quote Originally Posted by WFO View Post
    I'm with you about getting a compressor.

    Except why is decanting Nitrogen unsafe?
    No risk of oil contamination, much less heat of compression, no risk of sucking in vehicle fumes, no risk of an oxygen fire decanting it. If anything the only increased risk is doing your back in moving an extra J cylinder.

    Time? Really? A toy compressor will take 20 minutes to do your air top. From a bank (of nitrogen) you could do that in 20 seconds if you wanted. (ok let's not start on the time taken to go and get the J of nitrogen)


    BUT

    If you actually want to do it, then get your N2 from Energas as they do inerts at 300bar.

    You will need the daft euro coupling which may be different from the helium one but I don't know.
    I have access to compressors, both personal and club but I also have access to unlimited amounts of gas (not Helium unfortunately)

    The N2 is pure at 99.9% and is referred to as OFN in my trade (oxygen free nitrogen) so is classed as dry nitrogen
    or dehumidified nitrogen. The O2 is commercial grade not medical but I've found that commercial O2 and Medical O2
    come from the same source and Medical has one extra level of security because it goes into a medical cylinder and
    not a rusty steel jobby that most BOC cylinders tend to be.



    So given those perimeters, if somebody wanted there would be no other reason why not??

    taz

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    Quote Originally Posted by taz View Post
    The O2 is commercial grade not medical but I've found that commercial O2 and Medical O2
    come from the same source and Medical has one extra level of security because it goes into a medical cylinder and
    not a rusty steel jobby that most BOC cylinders tend to be.
    The paper trail which comes with diving / medical o2 is the biggest difference. I use industrial O2 for my CCR.

    No reason not to do what you suggest although if you've got compressors then that would be the preferable / easiest option.

    YOU MUST analyse the gas properly.
    If you're going through the hassle, you might as well make nitrox out of it.

    Like I said, I think your biggest issue is going to be losing the high pressure in your o2/N cylinders. The ones BOC supply me usually only come with 200b. You're not going to get many good fills out of that without a booster.

    EDIT: Back of fag packet calc says that if you've got 50L 200bar o2 and N supply cylinders, the first time round you'll get a 12L fill at 178b. Second time you'll get 160bar.

    You lose that top end pressure really quick. Not normally such an issue with blending as you're topping the gasses up with a compressor
    Last edited by NWdiver; 13-06-2019 at 01:02 PM.

  5. #15
    Established TDF Member taz's Avatar
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    Quote Originally Posted by NWdiver View Post
    The paper trail which comes with diving / medical o2 is the biggest difference. I use industrial O2 for my CCR.

    No reason not to do what you suggest although if you've got compressors then that would be the preferable / easiest option.

    YOU MUST analyse the gas properly.
    If you're going through the hassle, you might as well make nitrox out of it.

    Like I said, I think your biggest issue is going to be losing the high pressure in your o2/N cylinders. The ones BOC supply me usually only come with 200b. You're not going to get many good fills out of that without a booster.

    EDIT: Back of fag packet calc says that if you've got 50L 200bar o2 and N supply cylinders, the first time round you'll get a 12L fill at 178b. Second time you'll get 160bar.

    You lose that top end pressure really quick. Not normally such an issue with blending as you're topping the gasses up with a compressor
    See there you go again with a reasoned argument as to why not do it?



    Good points and well put

    I was just thinking while reading other posts about secondary filtration and personal filters and the such

    taz

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    So it's even more difficult than I thought. Assuming again the 50L 200bar o2 and N supply cylinders and 12L diving cylinder.

    If you're filled the 12L with o2 up to 52 bar. This would reduce your o2 bank down to 187 bar for your next fill.
    Then if you decanted from the N bank until it equalized you would end up with 171 bar in both your 12 litre and diving cylinder. The diving cylinder would end up with a mix of 30.3%.

    As you can see, the issue is with the Nitrogen. Not only do you lose that high pressure quickly (next fill would be lucky to get above 150b), not knowing exactly what your final pressure will be makes the gas blending difficult. You basically just need to stick o2 in and the water it down and hope you get approximately the mix you want.

    Basically, unless you have much higher pressure nitrogen (or o2 if you mix the other way) or a booster, it's not going to be practical.

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    Quote Originally Posted by NWdiver View Post
    As you can see, the issue is with the Nitrogen. Not only do you lose that high pressure quickly (next fill would be lucky to get above 150b), not knowing exactly what your final pressure will be makes the gas blending difficult. .
    Get better at maths then

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    Quote Originally Posted by WFO View Post
    Get better at maths then
    I get paid to do maths... I'd rather not do anymore when I don't have to

  9. #19
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    If you really want to make "air", then you'll also need to source and mix in ~1% water vapour, 1% argon, 0.04% carbon dioxide, plus trace amounts of neon, helium, methane and krypton, dust, aerosols and other pollutants. It's a bit hard to know why you would want to make this artificially since there is about 5 million billion tons of it readily available premixed on Earth as a natural resource.

    If on the other hand what you want to make is 21% Nitrox, then sure, the ingredients you need are oxygen and nitrogen. Cost benefit calculations are up to you.

  10. #20
    Gimme a medal BenL's Avatar
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    Forget the diving but. Making air out of its real constituent parts might be a moneymaking for the gaming/hipster community. Hear me out: VR technology will soon replace being out and about in the real, Physical world for some. Pipe in a whiff of the Dolphin Inn, or the beach, on those conference calls (for a premium, obviously) and you're into 21st century smellyvision - I think it's marketed as "4D" these days.
    I don't want to get technical or anything, but alcohol IS a solution


 
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