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  1. #46
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    Quote Originally Posted by Turnup View Post
    Not so. The coefficient of expansion of all gasses is the same provided that the gas is not at a pressure or temperature close to a phase change (condense, evaporate, or solidify). This is easily verified using google.

    There is some controversy over the use of Nitrogen in tyres and I have not been able to find any satisfactory explanation other than for tyres used in extreme conditions. Aircraft tyres run at typically 200 psi and at that pressure oxygen becomes much more reactive - this might also be the case for truck tyres. For car tyres = snake oil.

    Racing car tyres run at very low pressures and I have been unable to understand why they use N - even the thermal conductivity of N and air are very nearly the same. It may be that they have always done it this way.
    That was the way that Michelin explained it be it right or wrong in the terms of physics.
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  2. #47
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    Quote Originally Posted by Scubashot View Post
    As far as I am aware the largest available 300 bar scuba cylinder is only 12 litres, which does still contain more gas than a 232 bar, 15 litre cylinder.

    I am not sure how compressed nitrogen gas is produced commercially but I would imagine that compressors are involved at some point.
    We certainly use molecular filters with some dive compressors to reduce the nitrogen content of our breathing gas. It is an alternative method of producing enriched air (nitrox), rather than putting a specified pressure of pure oxygen into a tank before topping off to the required pressure with air.

    As long as appropriate water filters are incorporated into the compressor then air is certainly dry enough for use in any air gun. It is also widely and cheaply available from many different outlets.


    on large scale they do it by cooling air until it liquifies, then they warm it up and distill its fractions/components. On small scale yes you can have a nitrogen generator/which uses compressors with membranes
    (usually there are 2-3 compressors in the unit, which are likely to fail and if one failes, the other 2 keep it going for a while.) compressors all fail if not maintained often. Expensive. yes the water will condense out in the process so if you lead it out, the end product is drier than the ambient air. the inline filtering is a futile process the filter medium saturates fast, you will have to mess around with the desiccant way too often.

    ...my example with the 15L bottle was the unrealistic large N2 bottle versus a very small room, i would say you could get a headache from it max. If any at all. Dont do it in the cupboard, with the doors shut behihnd you. lol
    If you have a large man size bottle, yes have it somewhere where it is not fully enclosed. With good ventilation. Commons sense.

    I am not saying scuba air is bad, but i would not recommend steering clear of any compressors. Too much wear and tear and high costs. I am also a scuba diver, these two hobbies go well along. True.
    Last edited by krisko; 07-04-2018 at 05:04 PM.

  3. #48
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    Quote Originally Posted by ballisticboy View Post
    No one seems to have pointed out that if he uses nitrogen to fill his rifle he will be committing an offence as only air and CO2 are permitted, all other gasses I believe are excluded.
    Very good point, although the likelihood of detection would seem to be very low unless there was a confession.
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  4. #49
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    Quote Originally Posted by krisko View Post
    on large scale they do it by cooling air until it liquifies, then they warm it up and distill its fractions/components. On small scale yes you can have a nitrogen generator/which uses compressors with membranes
    (usually there are 2-3 compressors in the unit, which are likely to fail and if one failes, the other 2 keep it going for a while.) compressors all fail if not maintained often. Expensive. yes the water will condense out in the process so if you lead it out, the end product is drier than the ambient air. the inline filtering is a futile process the filter medium saturates fast, you will have to mess around with the desiccant way too often.

    ...my example with the 15L bottle was the unrealistic large N2 bottle versus a very small room, i would say you could get a headache from it max. If any at all. Dont do it in the cupboard, with the doors shut behihnd you. lol
    If you have a large man size bottle, yes have it somewhere where it is not fully enclosed. With good ventilation. Commons sense.

    I am not saying scuba air is bad, but i would not recommend steering clear of any compressors. Too much wear and tear and high costs. I am also a scuba diver, these two hobbies go well along. True.
    Well almost, "Air" doesn't liquefy, but the two major components Nitrogen & Oxygen do, so in simple terms you make compressed air work very hard & the only energy it can use to do that work is heat energy so it cools & eventually you "cold distil" the two liquids off & store them in insulated tanks.
    Cylinders are then filled by allowing the liquid to warm & "gassing off"

    At least that's how the RAF plants worked.

  5. #50
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    sorry, if you take away heat from a gas, in my vocabulary it is called cooling.

    The gas will condense first i.e. turns into liquid, if you continue to cool it lower, it will turn into solid. If there are more components of course these will happen at different temperatures. Helium will freeze all gases to solid, that's why it is difficult to handle, more difficult than liquid nitrogen.
    Angrybear are you saying that it is not cooling, I am not exactly familiar with how the process itself is done so the air does Liquefy. They compress it, dissipate the heat produced, then expand it to release its stored energy further.

    In the end it is still freaking COOLING AND LIQUEFYING. The fridge works similarly, you compress a medium with some heat exchange and expand it in the place where you want the cooling effect no?

    by the way N2 and O2 can be called waste/by-products of rare gas production process, if you want to know it really.

    https://en.wikipedia.org/wiki/Noble_gas

    EDIT: https://en.wikipedia.org/wiki/Air_separation
    Last edited by krisko; 08-04-2018 at 12:49 PM.

  6. #51
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    Quote Originally Posted by krisko View Post
    sorry, if you take away heat from a gas, in my vocabulary it is called cooling.

    The gas will condense first i.e. turns into liquid, if you continue to cool it lower, it will turn into solid. If there are more components of course these will happen at different temperatures. Helium will freeze all gases to solid, that's why it is difficult to handle, more difficult than liquid nitrogen.
    Angrybear are you saying that it is not cooling, I am not exactly familiar with how the process itself is done so the air does Liquefy. They compress it, dissipate the heat produced, then expand it to release its stored energy further.

    In the end it is still freaking COOLING AND LIQUEFYING. The fridge works similarly, you compress a medium with some heat exchange and expand it in the place where you want the cooling effect no?

    by the way N2 and O2 can be called waste/by-products of rare gas production process, if you want to know it really.

    https://en.wikipedia.org/wiki/Noble_gas
    NO, I was just clarifying that "Air" which is a mixture of gases does not liquefy & then get warmed to distil it's component gases, as you stated .

    The individual component gases liquefy at different temperatures and are separated off as they cool, they're then purified & stored as a liquid until required, at least that's how I did it between 93-99

    No need to get so touchy over a minor correction, .

  7. #52
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    I’m an air conditioning engineer and use OFN (oxygen free nitrogen) to pressure test systems.
    OFN is dry, so that it doesn’t contaminate Ac systems with moisture.But I think I’ll stick to the recommended Air for my pcp’s. 😉

  8. #53
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    Nitrogen

    Quote Originally Posted by baldinio View Post
    See this is why I use a pump, because I'm waaay too thick to be buggering about with air cylinders
    +1

    also nitrogen is used in aircraft tyres 200+psi.
    Something to do with inert gas used to reduce
    fire risks.
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  9. #54
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    Quote Originally Posted by Gareth W-B View Post

    BOOM !!!

    Incorrect. Nitrogen is an inert gas and they use it to fill car tyres. The reason it isnt used is primarily due to cost and sourcung.
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  10. #55
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    Quote Originally Posted by eyebull View Post
    If it troubles you that much to pay £1 to fill your PCP up, you should probably chop it in for a springer.

    Bad idea. Getting a springers cylinder of nitro.....gen is a total baddass
    In a battle of wits I refuse to engage with an unarmed person.
    To one shot one kill, you need to seek the S. Kill only comes from Skill

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