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Bottle-to-bottle charging

Discussion in 'Anything Airgun Related' started by spranynpray, May 11, 2014.

  1. spranynpray

    spranynpray Member

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    Hi all,

    I have two bottles - a 3 litre and a 9 litre. The 9 litre is hostile to carry, the 3 is OK. Both bottles are in need of a test, and both have only sat in my house since they were last charged (and since certification last time, charged only once). Personally I think it is unnecessary and a rip-off to pay out for both to be certified and charged, so I'm thinking of just getting the 9kg done and using it to charge the 3kg. I would like your views on this practice, and also guidance as to where I can buy the parts to effect the bottle-to-bottle charge please.

    Thx.
     
  2. Kenbarcon

    Kenbarcon Donator

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    Thats what lots of people do, keep the larger bottle in test and use the smaller without test for topping up when you need too,
     
  3. Mart61

    Mart61 Pro Poster

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    Personally I think the practice would be madness if either bottle is out of test. Mind you it would be funny to see the results of the out of test bottle explode when charged.

    The tests are done for a reason and if you can't or are unwilling to afford a recharge, perhaps you should stick to springers.
     
    Last edited: May 11, 2014
  4. oliver13

    oliver13 Donator

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    I can't see a real problem, the cylinder won't fail unless it's been abused or neglected for years so you will be OK there, the only thing is the pressure, a 300bar 9L cylinder will charge a 3L one to 225bar which is fine at first but usable pressure may soon become an issue.
     
  5. NorfolkDave

    NorfolkDave Donator

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    You can get one of these. http://www.bestfittings.co.uk/shopexd.asp?id=284 bit pricey, I think there's also a cheaper one without the bleed which is what I use, but check whether you're going to need the bleed or not. Wouldn't advise using an out of test cylinder, it's a bit like not MOTing your car.

    Dave
     
  6. spranynpray

    spranynpray Member

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    Really? I'm surprised to read this. Can't see why there is a loss across the decanting hose or is the difference due to heating (which will equalise)?
     
  7. 18 Wheeler

    18 Wheeler Busy Member

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    The above assumes that the 3 litre cylinder is empty and the result is simply due to the increased total volume occupied by the air (9 to 12 litres) and is not due to any loses/heating.

    It's an easy calculation. (Assumes perfect gas behaviour etc, but close enough for our purposes).

    9 ltr @ 300BAR = 2700 ltr at 1 BAR, divide that by your new volume 12 ltr = 225BAR.

    In the real world you would only be topping off the smaller cylinder.

    With a starting pressure of say 180BAR in the 3ltr (540 ltr @ 1 BAR) and 300 BAR in the big tank you have a total volume of:
    2700+540= 3240

    3240/12 = 270 BAR equalised pressure.

    Next time around the 3 litre will again have 540 ltr, the 9 litre now has 2430 ltr,
    2970 ltr total.

    2970/12 = 247.5 BAR equalised pressure etc
     
    Last edited: May 11, 2014
  8. Scott srs

    Scott srs Well-Known Member

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    I was told by a guy at the dive centre I know that the test is only needed for bottles that get used under water. as deep water ads extra pressure and for someone with a good clean bottle using for filling a airgun it's a con he fills mine without a test
     
  9. oliver13

    oliver13 Donator

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    I don't think he knows what he's talking about so don't take his advice on it's own, but if he's happy to fill an out of test cylinder for an airgunner that sounds like a good chap to know
     
  10. roy0110

    roy0110 Engaging Member

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    when i had a bottle out of test, the guy that used to fill it for me told me to put a label on it stating "for air rifle use only"
    he was happy to fill it after that without test.
    i just took his word for it thinking he knew what he was talking about.
     
  11. spranynpray

    spranynpray Member

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    Gotcha. I had my brain turned off there for a while! So if I were to do this it seems I would need a much bigger bottle to really gain out of it which sounds. To hell with it - I may go back to plan 'a' and get a carbon fibre bottle with a long test as the cost of re-charges isn't expensive, I just hate being ripped off for a re-test when the bottle has had the same dry air in it for the last 5 years!
     
  12. harry brown

    harry brown Banned

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    This is a classic explanation/reason of why I should have listened during maths lessons...Instead of looking at A.B's lovely firm Baps for the whole lesson 37-8 years ago! :rolleyes:.....:confused:......:)
     
    Last edited: May 11, 2014
  13. Barni

    Barni Donator

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    Miss A was my biology teacher ..... oh my word !! i say no more


    but a sticker " for air rifle use only " ...... now that could be of use :) i wonder if we could get that rule to work ?
     
  14. DaveF

    DaveF Busy Member

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    From your original post doesn't sound like you shoot that much so why not stick to the 3ltr bottle and sell the 9ltr. decanting from 9ltr to 3 ltr is pointless you would only get 1 good refill.

    The test is for a very good reason, when us airgunners buy these bottles we are never given a saftey brief or told how dangerous they can be. My refiller who does tank tests, is an air gunner and taught me a lot. its like carrying a potential bomb around. tanks must be kept cool not in sunlight or a hot car. most people have no idea of how dangerous 300bar compressed air is. there are videos on utube. as far as carbon fibre tanks are concerned the test on these is even strickter, any scratches or chips in carbon rap is an instant fail and these the tanks have a much shorter life span
     
  15. cloverleaf

    cloverleaf Super Moderator Staff Member Mod/Admin

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    The most highly stressed part of a cylinder is the internal wall, so it's here where corrosion or damage will have the greatest effect. It will take significantly less corrosion on the inside of the cylinder than the outside to cause it to fail.

    Internal corrosion can be caused by the entry of seawater when empty, or more relevantly to us through filling with damp air. The greater danger from seawater is why sub-surface bottles are tested at 2.5yr intervals rather than the 5yrs for surface bottles.

    Being used on the surface does not exempt bottles from testing! It's still highly possible that they can be corroded on the inside by wet air; damage that will only be found during testing or when it goes pop and takes your face with it..
     
    Martman likes this.
  16. spranynpray

    spranynpray Member

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    Gotcha. I had my brain turned off there for a while! So if I were to do this it seems I would need a much bigger bottle to really gain out of it which sounds. To hell with it - I may go back to plan 'a' and get a carbon fibre bottle with a long test as the cost of re-charges isn't expensive, I just hate being ripped off for a re-test when the bottle has had the same dry air in it for the last 5 years!
     
  17. SteveO

    SteveO Top Poster

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    My guy re-painted my black and white bottle to grey (industrial air colour), the tank has a 10 year ticket now, and only needs a 5 yearly visual inspection until it needs certifying again. The colour change is done to prove that it wont be used under water for breathing air purposes.
     
  18. Mart61

    Mart61 Pro Poster

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    The voice of sanity...
     

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