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  1. #1
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    Decanting Pressure question

    So if I have an 11 litre cylinder pumped to 200 bar & decant into an empty 12litre twinset how much pressure would I equalise out at ? I have 2 theories one ends up at 45 bar the other at 62 bar ?
    I trust my rebreather implicitly I just don't trust the owner

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  2. #2
    Sorry for being a dick jb2cool's Avatar
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    62.8bar but if you get creative with the isolator you can increase this to 70.6 (I think).

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    You have a total volume of 11+(12*2)= 35L

    You have 200*11= 2200 litres of gas

    2200/35= 63 bar

    Both your twinset and your 11L will end up with 63 bar in them

    --------------------------------

    With the manifold closed, you could decant into one side of the twinset first. Then decant into the other side before opening the manifold.

    In which case...

    decanting into first side 2200/23 = 96 bar in first side

    This leaves you with 96 bar in the 11 so 96*11 = 1056 litres of gas

    decanting into second side 1056/23 = 46

    Open the manifold... (96+46) /2 = 71 bar

    In this case you'd have 46 bar in the 11 and 71 bar in the twinset

  4. #4
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    Quote Originally Posted by colinicky View Post
    So if I have an 11 litre cylinder pumped to 200 bar & decant into an empty 12litre twinset how much pressure would I equalise out at ? I have 2 theories one ends up at 45 bar the other at 62 bar ?
    The pressures have to be equal if you equalise. Just add the volumes together and dive smallest by the total, then multiply by starting pressure

    24+11 = 35L

    11/35 = 0.3142

    0.3143*200 = 62.84bar

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    The formula is P1 x V1 = P2 x V2

    P1 (pressure 1) x V1 (Volume 1) = P2 (pressure 2) x V2 (Volume 2)

    So pressure 1 is 200 bar x Volume 1 11 litres= 2200

    We know V2 is 11 litres plus 24 litres = 35 litres so to solve for P2 (the resulting pressure) divide 2200 by 36 = 62.8 bar

    If the twinset had air in it to start, say 100 bar, you would total the volume of air across both cylinders i.e. 2200 litres in the 11 litre plus plus 2400 litres in the twinset = 4600 litres divided by the total volume of 35 litres to give a resulting pressure of 131.4 bar

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    Established TDF Member Paulo's Avatar
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    Everyone seems to be forgetting the effects of Charles Law
    Remember anything you read on the internet was probably written by some guy sitting at home in his underpants! Including this !!

    Illegitimi non carborundum

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    TDF Member Alex Denny's Avatar
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    Quote Originally Posted by Paulo View Post
    Everyone seems to be forgetting the effects of Charles Law
    Leave it so they both return to ambient temperature?

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    Charles, Gay-Lussac and Boyles law are really just special cases of the ideal gas law with one of the variables held constant. I can never remember which is which and always think them all as PV=nRT.



    Quote Originally Posted by Paulo View Post
    Everyone seems to be forgetting the effects of Charles Law

  9. #9
    Established TDF Member Paulo's Avatar
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    Charles Cooks
    Boyle Bubble
    Daltons Partial Pressure
    Henry is the other one - solubility
    Remember anything you read on the internet was probably written by some guy sitting at home in his underpants! Including this !!

    Illegitimi non carborundum

  10. #10
    Old but keen Mark Chase's Avatar
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    Quote Originally Posted by NWdiver View Post
    You have a total volume of 11+(12*2)= 35L

    You have 200*11= 2200 litres of gas

    2200/35= 63 bar

    Both your twinset and your 11L will end up with 63 bar in them

    --------------------------------

    With the manifold closed, you could decant into one side of the twinset first. Then decant into the other side before opening the manifold.

    In which case...

    decanting into first side 2200/23 = 96 bar in first side

    This leaves you with 96 bar in the 11 so 96*11 = 1056 litres of gas

    decanting into second side 1056/23 = 46

    Open the manifold... (96+46) /2 = 71 bar

    In this case you'd have 46 bar in the 11 and 71 bar in the twinset


    What he said


 
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