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Thread: Conversion of Cylinder sizes

  1. #11
    RBW Member decoweenie has a reputation beyond repute decoweenie has a reputation beyond repute decoweenie has a reputation beyond repute decoweenie has a reputation beyond repute decoweenie has a reputation beyond repute decoweenie has a reputation beyond repute decoweenie has a reputation beyond repute decoweenie has a reputation beyond repute decoweenie has a reputation beyond repute decoweenie has a reputation beyond repute decoweenie has a reputation beyond repute decoweenie's Avatar
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    Re: Conversion of Cylinder sizes

    Quote Originally Posted by 2002scubasteve  View Original Post
    How can this be?
    Since you divide by a higher pressure, obviously you get a lower displacement L.

    As the Imperial unit gives the rated capacity (in 95 cf, for example) at certain rated pressure. They go hand-in-hand and must be used together.

    The moment you raise the pressure, the rated capacity is no longer the same (at 95 cf). It should increased.

    In Metric unit, the L is the equivalent water displacement of the tank. So multiplying by pressure gives you the internal gas capacity.

    For example, there are 7L with 200 bar tanks, and also 7L with 223 bar tanks available. The external size of these 2 tanks are the same and should displace the same amount of water when submerged.

  2. #12
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    Re: Conversion of Cylinder sizes

    Quote Originally Posted by decoweenie  View Original Post
    This is a rough calculation...
    • Convert cf into free liters using: cf * 28.3 = free liters
    • Convert rated pressure into bar using: psi / 14.5 = bar
    • Convert free liter at pressure into displacement: free liter / bar = L
    For example, 80cf 3200psi into Metric equivalent:
    • 80cf * 28.3 = 2,264 free liters
    • 3200psi / 14.5 = 220 bar
    • 2264 free liters / 220 bar = 10 L
    As said, just roughly... ;)
    except most al "80s" are actually 77.4 cuft when using air..
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    Re: Conversion of Cylinder sizes

    Quote Originally Posted by 2002scubasteve  View Original Post
    I have used the conversion formula given here cuFT/0.035/rated pressure,but I don't understand that a tank with lower pressure holds more liters? Example: a 95 steel tank with 2400psi(165.474bar) holds 16.40 liters.
    same tank at 2650 holds 14.85 liters according to this formula. How can this be?
    In the us the tanks are rated at the 10% overfil capacity (2640 vs 2400).. so one you lose the + rating it falls back to the normal working pressure so it no longer a 95 its 10% less.. at 2400 a "95" is not a 95..
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  4. #14
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    Re: Conversion of Cylinder sizes

    Quote Originally Posted by decoweenie  View Original Post

    For example, there are 7L with 200 bar tanks, and also 7L with 223 bar tanks available. The external size of these 2 tanks are the same and should displace the same amount of water when submerged.
    Actually the internal size is the same and they should hold the same ammount of water if you filled them with water.

    Not really an important distinction, but what the hey.

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    Re: Conversion of Cylinder sizes

    Quote Originally Posted by jradomski  View Original Post
    Quote Originally Posted by decoweenie  View Original Post
    This is a rough calculation...
    • Convert cf into free liters using: cf * 28.3 = free liters
    • Convert rated pressure into bar using: psi / 14.5 = bar
    • Convert free liter at pressure into displacement: free liter / bar = L
    For example, 80cf 3200psi into Metric equivalent:
    • 80cf * 28.3 = 2,264 free liters
    • 3200psi / 14.5 = 220 bar
    • 2264 free liters / 220 bar = 10 L
    As said, just roughly... ;)
    except most al "80s" are actually 77.4 cuft when using air..
    Aluminum 80s are 77.4 cu ft (assuming a 3000 psi fill). The "neutrally Bouyant" AL 80s are 77.4 cu ft when filled to 3300 psi, their normal fill preasure. Those two tanks have a liquid capacity of 11.11 and 10.32 liters respectivly.

    Your best bet is to scour through tank specification pages unit you find the actual liquid capacity for the tank. Then use that with the conversion factors above to find out the real capacity in free liters or cu ft, which ever way your bread is buttered.

    Also you will need that real capacity to acuratly calculate SAC rates, otherwise the preasue used while doing the test is meaningless.

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