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tank size and pressure

Discussion in 'Advanced Scuba Discussions' started by bigolred, Jun 16, 2019.

  1. Degenerate

    Degenerate DIR Practitioner

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    Actually less.
    a 12x232 is 2784.
    A 10x300 at 270 bar is 2700, and if you go back to page 2 and take the compressibility factor into account you'll see it's even less than that.
    At 232 bar you'll suffer some from compressibility factor as well, and in the end you'll probably end up with roughly the same amount of gas, even think the 12L will come out slightly on top if you're only getting a 270 bar fill on your 10L.
    10x300 are pretty popular here in Sweden as they'll let you take a bunch of lead off your belt, and getting 300 bar fills here is never an issue.
    If you're having trouble getting fills to 300 bar where you're at, you might want to consider the 12x232 instead unless the 10x300 trims out better for you.
     
    T Mogle likes this.
  2. Storker

    Storker Divemaster

    # of Dives: 100 - 199
    Location: close to a Hell which occasionally freezes over
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    That's probably because they don't top off the tanks properly. When I fill a near-empty tank 10% above rated pressure, it's down to some 280 bar when it has cooled off. Closer to 270 when I'm in the water. Let it cool all the way down to room temp and top off, and you'll be a lot better off.

    - Some shops don't provide nitrox above 230-240 bar. You can get around that by filling 36% to 240 bar, cooling down and topping off with air. That'll give you close to 300 bar with 32%. But you need a fill whip which closes on a 300 bar valve.
     
    RainPilot likes this.
  3. T Mogle

    T Mogle Solo Diver

    # of Dives: 25 - 49
    Location: United Kingdom
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    I have not been able to try a 10x300 tank, so difficult to say how it will impact my trim.
     
  4. Degenerate

    Degenerate DIR Practitioner

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    10x300 is slightly shorter and a little bit heavier than a 12x232, so will displace less water volume so it's quite a bit more negative.
    This is great for some who are more bouyant, less good for those who are naturally heavy in the water.
    Do try and find one for rent before buying one, don't want to end up with a tank that doesn't work for you. :(
     
    T Mogle likes this.
  5. Storker

    Storker Divemaster

    # of Dives: 100 - 199
    Location: close to a Hell which occasionally freezes over
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    @T Mogle hails from the UK. There's a more than fair chance that they're diving dry. If you're diving dry, the risk of being overweighted without anything on your belt is... rather small. To put it mildly. No matter how heavy you are in the water.

    When I had my 15x300, which was a real beast and some 7 kg negative even when empty, and was diving a neo drysuit with almost no undergarments, I still had to carry a little weight on my belt. A 10x300 Faber is about 4kg negative when empty.
     
  6. tbone1004

    tbone1004 Technical Instructor ScubaBoard Supporter

    # of Dives: I'm a Fish!
    Location: Greenville, South Carolina, United States
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    circling back to the OP and I am like 4 pages behind whatever has been discussed.
    In reference to the FX133 and 3aa 108, I was granted access to the drawings for these tanks from Faber. They are both designed for 17.0 L during the manufacturing process.
    This confirms that they will be the same volume when filled to the same pressure. Doesn't matter what that pressure is, doesn't matter what amount of non-linear compression you want to apply to it, if you fill them both to 3442psi, they will have the same volume of gas, whatever that is.
     
    RyanT and rjack321 like this.
  7. BRT

    BRT Giant Squid

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    It may take more than one top off to get to 270 BAR. I fill my 3442 tanks to 3900. They usually drop to about rated pressure.
     
  8. Degenerate

    Degenerate DIR Practitioner

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    I've never dove wet so can't say much about it, I do know that a wetsuit does call for some more lead in order to sink at the surface.
    I dive D12 232 bar with a drysuit and don't need any lead at all luckily, but my mate who is in a very similar setup with bpw, drysuit and a single 12L 232 bar does need some.
    Some of the guys I dive with are also rocking D12 232 bar with drysuits and still need to add 2-4kg of lead, some people are just more bouyant (fat, really) than others :D

    Gotta say, I feel sorry for your spine for diving a 15x300, that is one beast of a bottle...
     
  9. Storker

    Storker Divemaster

    # of Dives: 100 - 199
    Location: close to a Hell which occasionally freezes over
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    I know a few who dives a D12. Many of them don't need a belt at all. I've still to meet a single tank drysuit diver who didn't need some weight on their belt. No matter their tank.

    There's a reason I sold it :)
     
  10. Degenerate

    Degenerate DIR Practitioner

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    Never seen a drysuit diver who didn't need to lead up with a single tank here either.
    Peeps diving double are a different story, though most of them need some sort of lead during winter season to counteract their thick undergarments.
    I fortunately don't, but I'm starting to get into the territory where my fat is making me too bouyant to skip extra lead :D
     

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