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tank size and pressure

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

  1. Storker

    Storker Divemaster

    # of Dives: 100 - 199
    Location: close to a Hell which occasionally freezes over
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    Sure is. We've got half a dozen of those in my family.

    Not a different breed, but of course designed and built for those pressures. My 10L 300 bar tanks weigh about as much as a 12 or a 15 designed for lower pressures (232 bar and 200 bar, respectively). To me, that's a feature because I can shave some weight off my belt while still carrying as much gas as in a 12x232 and only some 10% less than in a 15x200. But larger 300 bar tanks get really heavy. I had a 15x300 once and that was a real b*tch to schlep.

    Fill pressures are 200, 232 or 300 bar. Up here, you won't find a new steel tank rated to 200 bar, they're all 232 or 300. Hydro pressure is 150% of working pressure. On my tanks, the hydro pressure is stamped on the tank neck.

    Most common tank sizes are 10, 12 and 15L, but you can also get 7, 8.5 and 18. Probably a few others as well; Faber has a long list of tank sizes on their website.

    Typical single rigs up here are 10x300, 12x232, 12x300 or sometimes 15x200. On vacation in warmer water, I've used 12x200 and 15x200.

    Typical rec twinsets are D7x300 or D8.5x232, although I know of people with a D4x300 or a D6x300 as well. The typical tech twinset is D12x232.
     
  2. KenGordon

    KenGordon Rebreather Pilot

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    As storker says, 300 bar cylinders are different to 232 bar cylinders. I have 12l cylinders of both sorts and the 300 bar one has not left my garage in a long time. It gets tested and filled and then sits in case I need to top something up in a panic. I used to dive it and hated it due to it being particularly head heavy. In theory it being heavier saves weight on the belt but it never seems to quite work out that way in practice.

    In the U.K., and I expect the rest of Europe, the cylinders described as LP in the US are all long gone. Why would you want a cylinder which is explicitly unable to cope with the available fills? Being much lighter is only an advantage on the surface, and then a smaller ‘HP’ cylinder can carry the same gas but be easier to handle.

    Common cylinders are 10,12 and 15 litre at 232 bar, much less common 10 and 12 at 300 bar. If don’t think I have ever met a 15l at 300 bar.

    The 232 ones would be approximately HP80, HP100 and HP120 in US terms.

    Some places will give you a 250 bar fill in a 232 cylinder, and very rarely you might see 270, but I am pretty sure 300 bar in a 232 would not be done.

    The diving we do here is generally limited by tide and access. If you are going out on a boat you take enough gas for the day. If you need to dive the next day you figure out the logistics for getting a fill. Boats which are out for several days have compressors. Often you only get 200 or 210 bar fills in that situation. There is not generally room for more than two or three cylinders per diver.

    If you took a 232 bar 15 into a dive shop and asked for a 300 bar fill to enable a multi day trip they would take the piss endlessly, ring up their mates to tell them what happened and have a laugh and the next ask who told you that was a good idea so they could ridicule them too.
     
  3. Storker

    Storker Divemaster

    # of Dives: 100 - 199
    Location: close to a Hell which occasionally freezes over
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    Is that the normal length 12, or the slimmer, longer type? I've met people who are fine with the slightly longer 12x300, sometimes called a "long twelve".

    Before I sold it, one of my tanks was a 15x200. I used 3-4kg more with that than I do with a 10x300. Roughly the same weight, roughly the same capacity, noticeable difference in buoyancy.

    The only 12s I've used have been 12x200s while on vacation, so I can't speak first hand about 12x232 vs 12x300.
     
  4. KWS

    KWS ScubaBoard Supporter ScubaBoard Supporter

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    Location: SE TEXAS
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    That and I have been told that the metel alloy is different. If that were true you would think that america would go for the better allow, unless it makes the tank a lot heavier and has no market for it. I would be interesting to find out just what the differrences in euro tanks are form US tanks. I think we are actually making progress with the international tank markings to allow them in more areas thaqn teh limits that the stamp DOT ot CT places on them.
     
  5. KWS

    KWS ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: 500 - 999
    Location: SE TEXAS
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    not to mention tank wieght...
     
  6. Storker

    Storker Divemaster

    # of Dives: 100 - 199
    Location: close to a Hell which occasionally freezes over
    14,231
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    Why?
     
  7. KenGordon

    KenGordon Rebreather Pilot

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    Shhh.....

    So, there are two styles of 12 in common use in the U.K. Dumpy ones are the same diameter as a 15 and the same(ish) height as a 10. These fit shorter people kiting up on a bench. Normal or tall 12s are slimmer (same as a 10 or an ali80) and taller (taller than a 15 but not quite so tall as an ali80). Mostly people use the tall ones.

    300 bar 12s are always like the tall ones (ie same diameter as a 10 or ali80) but a little bit taller and a lot heavier).

    There are a few variations by manufacturer too. Mostly you see Faber, but for DIR style twinsets other brands are popular and they are heavier and marginally narrower than Faber ones. Sometimes those, or similar, turn up as singles but they are not usual.
     
  8. Bob DBF

    Bob DBF Solo Diver

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    Location: NorCal
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    The Faber MP 120 sounds closer to the 12l 300 bar, being -7# empty and a 3498# fill pressure with a + rating. This may be what gives rise to the thought they are the same tank, filling specs for both markets.


    Bob
     
  9. Storker

    Storker Divemaster

    # of Dives: 100 - 199
    Location: close to a Hell which occasionally freezes over
    14,231
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    300 bar is 4350 psi. 3500 psi is about 240 bar, not far from Euro standard 232 bar (3365 psi).

    If you have 120 cu.ft (3400 surface liters) at 240 bar, your tank's water volume is 14L. 15L water volume at 225 bar (3260 psi) is also 3400 surface liters (120 cu.ft).
     
  10. T Mogle

    T Mogle Solo Diver

    # of Dives: 25 - 49
    Location: United Kingdom
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    Interesting discussion.

    I am currently renting tanks, 12L steel, 232 BAR. I have done the math, and think my first owned tank will be 10l 300 BAR, long tank. Reading the comments is not making it easier to choose.
    + It holds more gas than a 12x232. For about the same weight.
    + Might able to drop some weight off my belt? Most likely not.
    - Told that most fill stations are only able to give you 270 BAR at most. Still more than a 12x232.
    - No need to be concerned about overfilling.

    My local dive shop keeps telling me, as a new diver I will be happier with the standard 12x232, steel. As a new diver I need air, more is better.
     

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