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Cave Filling LP versus HP tanks

Discussion in 'Tanks, Valves & Bands' started by Compressor, Jun 23, 2018.

  1. MichaelMc

    MichaelMc Working toward Cenotes ScubaBoard Supporter

    # of Dives: 100 - 199
    Location: Berkeley, CA
    2,177
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    From the recent cave fill thread, this point of Charles above seems the key point. LP start out more conservative than HP.
     
    Last edited: Jun 23, 2018
  2. taimen

    taimen Rebreather Pilot

    # of Dives: 200 - 499
    Location: Europe
    850
    431
    That should be easy to confirm by comparing empty cylinder tare weights. If they indeed are identical cylinders they should weight the same.
    European 300bar cylinders are extremely heavy.
     
  3. Lobzilla

    Lobzilla Contributor

    # of Dives: 100 - 199
    Location: North Carolina, Maryland
    673
    167
    300 bar is ~4350 PSI. That's a lot, even in cave country. EU test pressure would be 6525 PSI (50% over service pressure) on these tanks whereas our 3AA 2400 PSI tanks get tested to 4000 PSI (5/3 of service pressure).

    Assuming that both tanks were designed so that their test pressure is less but somewhat close to the yield strength of the steel, our 3AA tanks would not survive the test pressure of the EU 300 bar tanks.

    I bet that the 300 bar tanks have substantially thicker walls and are therefore heavier that the LP (2400 PSI) and HP (3440 PSI) tanks we have here in the USA under 3AA (plus various exceptions). Our HP and LP tanks are pretty close in weight for similar outside dimension.
     
    Last edited: Jun 23, 2018
  4. Lobzilla

    Lobzilla Contributor

    # of Dives: 100 - 199
    Location: North Carolina, Maryland
    673
    167
    +1

    What is the test pressure for the 3442 PSI tanks and what exception do they fall under?
     
  5. Jonny Wishbone

    Jonny Wishbone Contributor

    # of Dives: I just don't log dives
    Location: West Central Florida
    339
    192
    curious. is there a chart or anyone has made up for LP tanks of what the CF of gas would be for different fill pressures? if so, could someone post...
     
  6. Charles2

    Charles2 Contributor

    # of Dives: I just don't log dives
    Location: Montgomery, Texas
    523
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    Test Pressure is stamped on the tank and for 3442 PSI tanks is 5250 psi.

    DOT exemption number for Faber is E-13488
     
  7. Lobzilla

    Lobzilla Contributor

    # of Dives: 100 - 199
    Location: North Carolina, Maryland
    673
    167
    Take the rated volume of the tank at service pressure, divide by service pressure, and multiply by desired pressure.

    I prefer to calculate for every tank a 'tank factor' that represents how many cubic feet every 100 PSI yield. That makes gas planning real easy.

    Tank Factor = Rated Volume / Rated Pressure * 100

    For Example: My AL80 doubles hold 154 cuft @ 3000 PSI and the tank factor comes out to 5.13 cuft/100PSI. I then call that 5 to make math easier.

    If my gauge shows 14 hundred PSI, I have at least 14 * 5 = 70 cuft left (71.87 to be precise).
     
    Last edited: Jun 23, 2018
    Jonny Wishbone likes this.
  8. taimen

    taimen Rebreather Pilot

    # of Dives: 200 - 499
    Location: Europe
    850
    431
    Yes, it is the rated service pressure.
    Most common new cylinders in my area are Eurocyliders (ECS) 12 liter 232 bar steels, that are 14 kg empty, 14,5 kg for the concave bottom version.
    ECS 12l 300 bar steel cylinder has 17,4 kg empty weight.
    232 bar cylinders are much more common.
     
  9. Storker

    Storker ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: 100 - 199
    Location: close to a Hell which occasionally freezes over
    17,157
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    So, your test pressure is 150% of service pressure. Just like it is on the right side of the pond.
     
    Charles2 likes this.
  10. Bob DBF

    Bob DBF Solo Diver

    # of Dives: I just don't log dives
    Location: NorCal
    10,658
    16,470
    Number one presumes that the rumor is true.

    Number two, even if they are of equal weight, it does not mean the alloy is the same. In addition I don't know the range of weight and size allowed in a run of tanks.


    Bob
     
    Last edited: Jun 23, 2018
    Lorenzoid likes this.

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