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How much air does an LP85 hold at 2400 PSI?

Discussion in 'Tanks, Valves and Bands' started by CaveSloth, Sep 23, 2019.

  1. JohnnyC

    JohnnyC PADI Pro

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    An LP85 will hold 85cuft of gas at 2640 psi. At 2400 psi it will hold roughly 77cuft of gas. At 3600 it will hold roughly 115cuft of gas.

    Your latest hydro says you can only fill your tanks to 2400 psi (no + rating). If they are actually LP85's as you have suggested, they will hold 77cuft of gas at rated pressure.

    I'm not sure where the confusion is coming from. This was answered at the beginning of the thread.

    A + sign means it is rated for 10% overfill from its stamped rating, and must be renewed at hydro. In your case, since your tanks are rated for 2400 psi with a + when it was made, they could be filled to 2640 psi. Since subsequent hydros did not receive the + rating, the rated pressure is only 2400 psi. And the rated capacity is based on filling to this +10% overfill rating. A + sign does not mean that a tank holds more at the same pressure.
     
    Bob DBF likes this.
  2. CaveSloth

    CaveSloth Manta Ray

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    I measured the tank diameter twice and got the same number both times: 22.25 " Divide that by 3.14 and you get 7.09" diameter.
     
  3. CaveSloth

    CaveSloth Manta Ray

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    OK, so it sounds like a + sign or not has no effect on how much it holds at a given pressure. Good to know.

    Can someone positively confirm that the plus sign beneath my hydro stamp either does or doesn't have meaning?
     
  4. tursiops

    tursiops Marine Scientist and Master Instructor ScubaBoard Supporter

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    No, and No, to your first paragraph questions.

    The plus sign has to be reapplied at each hydro. It was not, so it no longer exists.
    It only means you can put 10% more pressure (2640 vs 2400) into the tank, thus 10% more volume (85 vs 77).

    If they are "85"s, they now function as 77s.
     
    rjack321 likes this.
  5. CaveSloth

    CaveSloth Manta Ray

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    Ok, thanks for finally answering my questions!
     
  6. rjack321

    rjack321 ScubaBoard Supporter ScubaBoard Supporter

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    How would a mark on the outside change how much gas was on the inside? If there's 2400psi in the tank with a + on the outside its 77cf. In there's 2400psi in that tank with no + on the outside its still 77cf.
     
  7. CaveSloth

    CaveSloth Manta Ray

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    It makes sense to me now, thanks.
     
    rjack321 likes this.
  8. CaveSloth

    CaveSloth Manta Ray

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    LOL OK GUYS! I get it! I am a dumbass! Thanks for rubbing it in. I was stupid and I had no idea what the plus sign meant. Maybe I thought it was a bad thing like it meant you had to fill it to a higher pressure to get the same amount of air in. I have no idea what goes on inside my head it's all dusty in there.
     
  9. Lorenzoid

    Lorenzoid idling in neutral buoyancy ScubaBoard Supporter

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    No worries. As they say, the only dumb question is that one you decided not to ask.

    Be careful out there in the caverns, dude. You should be able to look at your SPG and figure out how much air (in cubic feet) you have in your tank.
     
  10. tursiops

    tursiops Marine Scientist and Master Instructor ScubaBoard Supporter

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    The Faber specs also show a 13 liter tank that is 7 inches in diameter and 184 bar WP. That would provide 2382 liter when full, or 84.5 cuft. Is the tank length 26 inches (not incl the valve)?
     
    CaveSloth likes this.

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