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Cave Fills on LP tanks

Discussion in 'Technical Diving Specialties' started by ScubaFeenD, Oct 15, 2010.

  1. ScubaFeenD

    ScubaFeenD Marine Scientist

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    I am looking to get a set of double tanks. I have been throwing around the idea of double 80s, or double hp100s, but recently i have even been considering double lp104s or 108s.

    Can anyone with experience, tell me more about cave fills. I realize that if I pump each lp tank to 3000 or 3400psi i wil get a boat load more gas, but can someone with experience and knowledge in the area specifically comment on the effects on the tank when you cave fill? Are there any safety concerns? Can the steel really handle it?

    Thanks
     
  2. Cave Diver

    Cave Diver Divemaster

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    I won't comment on how high my LP112's have been pumped to before, but I can tell you that they have spent most of their almost 10 year life being overfilled to 3300+

    It's a pretty common practice in cave country. Elsewhere, not necessarily so much.
     
    Rvbcave and KWS like this.
  3. PfcAJ

    PfcAJ Orca

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    I can't recall a single incident from this practice. I'm sure there is some theoretical worry about it, but in reality, it seems to be fine.

    That said, if you don't do your own fills and you don't live in North Florida, getting a 3000psi+ fill is going to be tough.

    What kind of diving are you planning on doing? Just for comparison, al80 doubles with a stage is almost as much as cave filled 104s/108s.
     
  4. ScubaFeenD

    ScubaFeenD Marine Scientist

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    Yea, I recognize that. I am just hoping to buy one set of tanks that can take me where I want to go in the future. Currently, I am heavily favoring getting a set of aluminums and using the saving to get a set stages (40s and 80s). I am just trying to weigh all my options appropriately.
     
  5. Rhone Man

    Rhone Man Divemaster

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    I bought a (fairly old) set of LP 72s, and everyone uses Aluminium in this part of the world, so whether I like it or not, I get fills to 3,100 psi whenever I take them in.

    Haven't blown up yet is all I can say. I kind of like diving "88s".
     
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  6. TSandM

    TSandM Missed and loved by many. Rest in Peace

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    Well, if you are planning on getting into technical diving, I will GUARANTEE that you will end up with more than one set of doubles. Staring at the ones that have just the wrong mix for the dive you want to that weekend gets very old. So I would highly recommend buying a set of doubles that you a) can afford b) can carry and c) will work for the dives you'll be doing in the next six months to a year. Worry about what you'll need for dives beyond that time frame when you get there. You WILL end up with more than one set, anyway.
     
  7. ucfdiver

    ucfdiver DIR Practitioner

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    I see no reason to buy LP tanks unless you get a great deal used. They are a pain to get filled to high pressures in most places, and aren't a whole lot cheaper. But then again, I wouldn't get LP104's for boat diving unless I was doing some massive dives. Even for cave diving I've found that LP85's and a stage can take me further in high flow than 104's
     
  8. Cave Diver

    Cave Diver Divemaster

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    People use double 80's for all sorts of things, from wreck to cave to quarry. The beauty of the 80's is they are versatile. You can double them and do a tech dive, add stages as necessary. You can break them apart to use as singles or as stages if you decide to get steels later. They also balance out nicer if your diving wet.
     
  9. Superlyte27

    Superlyte27 Cave Instructor

    # of Dives: 5,000 - ∞
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    But, to answer your question about filling...
    OMS used to have in their sales literature "Guaranteed for 10,000 Fills at 4000psi". This was right on the paperwork for LP85's and probably 95's and 104's. I never bought 95's or 104's but I remember thinking, wow, it's going to be a while before I get 10,000 fills on a set of tanks.

    I don't know of a single rupture from overfilling an LP tank that was in current hydro and vip. For that matter, I don't know of a single rupture from an LP 85, 95, 104 or 121. I think I've heard of some from LP72's but I could be mistaken.

    To figure in how much more gas you can hold (over an AL80) lets choose an LP85.
    An AL80 holds 77.4cu' of air at 3000psi. An LP85 holds 85cu' of air at 2400psi. These tanks are similar in size and weight on the surface.

    But, if we take an AL80 to 3600psi it holds 92.88cu' of gas 77.4/3000*3600.
    If we take an LP85 to 3600psi it holds 127.5cu' of gas. 85/2400*3600
    And with an LP85, you don't have to wear as much lead in the water, because it's more negative than the AL80.

    Now, does this do you any good at all if you can't get your LDS to fill to 3600? Maybe... but what if they won't fill your LP85 past 2640? That's a big jump in the cost of tanks for roughly the same amount of air that you can get in an AL80.
     
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  10. ScubaFeenD

    ScubaFeenD Marine Scientist

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    Yea, that is an excellent point.

    Thanks much for commenting on your experience. I think a lot of people, including my past self, used to think only in terms of how much gas tanks hold as opposed to also accounting for greater weight and drag.

    The versatility is definitely a plus.
     

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