• Welcome to ScubaBoard

  1. Welcome to ScubaBoard, the world's largest scuba diving community. Registration is not required to read the forums, but we encourage you to join. Joining has its benefits and enables you to participate in the discussions.

    Benefits of registering include

    • Ability to post and comment on topics and discussions.
    • A Free photo gallery to share your dive photos with the world.
    • You can make this box go away

    Joining is quick and easy. Login or Register now by clicking on the button

Cave Fills on LP tanks

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

  1. northernone

    northernone Contributor Rest in Peace ScubaBoard Supporter

    # of Dives: 1,000 - 2,499
    Location: Currently: Cozumel, from Canada
    3,792
    3,409
    I won't cave fill aluminum. A good condition LP steel, I'll cave fill without hesitation. There's a low enough global rate of reported incidences that's it's practice that's within my risk tolerances.

    Filling strangers tanks, I'd be nervous but that's true regardless if it is to 2250 or 4000.

    Thanks for the update. I've suspected this from my o2 rebreather, I had first discounted it as sorb related irritation. Might be an interesting thread topic.

    Cameron
     
    Last edited: May 19, 2018
  2. LiteHedded

    LiteHedded Contributor

    4,075
    921
    On dives with a lot of o2 time I'll get out of the water having lost my voice with an irritated throat. Not always but sometimes
     
  3. Charles2

    Charles2 Contributor

    # of Dives: I just don't log dives
    Location: Montgomery, Texas
    523
    319
    I partially agree with you - I won't cave fill aluminum either. However, I don't agree that having a "low enough" global rate of reported incidences makes the overfilling of cylinders an acceptable practice. If both tanks were in "good condition" why would the filling of a 3AL cylinder to 90% of its test pressure be more of a risk than taking a 3AA cylinder to 90% of its test pressure?
     
  4. northernone

    northernone Contributor Rest in Peace ScubaBoard Supporter

    # of Dives: 1,000 - 2,499
    Location: Currently: Cozumel, from Canada
    3,792
    3,409
    Way up thread there's a nice metallurgy explanation of why over repeated cycles the aluminum fatigues more quickly (potentiality catastrophically) than steel.

    Cameron
     
    NAM001 likes this.
  5. Charles2

    Charles2 Contributor

    # of Dives: I just don't log dives
    Location: Montgomery, Texas
    523
    319
    If you are talking about post #51, it is a well written and informed post. As alluded to in that post; however, steel does have an "endurance limit". If the design stress is kept below that "endurance limit", steel can be cycled almost indefinitely without fatigue. Once that "endurance limit" is exceeded, steel no longer enjoys that same resistance to fatigue and will, in fact, fatigue in a similar fashion to aluminum. "Cave filling" of 3AA steel tanks increases the stress in the steel tanks to above that "endurance limit". I am sure that the metallurgists with the manufacturers could predict the number of cycles before failure at a 50% overfill of both 3AA and 3AL designed tanks. I suspect that we would all be surprised at that number and might even agree that the number is within our risk tolerance. We all pays our money and takes our chances.
     
    kelemvor likes this.
  6. KevinNM

    KevinNM DIR Practitioner

    3,030
    1,538
    Steel is really damn strong. I’d bet you are above 10,000 cycles before it fails hydro.
     
  7. АлександрД

    АлександрД Contributor

    # of Dives: 100 - 199
    Location: Moscow, Russia
    1,000
    1,844
    I know many people, who overfilling their tanks (steel), but most of them not over 10-20%...
    My opinion - tanks overfilling - it the same as Russian roulette
    Any overpressured 10-25 bar is the same, as another shell in revolver for Russian roulette...
    WP filled tank is like empty revolver, and 360 bar filled tank with wp200 is the same as full-charge load of six shooter
     
  8. victorzamora

    victorzamora Solo Diver

    3,041
    1,381
    Outside of the US, these matters seem to be pretty different. In the US, the "LP" tanks being discussed here are rated for ~180bar and being filled to ~245bar.

    The reason for the ratings has less to do with design and engineering than it does Government regulations. This was per a rep for one of the major manufacturers.
     
  9. АлександрД

    АлександрД Contributor

    # of Dives: 100 - 199
    Location: Moscow, Russia
    1,000
    1,844
    Ok, I understood....
    In States you are using S&W mod 60 (.38), instead of us with S&W mod 17 (.22) for this game...
     
    woodcarver likes this.
  10. Diver-Drex

    Diver-Drex Contributor

    # of Dives: 1,000 - 2,499
    Location: US east coast
    288
    147
    I’ve posted before about the code and regulatory issues with overfilling cylinders and won’t rehash that. But from a straight common sense perspective I just don’t get this. Someone please explain the thought process behind getting lp85s and overfilling them instead of getting hp100s? If you need 200cf of gas why don’t you just get the correct cylinders?
    Here are the dimensions to compare.
    Faber LP85 at +10% 7” dia., 26” height, 31lbs empty, -6.7lbs full buoyancy, neutral buoyancy empty given you 85cf.
    Faber FX100 7.25” dia., 25.4” height, 34lbs empty, -8.4lbs full buoyancy, -.6lbs empty buoyancy giving you 100cf.
    Over filling a LP85 has no advantage over a correctly filled 100. The weight and bouyancy differences are negligible at best. A quarter less diameter?
    For all of the talk of standards, doing things the right way and normalization of deviance I’m puzzled that many in the ‘cave community’ accept this practice.
     

Share This Page