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  1. #21
    Established TDF Member
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    I change mine all in one go, think APD recommend this (and same batch). That said, I order three new cells, install one dive it & if OK repeat with next cell until all 3 replaced. That said, with the APD cells only lasting 4 - 6 months it's not really an issue at the moment.

    New units come with 3 new cells often from same batch!

  2. #22
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    Dupe
    Last edited by JPTaylor; 20-02-2013 at 10:45 AM.

  3. #23
    Purine hurts my feet Major Clanger's Avatar
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    Changing 02 Cells

    Quote Originally Posted by Stonybonytony View Post
    What struck me about Paul's paper, is that the risk of 3 of 5 cells failing in the simulation was 6 in a million. I can cope with 1 cell fail, no problem, and 2 is probably ok, though complicated in they were both on the shearwater and hence would affect automatic oxygen injection, but 3 and I wouldn't even have a trustable majority, and would effectively have no idea what the ppo2 was. At this point I would of course bail or at least go to scr mode depending where it was/ what I was doing. Though Sod's law it would happen right in the middle of some other crisis when brain is already busy dealing with something else.

    Anyhow, 6 in a million, 1 in 166,000, doesn't sound bad. But if I do 50 dives a year, then it's a 1 in 3,000 risk in any year. And if I dive for the next 25 years, then there's a 1 in 133 chance of experiencing a 3 cell failure at some point. Which to me starts too look much too much like "something that could happen".

    There is an apocryphal story about a Boeing executive who only flew on 4 engined planes. When asked why, he replied "because we don't make 6 engined planes"
    I'm not sure the likelihood of multiple cell failure increases the more years you dive, all things being equal and changes made within guidelines.

    As an aside, though with possibly some relevance to failure statistics, I read somewhere that the likelihood of a spitfire pilot getting shot down during WW2 was the same each flight no matter how often they'd flown.
    GaryL

  4. #24
    Nick D Zero-Viz's Avatar
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    Quote Originally Posted by Stonybonytony View Post

    I read recently, and I imagine it was on here or the other place, of a 3 cell rebreather where 2 cells failed simultaneously, and the two that failed were closest to each other and hence out voted the third good cell.
    I've seen this happen to a Sentinel on a dive. The dil flush showed that it was two bad cells outvoting the one good one so they had to disable the two bad cells.

  5. #25
    Nick D Zero-Viz's Avatar
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    ...

  6. #26
    Charlie SoggyBottoms's Avatar
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    on the Vision:

    In the Dive Mode - Underwater Menu, when deeper than 1.2m, there is a useful “Cell Check” display which calculates what the ppO2 will be if you flush effectively at your current depth.
    The display on the left is the ppO2 should you flush with diluent and the display on the right is the ppO2 should you flush with oxygen.

    I thought this useful for quick checks on cells
    regards, Charlie

    charliesez http://tinyurl.com/bjjus8g

  7. #27
    Closed Account: User Requested nickb's Avatar
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    Quote Originally Posted by SoggyBottoms View Post
    on the Vision:

    In the Dive Mode - Underwater Menu, when deeper than 1.2m, there is a useful “Cell Check” display which calculates what the ppO2 will be if you flush effectively at your current depth.
    The display on the left is the ppO2 should you flush with diluent and the display on the right is the ppO2 should you flush with oxygen.

    I thought this useful for quick checks on cells
    The Predator also has a diluent F02 output available with a few presses on the right-hand button.

  8. #28
    Closed Account: User Requested nickb's Avatar
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    Quote Originally Posted by SoggyBottoms View Post
    on the Vision:

    In the Dive Mode - Underwater Menu, when deeper than 1.2m, there is a useful “Cell Check” display which calculates what the ppO2 will be if you flush effectively at your current depth.
    The display on the left is the ppO2 should you flush with diluent and the display on the right is the ppO2 should you flush with oxygen.

    I thought this useful for quick checks on cells
    The Shearwater Predator also has a diluent F02 output available with a few presses of the right-hand button.

  9. #29
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    The day will come when as you get to 6msw to do a bubble check, the depth sensor twig's where you are, and instructs the solenoids to fire (oop's wrong word ) O2 across the cells and cross check that they read 1.6, all in the blink of an eye !
    If it passes this linearity check it automatically makes the set point 1.3, but if it fails this check, drops the set point to 1.2.

    Oh, it already does on the Mk6 :middlefinger:

  10. #30
    Moderator GLOC's Avatar
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    Changing 02 Cells

    Neil, I do believe that there are some great innovations on MkIV and when the O2 cell presentation was given at RF3.0 there were certainly a few people asking why isn't cell/gas/depth sensor validation taking place using dil and or O2.

    Regards
    Gareth

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