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Thread: Wow! Meg design - dont know if I like this

  1. #1
    RBW Member Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike's Avatar
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    Wow! Meg design - dont know if I like this

    I have been tearing apart a meg today and Ive noticed something I didnt think of before.


    The cells are screwed in from the exhale side and the sensor faces are on the inhale side.

    So the cells have to seal into the cell holder in order to stop bypass (from inhale direct to exhale missing the scrubber)


    Even though I didnt like the cell being a 'seal' or the fact there would be a temp and gas difference across the cell I figured well the sensor thread is a good fit in its holder so the seal would be good enough.

    But then I thought about the 3 most recent cell failures Ive had. As reported before I had three cells fall apart in use in an unusal way where the body of the cell parted from the faceplate (bit that screws into the holder) Now Im thinking what would happen if that had happen to me on a Meg??? There effectively would be a direct hole from the inhale to the exhale side of the loop!!

    hmmm.

    Not sure thats a good design. I dont like the idea of the glue that holds the cell to the cells faceplate being the seal between inale and exhale. A bypass there I guess could be very nasty.

  2. #2
    RBW Member Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike's Avatar
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    Re: Wow! Meg design - dont know if I like this

    something like this.

    I guess as well as temp there is also a small pressure differential across the sensors too....


    hmmm

    I thought for accurate sensing it was important that the cell face and body (circuitry) saw exactly the same pressure - or did I imagine that? I seem to recall something about not blocking the vent holes on top of teleydynes for this reason.??


    With the sensor body being colder than the sensor face (the former exposed to cold injected O2 and exhaled gas) do Meg divers see much condensation on the cell faces??
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    Last edited by Drmike; 27th April 2007 at 10:59.

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    Re: Wow! Meg design - dont know if I like this

    Mike,

    Interesting observation. I look forward to other responses on this. I specifically remember when AP was going through sensor issues and some of them were attributed to back pressure on the cells due to a venting hole in the cell curcuit board either being non existiant or blocked with glue on the "Classic". Regardless is does seem to leave a potential weak spot in the loop like a heart "PFO" waiting to happen.

    Dive Safe

    Mark

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    Re: Wow! Meg design - dont know if I like this

    DrMike

    Can you point me to your posts about the cells coming apart.;)

  5. #5
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    Re: Wow! Meg design - dont know if I like this

    Hi Mike

    I agree that this is a week area on the unit. During training students are show to perform a possitive and negative pressure test on the head that would expose an O-ring failure either on the cell or the base of the pod. What is more worrying is I have had meg divers through our facility that have not been shown how to do this, In my opinion its a vital pre dive check.

  6. #6
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    Re: Wow! Meg design - dont know if I like this

    Quote Originally Posted by tecdivertraining  View Original Post
    Hi Mike

    I agree that this is a week area on the unit. During training students are show to perform a possitive and negative pressure test on the head that would expose an O-ring failure either on the cell or the base of the pod. What is more worrying is I have had meg divers through our facility that have not been shown how to do this, In my opinion its a vital pre dive check.
    Matt,

    Should we be concerned that this would be putting undue stress on the cell face itself?

    Thanks

    Mark

  7. #7
    RBW Member Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike's Avatar
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    Re: Wow! Meg design - dont know if I like this

    Quote Originally Posted by Paul Evans  View Original Post
    DrMike

    Can you point me to your posts about the cells coming apart.;)
    http://www.rebreatherworld.com/showthread.php?t=10944

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    RBW Member tecdivertraining is a name known to all tecdivertraining is a name known to all tecdivertraining is a name known to all tecdivertraining is a name known to all tecdivertraining is a name known to all tecdivertraining is a name known to all tecdivertraining is a name known to all tecdivertraining is a name known to all tecdivertraining is a name known to all tecdivertraining is a name known to all tecdivertraining is a name known to all tecdivertraining's Avatar
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    Re: Wow! Meg design - dont know if I like this

    Quote Originally Posted by diverklondike  View Original Post
    Matt,

    Should we be concerned that this would be putting undue stress on the cell face itself?

    Thanks

    Mark
    Mark

    I am more worried about CO2 by-passsing the scrubber via a failed oring or lose conection than stressing the cells.

  9. #9
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    Re: Wow! Meg design - dont know if I like this

    Quote Originally Posted by tecdivertraining  View Original Post
    Mark

    I am more worried about CO2 by-passsing the scrubber via a failed oring or lose conection than stressing the cells.
    Hey Matt hows things.

    My concern would be if a cell parts away from the faceplate as mine did. You would then have a big hole giving you a nasty bypass. If you look at how the cells are constructed theres just a thin line of silicon around the edge of the faceplate. Maybe I had a bad batch (ive never had it before) But the fact is it did happen to me - more than once so it is a possible failure - and given the Meg design I cant help but think it could be a very dangerous failure


    John I should have said 'tear down' rather than 'tear apart' LOL! :D Dont worry your baby is still in once piece :D
    Last edited by Drmike; 27th April 2007 at 12:18.

  10. #10
    Cheeky Monkey........... Paul Evans is a name known to all Paul Evans is a name known to all Paul Evans is a name known to all Paul Evans is a name known to all Paul Evans is a name known to all Paul Evans is a name known to all Paul Evans is a name known to all Paul Evans is a name known to all Paul Evans is a name known to all Paul Evans is a name known to all Paul Evans is a name known to all Paul Evans's Avatar
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    Re: Wow! Meg design - dont know if I like this

    Thanx for the link Drmike.

    As has been mentioned the Pos / Neg test should spot this.

    It was stressed by my instructor (Dennis Vessey)

    In my very limited experiance Moisture does build up on the cell faces. Hence the training to make sure the head is removed and dryed over night. I cannot coment on the moisture build up on other units as I have never seen it:o so do not have a comparison to measure by.

    The cells that you had that came apart are not the ones That are recomended by ISC.

    But you are correct, Structural faluire of the cell itself will lead to a bypass.
    I have not heard about this ever happening with a meg. That does not preclude the possibility. Any futher info from anybody would be very helpfull.

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