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Thread: O2 cell co2 bypass potential?

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    Shearwater Copis Diver Gill Envy has a reputation beyond repute Gill Envy has a reputation beyond repute Gill Envy has a reputation beyond repute Gill Envy has a reputation beyond repute Gill Envy has a reputation beyond repute Gill Envy has a reputation beyond repute Gill Envy has a reputation beyond repute Gill Envy has a reputation beyond repute Gill Envy has a reputation beyond repute Gill Envy has a reputation beyond repute Gill Envy has a reputation beyond repute Gill Envy's Avatar
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    O2 cell co2 bypass potential?

    Greetings ISC folks, some grave concerns have been brought to light that a structural failure of an o2 sensor could lead to co2 bypass in the head. While I've dismantled a retired o2 sensor to see if I could create this problem and found it to quite difficult to reproduce with the batch of cells I have, it does bring up the question that tolerances in manufacturing uniformity or prolonged exposure to caustic moist environments could lead to the tape and housing of the cell to part below the membrane without apparent cause, creating a path of lesser resistance for exhaled air to bypass the scrubber.

    Does ISC have any comment on this? Any recommendations for ways to be extra, extra sure this will not happen, as I could see, however rare it might be, that such an occurance would create a sudden and unintuitive life threatening emergency. any suggestions would be greatly appreciated. It seems to me that the easiest precaution would be to find some way of further sealing the two end housing caps of the sensors together. It seems that this issue should ultimately be addressed by the cell manufacturer. A vulcanizing product or plastic solder might just do the trick. your consideration is greatly appreciated.

    Sincerely,

    Gill Envy

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    Re: O2 cell co2 bypass potential?

    Quote Originally Posted by Gill Envy  View Original Post
    Greetings ISC folks, some grave concerns have been brought to light that a structural failure of an o2 sensor could lead to co2 bypass in the head. While I've dismantled a retired o2 sensor to see if I could create this problem and found it to quite difficult to reproduce with the batch of cells I have, it does bring up the question that tolerances in manufacturing uniformity or prolonged exposure to caustic moist environments could lead to the tape and housing of the cell to part below the membrane without apparent cause, creating a path of lesser resistance for exhaled air to bypass the scrubber.

    Does ISC have any comment on this? Any recommendations for ways to be extra, extra sure this will not happen, as I could see, however rare it might be, that such an occurance would create a sudden and unintuitive life threatening emergency. any suggestions would be greatly appreciated. It seems to me that the easiest precaution would be to find some way of further sealing the two end housing caps of the sensors together. It seems that this issue should ultimately be addressed by the cell manufacturer. A vulcanizing product or plastic solder might just do the trick. your consideration is greatly appreciated.

    Sincerely,
    I was directed by a friend to this thread, from over a year ago, is the problem brought up still an issue for the meg, has it been resolved?

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    Re: O2 cell co2 bypass potential?

    This was a theory... a theory based on common sence, and yes if you look at the design its theoreticly possible,

    but it need to be pointed out that ITS NEVER ACTUALLY HAPPED. and I personally have tried to pull apart a Teledyne R-22D.. and I gave up...

    They are fused pretty frigin well...


    BUT I AM NOT AN EXPERT.....
    Monkey Diver Inc.
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    Re: O2 cell co2 bypass potential?

    Thanks Monkey, I am no expert either, the opposite, just trying to find out as much as possible about strenghts and weaknesses of the meg, things I'll address in a course with the trainer, to see what he says

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    Hammerhead CCR diverklondike has a reputation beyond repute diverklondike has a reputation beyond repute diverklondike has a reputation beyond repute diverklondike has a reputation beyond repute diverklondike has a reputation beyond repute diverklondike has a reputation beyond repute diverklondike has a reputation beyond repute diverklondike has a reputation beyond repute diverklondike has a reputation beyond repute diverklondike has a reputation beyond repute diverklondike has a reputation beyond repute diverklondike's Avatar
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    Re: O2 cell co2 bypass potential?

    Do a couple searches accross some of the old threads and it has been discussed at length... The net is that this issue exists with several units and it does happen....

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    Re: O2 cell co2 bypass potential?

    Do a pos and neg test on your head prior to every dive; that way even if this was to happen you'd notice before the dive. The odds of it happening are practically zero. The odds of it happening *during* a dive....?

    I only see it as a risk after disturbing the cells - i.e after unscrewing them for some reason (replacing, sticking in a cell checker etc).

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    Re: O2 cell co2 bypass potential?

    Quote Originally Posted by diverklondike  View Original Post
    Do a couple searches accross some of the old threads and it has been discussed at length... The net is that this issue exists with several units and it does happen....
    That's nice to know...just for some peace of mind...I had never heard of this, just some more things to worry about

  8. #8
    Shearwater Copis Diver Gill Envy has a reputation beyond repute Gill Envy has a reputation beyond repute Gill Envy has a reputation beyond repute Gill Envy has a reputation beyond repute Gill Envy has a reputation beyond repute Gill Envy has a reputation beyond repute Gill Envy has a reputation beyond repute Gill Envy has a reputation beyond repute Gill Envy has a reputation beyond repute Gill Envy has a reputation beyond repute Gill Envy has a reputation beyond repute Gill Envy's Avatar
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    Re: O2 cell co2 bypass potential?

    a pos/neg test does nothing to detect/prevent this, as an internal leak of this nature would not cause a failure of pos/neg test. the likelyhood of a cell failure of this type is quite remote. Dr Mikes post on the subject referenced cells that came apart easily... it would appear that this design issues has been addressed, as the cells available now are pretty robust.

    A similar and very real danger remains though, and everyone with a meg needs to keep an eye on it, the cells can back out of their threads, and if not installed all the way could conceivably provide a way for co2 bypass. the conclusion I came to was that a simple inspection of the cells to assure integrity and to assure they are securely screwed in is adequate to prevent this.

    While where are on the subject, it's worth noting that the "O" rings in the carriage can come out of their seat easily... special care is needed to assure this does not happen during assemply of the head as it could provided a path for breakthrough.

    g




    Quote Originally Posted by Rob Dobson  View Original Post
    Do a pos and neg test on your head prior to every dive; that way even if this was to happen you'd notice before the dive. The odds of it happening are practically zero. The odds of it happening *during* a dive....?

    I only see it as a risk after disturbing the cells - i.e after unscrewing them for some reason (replacing, sticking in a cell checker etc).
    Last edited by Gill Envy; 31st July 2009 at 16:04.

    Gill Envy

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    Re: O2 cell co2 bypass potential?

    Quote Originally Posted by Monkey  View Original Post
    This was a theory... a theory based on common sence, and yes if you look at the design its theoreticly possible,

    but it need to be pointed out that ITS NEVER ACTUALLY HAPPED. and I personally have tried to pull apart a Teledyne R-22D.. and I gave up...

    They are fused pretty frigin well...


    BUT I AM NOT AN EXPERT.....
    Monkey,
    I am pretty sure the were taking about the internal section leaking.
    It did happen to me one of my cells. After it went bad, I blew threw the membrane side and to my astonishment I was able to blow through it.
    It was a small amount and ISC has a cover over the connection side, so i think the risk is minimal. I think (and I am not an expert either) the sensor will show bad if there is a leak. checking the gasket under the carriage is something I do not see many people do.
    BTW. Monkey You were suppose to drop off 2 sensors.

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    Re: O2 cell co2 bypass potential?

    Quote Originally Posted by Gill Envy  View Original Post
    a pos/neg test does nothing to detect/prevent this, as an internal leak of this nature would not cause a failure of pos/neg test. the likelyhood of a cell failure of this type is quite remote. While where are on the subject, it's worth noting that the "O" rings in the carriage can come out of their seat easily... special care is needed to assure this does not happen during assemply of the head as it could provided a path for breakthrough.

    g
    A pos/neg test of the head only would detect this. Meaning that if you seal the hole on the top of the head and the hole on the bottom of the head that fits into the top of the scrubber and then provide a positive and negative pressure you would detect any major leaks in or out of that air space (which contains the cell faces and the O rings). I do this each time I change the scrubber and at the same time I check the calibration since I am using the calibration kit which contains caps to seal the holes on the top and the bottom.

    John

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