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Thread: What part is he talking about?

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    What part is he talking about?

    I came across this when researching an RB80 purchase. What is the component he's referring to? And how genuine is this concern?

    "The RB80 has a failure mode that will prioduce NO physical warning. Hypoxia is nasty in that most people do not realise anything is up and are incapable of doing anything even if they do (that includes bailing out). Whats worse is that in most passive systems (including the RB80) the key componenet that can fail in this maner is a flexible membrane that is flexed every breath, is inside another component so not readily visible and inspectable and the unit will still pass positive and negative pressure checks if it has failed. You can dive without the monitor and just hope this component never fails or take the sensible option of fitting a O2 monitor."

  2. #2
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    Tom,

    He was referring to the mushroom valve on top of the small bellow responsible for releasing 1/10 of each breath.

    When part of the breath is released, the 2 "ADV" will activate on the next breath due to the smaller loop volume (while on constant depth) to replenish with new gas and keep the loop fiO2 near the fiO2 of the tank.

    That's the basic functionality of the PVR/RB-80/EDO system.

    Since this small bellow is inside the larger bellow, you can't physically see it and inspect its function VISUALLY. However, if you are trained properly and have a attentive dive buddy, it should be no problem to detect if it has failed and you are not releasing any gas (no bubble) during the pre-dive check and during the dive.

    You should be able to tell that gas is being released and added with each breath by a few things:
    • bubbles released from behind when you inhaled
    • toward the end of your inhalation cycle, you should hear the sound of short gas injection to make up the lost volume due to gas released
    If the mushroom had failed to close, no gas will be dumped on the inhalation breath and you will keep rebreathing the same loop volume over until the loop gas becomes hypoxic and, most likely, you will pass out and drown if you don't have a buddy to verify that you are releasing gas or you being able to do so yourself.

    As mentioned, it could be easily prevented by proper pre-dive check and in-water monitoring similar to monitoring a PO2 meter on a CCR.

    Of course, you could also mount a single sensor in the loop and monitor it for the PO2 to have an added safety margin as well.

  3. #3
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    While the RB80 isn't failsafe you should be able to hear the gas injection, in addition to visually confirming the ejection of the gas from the inner bellows.

    There is a very good teardown of the RB80 where you can see all the inner bits and pieces, including said valve . Just select SCR teardown from the main menue.

    This valve, by the way, was damaged in the double-EDO-04 rig that was involved in a fatal accident a while ago. The diver was reportedly new to the unit, solo, without proper training, and did his final dive in very shallow water IIRC.
    Should be avoidable with correct pre-dive and diving procedures.

  4. #4
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    It is possible to verify it is working during assembly, Michael from STDE showed me how when I was thinking of buying an EDO-04 (I assume the RB80 will be similar). You put a little water in the bulkhead and then work the bellows manually. If the valve is working then the water gets sucked into the bellows and pumped out the dump valve. If it isn't then the water will either drain straight away without working the bellows if it has failed open or not at all if failed closed. In use, not only can you hear gas being dumped and added but you also feel the addition valves fire on the inhale stroke.

    However if you have the wrong gas plugged in during ascent then you will die even with a fully functioning rebreather unless you have an O2 monitor. The ppO2 decay can be quite large when going up.

    Cheers,

    Stuart

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    Quote Originally Posted by lizardland
    However if you have the wrong gas plugged in during ascent then you will die even with a fully functioning rebreather unless you have an O2 monitor.
    Stuart,

    Re-read the part about proper training...

    There isn't much of a difference between plugging a wrong gas on RB-80 and switching/breathing a wrong gas on OC. Proper training and buddy-verifying protocol should eliminate this issue.

    Besides, even if you don't go hypoxic, you will bend like a pretzels anyway...

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    Quote Originally Posted by decoweenie
    Stuart,

    Re-read the part about proper training...

    There isn't much of a difference between plugging a wrong gas on RB-80 and switching/breathing a wrong gas on OC. Proper training and buddy-verifying protocol should eliminate this issue.

    Besides, even if you don't go hypoxic, you will bend like a pretzels anyway...
    Hi Phi,

    as you know there is no training available for the EDO-04 or any of the other RB80 clones.

    Cheers,

    Stuart

  7. #7
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    Quote Originally Posted by lizardland
    as you know there is no training available for the EDO-04 or any of the other RB80 clones.
    More reason for anyone buying/diving one of these units to get some form of "training" thru mentorship or consult with those who have gone thru the PVR/RB-80 training.

    It is absolutely crazy to dive a RB without any form of "training", either official certification or mentorship learning from experienced divers.

    Some earlier KISS owners might disagree with me since no certification was required in the beginning, but I am sure they won't deny that they had done a lot of Internet research and/or reading training manual (i.e. self learning process).

    It is possible to self-learn as much as a structured course, but is not a guaranty since people have different perceptions when looking at the same material. And drawing the experience from a good instructor is very valuable as well.

  8. #8
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    Hi Phi,

    I'm not knocking it, I think it has a lot of merit. I dive a homebuilt RB afterall, where do I go for training? :)

    Cheers,

    Stuart

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    Quote Originally Posted by lizardland
    I'm not knocking it, I think it has a lot of merit. I dive a homebuilt RB afterall, where do I go for training? :)
    Since I have seen pictures of your homebuilt unit, I would suggest the local pub. so at least you will go out happy diving it...

  10. #10
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    I'm very hurt by that :)

    Or are you talking about the Yellow Bag of Death. In which case all comments are justified!

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