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Thread: How scrubbers work, and why we do scrubber cyling:

  1. #1
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    How scrubbers work, and why we do scrubber cyling:

    hi all,

    as there seems to be some mis-understanding on how scrubbers work, and why cycling can have clear advantages:

    here some pure data from one typical dive:


    system 1:
    dual scrubber, each 1.35kg, 15° warm water, low-medium working dive: scrubber breaks through (CE limit) after around 6 hours)

    system 2:
    single scrubber same total volume, 2.7kg
    same diving conditions (althow the single scrubber will break through a bit faster under the same conditions, but for ease of comparison, we neglect this)


    A: % of time till real break through (5 mbar PPCO2)
    B: % sorb saturation of first scrubber (of dual system)
    C: % sorb saturation of second scrubber (of dual system)
    D: % sorb saturation of total scrubber in case of single scrubber



    A B C D
    % % % %
    20 28 0 14
    40 57 1 29
    60 78 5 41
    70 83 11 47
    80 87 20 53
    90 90 31 60
    100 92 43 67




    now you're free to choose at what % of time till break through (A: safety margin) you will either dump your complete scrubber (if you have a single scrubber), or only dump the first scrubber (if you have a dual scrubber)

    now calculate how much time you dive/kg sorb, with the same safety margin (dumping or cycling at the same moment)


    depending on temperature, and measuring the real data during the dive, the rMS forces to cycle between 60 and 75% of real break-through time

    for the dual scrubber system, the sorb you dump is saturated for about 80%

    for the single scrubber at the same time, the sorb is saturated for around 43% ..

    this should make things clear..

    ps: for cold water, or harder working, the saturation percentages are even lower!
    www.rEvo-rebreathers.com
    ...."Yes you have to pre-breathe to activate the scrubber sorb, anyone who says different doesn't know what they are talking about!"...
    .... to get more accurate CO2 injection in the breathing machine we put 2 mass flow controllers in series ...
    .... The noise is a few tens of nano-volts, so DL were able to reduce the output voltage ...
    .... radial scrubbers give longer dwell time than axials...
    .... the earth is flat and ...

  2. #2
    Doing What Works jcook is an unknown quantity at this point jcook's Avatar
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    Re: How scrubbers work, and why we do scrubber cyling:

    Call me an idiot, but you stated at 92% and 43% of your dual system, you will have total breakthrough? So by this reasoning, you got breakthrough on your first scrubber at 43%? That doesn't seem like scrubbers are designed very well to accept breakthrough at 43%. With simple math, the average % of the dual scrubber's breakthrough is 67.5%, which is the same as the single scrubber. I don't see why these dual scrubbers are so much better than a single one, other than to save a little sorb. I just fail to see why saving a few dollars in sorb is so important to you and your followers. Again, may be that american isn't your first language and I just don't understand.

    Also I would like to know what kind of single scrubber you tested, as you didn't state it. Was it a radial or axial? Since that will affect the breakthrough quite differently.
    Last edited by jcook; 10th July 2012 at 15:36.

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    Re: How scrubbers work, and why we do scrubber cyling:

    Quote Originally Posted by jcook  View Original Post
    Call me an idiot, but you stated at 92% and 43% of your dual system, you will have total breakthrough? So by this reasoning, you got breakthrough on your first scrubber at 43%? That doesn't seem like scrubbers are designed very well to accept breakthrough at 43%. Again, may be that american isn't your first language and I just don't understand.

    Also I would like to know what kind of single scrubber you tested, as you didn't state it. Was it a radial or axial? Since that will affect the breakthrough quite differently.
    let's see if for other readers my text is clear then we can see if it's my English (since when is american a language..)

    also, it looks like you don't understand scrubbers quite well: it is a fact (easely to measure, test, proof), that on a single scrubber, axial or radial, that does not matter, in cold water, you will have break through before your sorb is saturated for 50%


    so to clear up a bit (I hope), for this typical dive, there was break through when the exhale scrubber was saturated for 92% and the inhale scrubber for 43%

    the single 2.7kg example is an axial model
    www.rEvo-rebreathers.com
    ...."Yes you have to pre-breathe to activate the scrubber sorb, anyone who says different doesn't know what they are talking about!"...
    .... to get more accurate CO2 injection in the breathing machine we put 2 mass flow controllers in series ...
    .... The noise is a few tens of nano-volts, so DL were able to reduce the output voltage ...
    .... radial scrubbers give longer dwell time than axials...
    .... the earth is flat and ...

  4. #4
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    Re: How scrubbers work, and why we do scrubber cyling:

    Quote Originally Posted by jcook  View Original Post
    you stated at 92% and 43% of your dual system, you will have total breakthrough? So by this reasoning, you got breakthrough on your first scrubber at 43%?
    Dual scrubber: ~(92%+43%)/2 = 67%
    Single scrubber: 67%

    If you split the single scrubber in half, the bottom half closest to the gas would have been 92% consumed and the top half 42% consumed. Paul states you would perform a cycle well before you get to this saturation point. Effectively at 67%, either dual or single are exhausted and no cycle can be performed.

    Using 60% as cycle time -
    Dual scrubber: ~(78%+5%)/2 = 41%
    Single scrubber: 41%
    Dual scrubber following cycle: ~(5%+0%)/2 = 2.5%
    Last edited by DwayneJ; 10th July 2012 at 15:45.

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    Doing What Works jcook is an unknown quantity at this point jcook's Avatar
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    Re: How scrubbers work, and why we do scrubber cyling:

    Quote Originally Posted by paulraymaekers  View Original Post
    also, it looks like you don't understand scrubbers quite well: it is a fact (easely to measure, test, proof), that on a single scrubber, axial or radial, that does not matter, in cold water, you will have break through before your sorb is saturated for 50%
    Actually I do. I do know that you technically get a small amount of breakthrough on a scrubber with each breath, so even before the total sorb has been saturated to 50%. It also depends on the type of sorb and the external amount of surface area on the sorb for the amount that can be scrubbed with each breath.

    You don't need to try and belittle me Paul, it's in bad taste.
    Last edited by jcook; 10th July 2012 at 15:45.

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    Re: How scrubbers work, and why we do scrubber cyling:

    euh, you change your post faster then I can reply

    few answers:

    - using the same safety margins, dual scrubber systems use only half the amount of sorb (not to hard to find places in the world where you pay >$15 per kilo, or where you have to take it with you when traveling)
    - applying cycling using the same saturation as criteria, gives fare increased safety margins on dual scrubbers
    - likelihood of channeling is lower on dual scrubbers
    - dual scrubbers gives lower profile
    ...
    www.rEvo-rebreathers.com
    ...."Yes you have to pre-breathe to activate the scrubber sorb, anyone who says different doesn't know what they are talking about!"...
    .... to get more accurate CO2 injection in the breathing machine we put 2 mass flow controllers in series ...
    .... The noise is a few tens of nano-volts, so DL were able to reduce the output voltage ...
    .... radial scrubbers give longer dwell time than axials...
    .... the earth is flat and ...

  7. #7
    rEvo's daddy
    paulraymaekers has a reputation beyond repute paulraymaekers has a reputation beyond repute paulraymaekers has a reputation beyond repute paulraymaekers has a reputation beyond repute paulraymaekers has a reputation beyond repute paulraymaekers has a reputation beyond repute paulraymaekers has a reputation beyond repute paulraymaekers has a reputation beyond repute paulraymaekers has a reputation beyond repute paulraymaekers has a reputation beyond repute paulraymaekers has a reputation beyond repute paulraymaekers's Avatar
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    Re: How scrubbers work, and why we do scrubber cyling:

    Quote Originally Posted by jcook  View Original Post
    ....Call me an idiot, but you stated at 92% and 43% of your dual system, you will have total breakthrough? So by this reasoning, you got breakthrough on your first scrubber at 43%?...


    ...You don't need to try and belittle me Paul, it's in bad taste.
    I don't think this is anything about bad taste or belittle..

    just first read your post, find the errors in it, and come back

    it also seems that you reply, and jump to conclusions, without knowing how the rEvo dual scrubber works
    www.rEvo-rebreathers.com
    ...."Yes you have to pre-breathe to activate the scrubber sorb, anyone who says different doesn't know what they are talking about!"...
    .... to get more accurate CO2 injection in the breathing machine we put 2 mass flow controllers in series ...
    .... The noise is a few tens of nano-volts, so DL were able to reduce the output voltage ...
    .... radial scrubbers give longer dwell time than axials...
    .... the earth is flat and ...

  8. #8
    Doing What Works jcook is an unknown quantity at this point jcook's Avatar
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    Re: How scrubbers work, and why we do scrubber cyling:

    Quote Originally Posted by paulraymaekers  View Original Post
    I don't think this is anything about bad taste or belittle..

    just first read your post, find the errors in it, and come back

    it also seems that you reply, and jump to conclusions, without knowing how the rEvo dual scrubber works
    All I did was ask a question about your math, the scrubber design, and how you came to those conclusions. You don't need to be a dick to me about asking a few questions about your system. Plus you never answered my original question, does the first scrubber in your system break though at 43%?

  9. #9
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    Re: How scrubbers work, and why we do scrubber cyling:

    Quote Originally Posted by jcook  View Original Post
    All I did was ask a question about your math, the scrubber design, and how you came to those conclusions. You don't need to be a dick to me about asking a few questions about your system. Plus you never answered my original question, does the first scrubber in your system break though at 43%?
    Its the first scrubber at 97% and the second scrubber at 43% that breaks through like the single scrubber at 67%. Dual or single are fully exhausted and the dual cannot/should not be cycled. A split scrubber works identical to the single scrubber.

    The benefit of cycling occurs before the scrubber stack is saturated.

    Give Paul the benefit of the doubt - the Europeans speak multiple languages and they can come off blunt/direct.
    Last edited by DwayneJ; 10th July 2012 at 16:14.

  10. #10
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    Re: How scrubbers work, and why we do scrubber cyling:

    Quote Originally Posted by jcook  View Original Post
    All I did was ask a question about your math, the scrubber design, and how you came to those conclusions. You don't need to be a dick to me about asking a few questions about your system. Plus you never answered my original question, does the first scrubber in your system break though at 43%?
    so I'm a dick when I point to you that you jump to conclusions after making wrong assumptions? well well, bad taste...

    so I'll even be nice, and answer on this one:

    1 wrong assumption:

    So by this reasoning, you got breakthrough on your first scrubber at 43%

    2 my answer: no: there is break through when the first scrubber is saturated for 92%
    www.rEvo-rebreathers.com
    ...."Yes you have to pre-breathe to activate the scrubber sorb, anyone who says different doesn't know what they are talking about!"...
    .... to get more accurate CO2 injection in the breathing machine we put 2 mass flow controllers in series ...
    .... The noise is a few tens of nano-volts, so DL were able to reduce the output voltage ...
    .... radial scrubbers give longer dwell time than axials...
    .... the earth is flat and ...

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