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Flame rectification fooled

  1. Jul 27, 2017 #1
    A practical problem. A floor mounted boiler frp failed by cycling on and off rapidly with the main gas relay opening closing when there was no flame. This may be happening only when the igniter system is still hot.
    The main earthing is through the pilot gas tube, using an aluminum pipe with a brass olive into steel. There is considerable heat curve between the pipe and the steel electrode. Could a micro amp dc current be generating by the Seebeck effect to confuse the detection system?
     
  2. jcsd
  3. Jul 27, 2017 #2
    Could a micro amp DC current be generated? Absolutely.
    Could it confuse the detection system? I am thinking that you are talking about the flame detection system - but perhaps not. In any case, any product detection system should be well isolated from the affects of ground currents. So my guess would be "No".
    Of course, it would take a closer examination of the system to know with any certainty. But I really doubt it.
     
  4. Jul 27, 2017 #3
    Thanks Scott, I think unlikely, but replacing the controller doesn't fix it. It is stopping lockouts which I thought impossible. The issue is that the electrode would have a DC bias relative to ground. I don't know, the setup is mikeymouse, happens on several waterheaters and no engineer has yet found the reason. It is intermittent, maybe temperature related but passes every test on the manufacturers test lab..any other ideas?
     
  5. Jul 27, 2017 #4

    Tom.G

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    The operative words are bolded above. Follow-up your hunches. Any way of even temporarily connecting a wire across the aluminum-steel joint? Try disconnecting the sensor on a problematic device. Could be an intermittent open or ground in wiring to the sensors. Also check grounding of controllers. It could even be an issue with the power source. Or someone may even have decided to use the gas supply line as an electrical ground somewhere in the building.:nb)
     
  6. Jul 27, 2017 #5

    jim hardy

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    hmmm

    Flame rectification? New to me, just looked it up.

    http://www.achrnews.com/articles/98085-troubleshooting-a-flame-rectification-system
    has a couple good troubleshooting ideas...

    https://yorkcentraltechtalk.wordpress.com/2011/05/23/the-phenomenon-of-flame-rectification/ explains how it works (which i really needed)
    Sounds to me like it's looking for a flame that isn't there.
    Does the ignitor try to start one?
     
  7. Jul 28, 2017 #6
    Thank you for your ideas. The two earth returns are by the pilot and main gas pipes.
    The theory that the hot tri-metal junction is causing confusion in the rectification system seems to be correct. This morning:
    Test at cold..eveything OK. Run the burner 20 mins...test failure.
    Predict that the main gas pipe earthing is faulty. Cool and remove the burner and the holding screw is loose. Tighten and replace. This time at hot: no failure. The only difference is that the failure happens when the earthing is defaulted through the pilot's hot tri-metal junction.
    I was doubtful that this would be the case, but now 90% likely.
    The down side is that the securing screw will soon be loose again due to poor design.
    There are thousands of these units with this inherent weakness- the resulting cycling can override the lockout...boom!
     
  8. Jul 28, 2017 #7

    jim hardy

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    Sounds like good troubleshooting.

    Is their sales department aware of this ?

    When you're sure you're right
    - here's what i would do -
    Take a picture,
    go to internet and find the parent company
    click on "Investor Relations" then "Executive Team", find Chairman of the Board

    Send to him a letter in your own handwriting describing that problem
    tell him how you fixed yours with a work-around
    and that you await their corporate response particularly a retrofit kit to provide an improved and reliable earthing means..

    A video of the gas valve cycling wouldn't show anything because gas is invisible.
    But if you tie a big feather or orange streamer to the gas nozzle so it flutters, unambiguously demonstrating the danger, then your presentation has 'Punch' .

    old jim
     
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