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  1. #1
    Join Date
    Feb 2013
    Location
    Champaign, IL
    Posts
    44

    Flame running back to orifice

    Bryant M# 312AAV036070ACJA S# 1906A19772

    Had been switched over to LP at installation by a previous company. They did the springs and orifices, but did not install the low gas pressure switch or spoiler screws that are to be installed in the burners. We installed the low gas pressure switch, but held off on the spoiler screws that are supposed to be installed into field drilled holes in the burners - I wasn't clear on the function of these screws and didnt want to be drilling uneseccary holes in th burners or in the wrong places. Any ideas on what the function of these screws is?

    Also, when the furnace is running in second stage, flame will randomly run down inside the burner towards the orifice. This happened on all three burners at different times. Seemed to happen more (but not isolated to) when furnace was powered up with a call for 1st and 2nd stage already in place. What is it called when the flame does this, and any ideas as to what would cause it?

    Inlet GP: 11
    Outlet GP: low 5.85 high 10

  2. #2
    Join Date
    Aug 2004
    Location
    S.E. Pa
    Posts
    6,275
    Flashback- caused by high primary aeration with low manifold pressure, high port loading/ poor burner design. Many burners require additional turbulence to properly mix the air/ fuel. Due to LP requiring 2.5 times more O2 than NG, it is not always possible to get the proper mixing by atmospheric injection from a venturi.

    Sometimes, an LP burner can flashback when it is level or worse, tilted back towards the orifice. Since LP is heavier than NG, it tends to flow downhill. Sometimes this can be cured by a slight downhill pitch away from the venturi. I''d double check on that burner. Are there any ports (holes) than seem blocked or otherwise obstructed? Any crud inside the burners?

    I can't stand mfrs. that want us to drill holes unsupervised into precision controls of theirs such as this. Any agency granting a listing on this basis is not to be trusted. The mfr should engineer their burners properly and if modifications are required for different fuels, they should offer a factory replacement part. I used to do this all the time with fireplace conversions. Many units required an entire burner change for LP.

  3. #3
    Join Date
    Jul 2000
    Location
    Northern Wisconsin
    Posts
    2,035
    You'll find putting the screws in the burners, as required by the LP conversion instructions, will probably resolve the problem.
    Use the biggest hammer you like, pounding a square peg into a round hole does not equal a proper fit.

  4. #4
    Join Date
    Feb 2013
    Location
    Champaign, IL
    Posts
    44
    Thanks for the info guys! I also talked to Bryant tech support and was told that putting the screws in the burners almost always takes care of the issue. I need to make sure we have the right screws and we will be going back to finish the job. Thanks again for the information.

  5. #5
    Join Date
    Aug 2007
    Location
    Northern VA 38 degrees N by 76 degrees W
    Posts
    5,060
    Quote Originally Posted by Gerbs1983 View Post
    Thanks for the info guys! I also talked to Bryant tech support and was told that putting the screws in the burners almost always takes care of the issue. I need to make sure we have the right screws and we will be going back to finish the job. Thanks again for the information.
    The screws ad turbulence and increases mixing of the fuel and primary air

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