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  1. #1
    Join Date
    Jun 2013
    Location
    Yakima, WA
    Posts
    98

    High Elevation Gas Orifice Deregulation

    Can anybody point me to a chart for resizing gas orifices (nat & lp) in high altitude? I have a Blodgett DFG100-3-S stacked convection oven going to live at a resort in Montana at 7,500 feet elevation. I have converted it to LP with an OEM conversion kit, and emailed the factory as to orifice size. A tech emailed back saying they need to be #43 orifices. I questioned it and he said it was a typo, s/b 53. I couldn't understand why the orifice would be enlarged with higher altitude. Now I'm back to the original size for LP and not trusting what I'm being told. I would like to find a chart to confirm. Thanks.

  2. #2
    Join Date
    Jan 2014
    Location
    New England
    Posts
    514
    To me your better off following the manufacture spec. on altitude than a generic chart as it may affect warranty if there are issues with this equiptment further down the line. Doesn't this manufacture have a live person to talk to ( A Technical Rep. ) granted you may have to pay for the call. Possible if you email them again you may get a different rep. If they say #53 also then that is what you should use, if they say something different ,then you can question why your getting two different orifice numbers.

  3. #3
    Join Date
    Oct 2008
    Posts
    784
    Here's Blodgett's technical supplement for GENERAL TECHNICAL INFORMATION FOR COMMERCIAL APPLIANCES. You'll find their table for "Equivalent Orifice Sizes at High Altitudes" in it:

    http://manuals.therrconline.com/rrcm...supplement.pdf


    As Bazooka Joey suggested, you should still call Blodgett to confirm what you find in this manual. It's THEIR publication, so let them know this.


    "You never know what others don't know." -

    If I can't laugh at myself...then I'll laugh at YOU! -

  4. #4
    Join Date
    Oct 2004
    Location
    Central WA
    Posts
    1,532
    OK, somebody chime in with the combustion theory here - were going to higher elevation, so thinner air, and richer burn, right? So mfgr says (per his tech support email, and ECTO's chart) put in a BIGGER hole...

    Please somebody 'splain.

  5. #5
    Join Date
    Oct 2008
    Posts
    784
    CJ, I don't have my bit set with me right now, but I think the orifice diameter is smaller as the number goes higher, just like "wire" Gage sizing. It' s a gage size.

    Sent from my HTC0P3P7 using Tapatalk


    "You never know what others don't know." -

    If I can't laugh at myself...then I'll laugh at YOU! -

  6. #6
    Join Date
    Oct 2004
    Location
    Central WA
    Posts
    1,532
    Quote Originally Posted by ECtofix View Post
    CJ, I don't have my bit set with me right now, but I think the orifice diameter is smaller as the number goes higher, just like "wire" Gage sizing. It' s a gage size.

    Sent from my HTC0P3P7 using Tapatalk
    Looks like you're right. I've never paid attention, and i've never drilled out a spud - i just assumed thousandths like an ac piston.

    Thanks!

  7. #7
    Join Date
    Oct 2008
    Posts
    784
    Well smeq, my work hours had kept me from really looking at what you're concerned with.

    The DFG-100 is specified for #40 orifices for NG and #53 for LP for a around 27.5k of BTUs of output from each of the two burners. The oven is rated @ 55k BTUs total output.

    You're running LP @ 7500 ft. The supplement I'd posted earlier says to go to a #54 from 2000 to 7000 ft and #55 @ 8000 ft. Not a huge difference, but I know you want the ovens running at optimum efficiency.

    I'm curious. Will Blodgett send you the new size orifices? Or...did they say it's okay like it is with your conversion kit? Just wondering...

    I'm asking because when they came to town for our training years ago, they were the ones who were most adamant and thorough about getting down to the basics such as this and other stuff I learned in my first few years doing commercial appliances (before CFESA training became so prevalent). Being an in-house tech now, I don't have a need to call them much anymore.
    Last edited by ECtofix; 05-08-2014 at 10:32 AM.


    "You never know what others don't know." -

    If I can't laugh at myself...then I'll laugh at YOU! -

  8. #8
    Join Date
    Jun 2013
    Location
    Yakima, WA
    Posts
    98
    Thanks so much for the excellent input and response. My factory guy started with the wrong orifice size due to not dividing the total btu's by the number of burners. We've all been there. You are correct, Ecto, and I just found out that I will be going to this Montana resort at 7500 feet to start up my equipment. I will bring blanks as backup but do not anticipate gaining very much going from 53 to 54. At least I have the chance to adjust the air now. Also found out that the customer is still adding other equipment to his order and this could end up being a great project.

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