Holley 12-879 pressure regulator

Discussion in 'Fuel and Air Systems' started by 7dart0, May 31, 2018.

  1. 7dart0

    7dart0 Well-Known Member

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    I just bought this regulator from summit racing. It said 3/8 npt for fitting size. Well the inlet and outlet are much bigger and the return port is smaller. What gives.

    Anyone use this style regulator that can help me with fitting size?

    Thanks Tom
     
  2. SMCARNUT

    SMCARNUT Well-Known Member

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    I have used them and the ports are 3/8 national pipe thread maybe yours was boxed wrong? If my memory is correct they offer in NPT or AN style fittings.
     
  3. SMCARNUT

    SMCARNUT Well-Known Member

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    Here is a size chart so you can measure threads.

    NPT%20chart[1].jpg
     
  4. 7dart0

    7dart0 Well-Known Member

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    The big holes measure 17.20mm, the smaller return home measures 13.13mm.
     
  5. SMCARNUT

    SMCARNUT Well-Known Member

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    Sounds like it was either machine wrong or boxed wrong I have used two of these and had no problem with the sizes. I would call Summit racing and let them know they have very good customer service.
     
  6. 7dart0

    7dart0 Well-Known Member

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    I went to Lowe's and the 1/2 flare fitting screwed in perfect. And I had a 6an fitting laying around and that screwed in to the return port
     
  7. pishta

    pishta I know I'm right....

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    The below table gives the Threads Per Inch, Pithc and Major Diameter for NPT Threads.

    Trade Size Threads per inch Pitch Major Diameter (O.D)
    Inch mm Inch mm
    1/8 27 0.03704 0.94082 0.405 10.29
    1/4 18 0.05556 1.41122 0.54 13.72
    3/8 18 0.05556 1.41122 0.675 17.15mm (major diameter OD)

    Pipe is always measures in ID and tube is OD, so a 1/8 NPT fitting is huge compared to a 1/8 tube.
     
  8. 7dart0

    7dart0 Well-Known Member

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    So for some reason mine is drilled and tapped for 10an in and out, and 6 an for return. I'm going to exchange it and see if the new one is the same.
     
  9. Ironmike

    Ironmike Well-Known Member

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  10. Ironmike

    Ironmike Well-Known Member

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    I have a 12 841. Think they're all 3, 1/2 NPT. I have dash 8 in, out, and return.
    20180604_135614.jpg
     
  11. 7dart0

    7dart0 Well-Known Member

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    Update**

    Just got the replacement regulator with some part number stamped on it with different but correct 3/8 npt tapped fittings.

    The original one was obviously stamped with wrong part number. I'm just glad summit made good on it.

    Tom