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Hot Rods Electric fuel pump pipe fitting confusion.

Discussion in 'The Hokey Ass Message Board' started by Pa G., May 24, 2019.

  1. Pa G.
    Joined: Sep 1, 2012
    Posts: 52

    Pa G.
    Member
    from CT

    As I've posted before,I'm re plumbing my fuel system. The electric pump has 1/4-18 NPSF inlets and outlets. I'm running 3/8 fuel line. I have 1/4 male NPT TO 3/8 hose barb fittings for the pump. Is it ok to use 1/4 NPT fittings in the 1/4 NPSF ports of the fuel pump? I assume some type of sealer is needed and plan on using either Permatex aviation form a gasket or the fuel compatible teflon tape. Preferences on sealer? Does this all sound like a decent plan? The big question is that of the pipe thread compatability. Thanks much for any help.
     
  2. lake_harley
    Joined: Jun 4, 2017
    Posts: 533

    lake_harley
    Member

    Glad I didn't post my original thoughts. A quick search yielded this result......

    Both NPT and NPS have the same thread angle, shape, and pitch (threads per inch). However, NPT threads are tapered and NPS threads are straight (parallel). Both threads have a 60° included angle and have flat peaks and valleys. ... While NPT and NPS threads will engage, they do not seal properly with each other.

    BTW, the bold in the quote is from the search, not me.

    Lynn
     
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  3. gimpyshotrods
    Joined: May 20, 2009
    Posts: 15,942

    gimpyshotrods
    Member

    Absolutely not.

    You MUST use 1/4" NPS fittings on the pump.

    If you attempt to put NPT fittings in those ports, you will likely break the pump housing, before you get them to seal.

    The easiest way to get away from a 1/4" straight pipe thread is a GM transmission cooler line fitting. Those are 1/4" NPS male, and will fit the ports on the pump.

    The trick is getting a pair that will go to 3/8" hose.
     
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  4. Pa G.
    Joined: Sep 1, 2012
    Posts: 52

    Pa G.
    Member
    from CT

    Thank you both. I've been driving myself crazy researching this. Lynn,I saw the search results you quoted and found others saying the two would mate and seal with sealer. Lots of confusing contradictory stuff out there. Gimpy,as always you are a great source of info. Again,thank you both.
     
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  5. gimpyshotrods
    Joined: May 20, 2009
    Posts: 15,942

    gimpyshotrods
    Member

    2x: https://www.amazon.com/AN6-6AN-Female-Straight-Adapter-Black/dp/B07CBTS23Z
    One 2-pack: https://www.amazon.com/Russell-6405...omotive&sprefix=1/4+nps,automotive,193&sr=1-1
     
  6. Casual 6
    Joined: May 25, 2008
    Posts: 215

    Casual 6
    Member
    from Great NW

    Just curious as to who makes the electric pump that has the 1/4-18 NPSF tapped ports?
     
  7. Pa G.
    Joined: Sep 1, 2012
    Posts: 52

    Pa G.
    Member
    from CT

    Thank you Mr. G. You never fail to amaze me. Casual 6, It's a Walbro pump. These ports are something of a p.i.t.a.
     
  8. gimpyshotrods
    Joined: May 20, 2009
    Posts: 15,942

    gimpyshotrods
    Member

    Yankee ingenuity.

    I too am from Connecticut.
     

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