Fittings Not Fitting

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by Knight, Dec 4, 2019.

  1. Knight

    Knight New Member

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    I have a Shako valve that supposedly has 1/4" NPT ports (purchased from overseas... I'm in the US). I went to Home Depot and purchased a 1/4" nylon barb to go in one end of the valve and a 1/4" NPT brass hex nipple to go in the other end. The nylon barb will not even start going into the port and the hex nipple (which is tapered) goes in only about two threads and then stops. I have re-checked the size specifications of the barb and hex nipple, which both clearly state 1/4".

    Is this normal for these fittings to be so tight and do I just have to wrench them in with more force? I don't want to damage the valve. Any suggestions? Thank You.

    upload_2019-12-4_17-47-9.png
     
  2. Tuttles Revenge

    Tuttles Revenge In the Trades

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    Go back to your hardware store and see if they have a thread guage. Its probably metric threads.

    Google produces a USA and a UK result too.. british threads!
     
    Last edited: Dec 4, 2019
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  4. Reach4

    Reach4 Well-Known Member

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    Maybe you did cross-thread the nylon piece.

    You could also compare the threads on the two pieces you bought. Are they the same pitch?

    The thread gauge is the right tool to check the block, but I kinda thought the photo made the threads on the nylon piece look to be finer pitch that the brass piece.
     
    Last edited: Dec 4, 2019
  5. Terry

    Terry Administrator Staff Member

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    I'm thinking they are metric too. They should thread in more than that.
     
  6. Knight

    Knight New Member

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    Thank you for your input. I had that thought as well (that one or the other was metric) I'm going back to the store tomorrow.
     
  7. Reach4

    Reach4 Well-Known Member

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    Take your Shako valve with you.
     
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  8. Knight

    Knight New Member

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    I never went past that point in the picture with the nylon barb. I do have one barb that fits well/easily into the valve. I do not know the specs on this barb. The valve is supposedly 1/4" NPT, however the hex nipple, which is also supposedly 1/4" NPT does not fit. Here is a picture of the threads and their corresponding fit into the valve.

    upload_2019-12-4_21-57-3.png
     
  9. Knight

    Knight New Member

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    Thank you for your response... confirming my thought that they should screw in farther than they are. Something is really 'off' here and I can't quite figure it out yet.
     
  10. Reach4

    Reach4 Well-Known Member

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    https://en.wikipedia.org/wiki/National_pipe_thread says to expectabout 4 turns for Hand-tight engagement.

    Dies and taps can fix up threads that are too tight. I suspect out of spec NPT rather than metric, but it certainly could be a metric problem.
     
  11. Knight

    Knight New Member

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    Just want to thank everyone again for their input. On a hunch, I ordered some 1/4" BSP barbs from ebay and they finally came in (from China so delivery to US took many weeks). They screw right in effortlessly, all the way to the 'nut' portion of the barb, just like the unknown one I pictured. So clearly this valve I have is not NPT, but rather BSP. If nothing else, I sure learned a lot from this situation. Happy New Year to you all.
     
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  12. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    Well, maybe, maybe not! https://www.ralstoninst.com/news/story/the-difference-between-npt-bspp-and-bspt-seals
    It could be bspp, which requires a gasket rather than pipe thread to make the seal.

    A bsp fitting and socket would get tighter as you tighten it, as the pair are tapered, similar to NPT, but with a different thread pitch and angle of taper. A bspp fitting would screw in without tightening, but need a gasket, similar to a hose's washer, to make the seal.
     
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  13. Knight

    Knight New Member

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    Just when I thought I had it figured out! Thanks for the link. You must be right because these easily screw all the way in by finger and actually have an ever-so-slight, and I do mean slight, 'wiggle' to them as I screw them in. So they probably would need a gasket and/or some teflon tape to make them water-tight. They won't be under pressure.
     
  14. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    Tapered pipe fittings seal by jamming the sealant in to that tightening gap sort of like a wedge. A straight thread will not create that tapered tight fit. Those require the gasket, and the head of the fitting compresses it to the body of the fitting, making the seal. Tape or pipe dope probably won't solve the issue on a straight fitting, or if it does, would only do it at a low pressure, otherwise, you'll just have the fluid or gas just leak around the threads.
     
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  15. Tuttles Revenge

    Tuttles Revenge In the Trades

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    The seal may be at the shoulder of the male fitting where it contacts the female.. or it may be a gasket at the base of the female fitting where the tip of the male fitting would bottom out.
     
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