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Old 04-30-2019, 05:21 PM   #1
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Mystery Plumbing Fitting

Trying to fix some creative plumbing on my freshwater system. There is some copper pipe connected with a compression fitting to a male threaded fitting. I want to replace that with a hose barb. The male threaded fitting is close to 1/2 NPT but slightly smaller.

I figured it was British (since everything else on my boat seems to be), so I bought a 1/2 BSPT Female x 1/2 NPT Male adapter. That seemed to fit pretty well, although the threads were slightly loose. I attached it and turned the pressure on and it leaks.

So now I am stumped. What fitting is the same size as BSPT but with different threads? Or maybe the same threads but just slightly larger? Or maybe I just put 5 or 6 layers of Teflon tape and call it a day?
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Old 04-30-2019, 05:30 PM   #2
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Picture may help.

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Old 04-30-2019, 08:54 PM   #3
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If is is BSPP it needs a seal ring / washer to seal.

are the threads tapered or parallel. If parallel the fittings need something to seal it like a cone or flat washer.

See
https://www.ralstoninst.com/news/sto...and-bspt-seals
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Old 05-06-2019, 12:35 PM   #4
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Quote:
Originally Posted by Bacchus View Post
This link says that for BSTP fittings "thread sealant is needed to seal the male and female fitting together."

I tried that and it fixed it.
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Old 05-06-2019, 01:37 PM   #5
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I happened to be looking at a Defender catalog today and they had a similar write up re various pipe threads.
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Old 05-06-2019, 04:15 PM   #6
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If it's a tapered thread of any type, it will need a thread sealant.
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Old 05-06-2019, 04:28 PM   #7
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Quote:
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If it's a tapered thread of any type, it will need a thread sealant.
I use 2-3 layers of PTFE tape for all my NPT connections. That does not work for this fitting. I did notice on the UK youtube videos for how to use PTFE tape, they use 10 layers of tape. In the US videos I have seen they only use 2-3. So maybe more tape would have fixed the problem.

Either way, I switched from PTFE tape to thread sealant (dope) and that solved the problem, at least for now. More layers of PTFE might have solved it too.
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