Mystery Plumbing Fitting

[Rain Dog]

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?

 

[Lou_tribal]

Picture may help.

L

 

[Bacchus]

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/story/the-difference-between-npt-bspp-and-bspt-seals

 

[Rain Dog]

See
https://www.ralstoninst.com/news/story/the-difference-between-npt-bspp-and-bspt-seals

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.

 

[Bacchus]

[emoji106]
I happened to be looking at a Defender catalog today and they had a similar write up re various pipe threads.

 

[AusCan]

If it's a tapered thread of any type, it will need a thread sealant.

 

[Rain Dog]

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.