Sealing leaky NPT fittings

[Dayzedandkonfuzed]

NPT fittings, by design, seal on the threads and do not require any kind of sealant. At least that's what the weatherhead rep told me. As consumers of these fittings, we know that's a load, because everyone makes their sh*t to a different standard.

I use liquid thread sealant, that way if the fittings are actually well made, it will just push all the sealant out; and if they're not, it should seal.

 

[mc1984ss]

NPT fittings, by design, seal on the threads and do not require any kind of sealant. At least that's what the wearherhead rep told me. As consumers of these fittings, we know that's a load, because everyone makes their sh*t to a different standard.

I use liquid thread sealant, that way if the fittings are actually well made, it will just push all the sealant out; and if they're not, it should seal.

This is correct, the taper is what is supposed to seal them. I have even seen in some racing applications where a npt fitting is installed into a straight pipe thread hole. This is not something I like but it is done. This summer I had a 1/4" npt fitting leaking past the threads. No matter how much I sealed it or tightened it it would leak. I pulled it apart to find out the threads had bottomed out and was not able to tighten properly therefore not sealing. Alot of times what also happens if a fitting is used multiple times it will slightly wear. At this point if it is reinstalled it will have to go in further than before.

 

[L92 OLDS]

It’s possible to over tap an NPT thread. If you go to deep it will not seal. The same holds true of the threads are worn. If the threads are in good shape and tapped correctly you shouldn’t need sealant. Sealant doesn’t hurt though and can be used if your threads are messed up

 

[64nailhead]

It’s possible to over tap an NPT thread. If you go to deep it will not seal. The same holds true of the threads are worn. If the threads are in good shape and tapped correctly you shouldn’t need sealant. Sealant doesn’t hurt though and can be used if your threads are messed up

X2^2

'Threads are in good shape' - OP's carb base plate from probably a 30+ year old card that had a steel fitting in it for eons. When that fitting was removed, the threads were no longer in good shape I'll bet.

No matter of the exact cause - 592 sealant / liquid teflon won't hurt and will stop any possible leak. Much easier just to put it on and forget about it.

 

[abbey castro]

Remove the fitting from the carb base as well as the hard line that attaches to it. Lightly sand paper the end of the hard fitting to remove burrs. Put thread tape on it and reinstall. Pull back the fitting on the hard line and lightly sandpaper the hard line by rotating the line. Reinstall with no sealant on this fitting. As for the barb fitting the threads are probably messed up. Put thread tape on it.

 

[Clone TIE Pilot]

Thinking about applying some penetrating loctite on the fittings. That way I won't have to disturb the parts more.

 

[jiho]

These discussions always amaze me. I've always used Teflon tape on inverted flare fittings, wrapped around the threads on the nut and folded over the flare on the tube -- including the fittings on fuel pumps. None of the tape has ever dissolved, and I've never had any leaks. Without tape I've always had leaks. Of course you have to wrap it the right direction.

 

[fleming442]

I thought the Teflon was for lubricating the threads to get them tighter, not seal them...

 

[lilbowtie]

Something isn't right - it's not like your trying to seal any kind of pressure-vacuum. Check for splits cracks.

 

[Clone TIE Pilot]

I

Something isn't right - it's not like your trying to seal any kind of pressure-vacuum. Check for splits cracks.

I am trying to seal vacuum. Both fittings are causing nasty vacuum leaks that are leaning out my fuel mixture.