NPT Connections: Why Am I Cursed?

[tgordon]

The only time I have seem tapered pipe threads not lead without sealant is when they are a swivel taper seal. I thought if you were using the tape it was no more than 2 wraps of tape. Any more and you risk putting to much pressure on the fitting along with it being more likely to leak. I am no proffesional plumber, but have assembled several fittings on chemical sprayers, hydralic lines, air lines, and water in household. Other than putting to much on your pipes, I have no other ideas for you without being there and seeing what is going on.

 

[bighammer]

I used dope on my fittings for my train horn setup. Compresor was kicking on almost every morning when I'd start the truck. I found a few plugs and fittings that had some of the dope ooozed out. I guess I need to pull it all apart and use tape? (Comp comes at 110 and off at 145)

 

[GHarman]

Ryan, How are your NPT threads coming along? Any leaks? GregH

 

[rbattelle]

Ryan, How are your NPT threads coming along? Any leaks? GregH

I got the latest batch to stop leaking. I always do get them to stop leaking, but only after making and re-making the connections 3-8 times.



Ryan

 

[DJW]

Ryan, I belive the trouble you are having is because you are Deforming the parts, it's easy to do, if the threads are sound, whatever you use as a Lubricant should be sufficient to produce a leak free joint. Often too much pressure at the start, also incorrect use of the tools can cause deformation, therefore leaking joints. Keep the wrench over the threads of the female threaded part, that's essential, if it's in the shape of a nut, use the proper wrench, and Never use the common type used on nuts and bolts. It is very frustrating unable to to make a leak free joint, especially on the first try, but belive me it is possible.

 

[rbattelle]

Ryan, I belive the trouble you are having is because you are Deforming the parts, it's easy to do, if the threads are sound, whatever you use as a Lubricant should be sufficient to produce a leak free joint. Often too much pressure at the start, also incorrect use of the tools can cause deformation, therefore leaking joints. Keep the wrench over the threads of the female threaded part, that's essential, if it's in the shape of a nut, use the proper wrench, and Never use the common type used on nuts and bolts. It is very frustrating unable to to make a leak free joint, especially on the first try, but belive me it is possible.

The way I do it is to thread the fitting in by hand as far as I can, then use an open-ended wrench to go tighter. I've tried using as little as 1 turn past hand tight, and as much as roughly 2. 5 turns.



Is 1/4 turn or 1/2 turn past hand tight more reasonable?



Ryan

 

[GHarman]

The way I do it is to thread the fitting in by hand as far as I can, then use an open-ended wrench to go tighter. I've tried using as little as 1 turn past hand tight, and as much as roughly 2. 5 turns.



Is 1/4 turn or 1/2 turn past hand tight more reasonable?



Ryan

Ryan, 6 Threads min, + if they are loose. GregH

 

[DJW]

Ryan, for instance, if you are threading say a gauge on to a pipe coupling, and the gauge has a Male thread, you can use an open-ended wrench, even though force is transmitted by only two surfaces, if however the gauge has Female threads you Must use a wrench designed for that purpose, otherwise you have a good (should that be Bad?) chance of deforming the fitting and a sure leak. Before tightening a threaded coupling on a pipe, screw a pipe plug in the open end of the coupling to avoid deforming it and thus causing future problems. As regards how tight, in general all tools are designed (except extra long or short) to put sufficient torque for an average person to use efficiently. For pipe, tighten with reasonable force, overtightening can cause leaks by stretching the threads.

 

[rbattelle]

It's amazing, I continue to be cursed by NPT fittings. (AN fittings work fine for me - rarely ever have one leak).

Last summer I was plumbing a gear box in a machine tool with some brass NPT fittings/nipples/valves in various configurations. Box has no pump and operates at ambient pressure, so the only pressure at the fittings is merely hydrostatic (gravity).

All but one or two connections leaked. I was using Block only (no Teflon tape).

I wonder if I'm using too much sealant? Dl5treez commented that too much is as bad as not enough. I tend to load up the threads with the stuff, so that when I screw them together quite a bit oozes out and has to be wiped off.

It's strange - on the first run through of a plumbing job I do all the joints exactly the same. Typically a couple of them will be totally leak free, while the others all leak like crazy.

Ryan

 

[PRout]

Permatex #2. Game over.

 

[rbattelle]

Permatex #2. Game over.

Tried it. Didn't work for me.



Ryan

 

[PToombs]

Ryan, be thankful you're not a plumber. The reworks would kill ya!

 

[TORQUE THIS]

Maybe you need to show a little ***** crack (plumbers crack) while working with pipe... :-laf

When I use teflon tape, I only wrap the threads 2 times.

Are you wrapping the pipe with the tape in the right direction?

 

[rbattelle]

Are you wrapping the pipe with the tape in the right direction?

Yeah, that's not it. I always wrap so that the action of threading the fitting together tends to tighten the tape.



Ryan

 

[TORQUE THIS]

I can't solder copper pipe without leaks if it makes ya feel any better.

 

[rbattelle]

I can't solder copper pipe without leaks if it makes ya feel any better.

Actually, that makes me feel a little better. I'm batting 1000 when it comes to soldering copper pipe. Of course, I pump them full of a TON of solder!



Ryan

 

[DJW]

Ryan, are the fittings you are using off the shelf, or are you cutting some of the threads your self? I know it's very frustrating if one thinks they are doing the right thing and still having leaks (cussing doesn't help either!) generally if threads are being deformed that's the cause of leaks, or are you using electrical threads (parallel) instead of tapered, it's the taper that seals. Talk to a plumber or plumbing shop, they can give you tips. I had a helper that could deform 2" sch. 80 pipe couplings (that's heavy stuff) until I showed him how to handle pipe and fittings. Good Luck.

 

[ScottLauer]

Another thing to consider too is that pipe fittings from different companies might have slightly different tapers. I know they are all supposed to be standardized(I don't remeber the angle) But different operators using different machines might make them slightly different. I don't think thats the whole of the problem but its something to think about when mixing fittings from different companies.

At work we usually use Teflon tape and try to get things as tight as possible. But I work on a Gas pipeline and we deal with over 1000lbs of pressure. We use a lot of swagelocks(mostly tubing though) and they are pretty good fittings. I'm not too familiar with working with lower strength pipe though as all the stuff we work with is SCH 80 or higher.