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Very small water drip at threaded valve body connection. Is Teflon tape better to use

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honda1998civic

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Very small water drip at shower valve threaded connection. Can Teflon tape withstand heat? All the connections are copper and sweated up to the threaded connection to shower valve body. It held for as long as a week with leak test but yesterday a drip started. I don't see how because I tightened the connections until I basically have one or two threads showing. I used Teflon paste thinking that was better than the tape. I know I need to try and get another round on connection now but it's all sweated together so I have to cut line or heat up solder to disconnect. I'd like to disconnect as close to the valve body as possible but will Teflon tape withstand heat when I sweat lines back together? Also are the threaded connections tapered? I did back off maybe quarter of a round on one of the threaded connections because it was not lining up. I had already sweated the elbow to threaded connection along with six inches of line so I could solder away from the valve body. Any suggestions are appreciated. Is Teflon tape versus Teflon paste a preference or better in certain situations?
 
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RossABQ

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honda1998civic said:
... I used Teflon paste thinking that was better than the tape. I know I need to try and get another round on connection now but it's all sweated together so I have to cut line or heat up solder to disconnect. ... Also are the threaded connections tapered? I did back off maybe quarter of a round on one of the threaded connections because it was not lining up. ...
Click to expand...

I'd assume this is an NPT (pipe thread) connection, so Yes, it's tapered. You for sure can't back off a quarter turn.
 
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robertlynk

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I would check to see if you cracked the valve. One of the big problems I've seen with using a lube type of sealer is that people tighten them to tight and split the castings. Used to see it all the time on the fuel pumps for Detroit diesels. Now I use loctite thread sealer if possible
 
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rlitman

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robertlynk said:
Used to see it all the time on the fuel pumps for Detroit diesels. Now I use loctite thread sealer if possible
Click to expand...

That's fine on a fuel pump, but not fine for plumbing.

Teflon tape will take the heat of sweating, though it can soften and loosen a little (but not as much as dope). The pink tape (or blue, or any "high density" version) will handle heat much better than the white stuff.

The right way to do this is to solder the threaded fittings onto stubs of pipe, screw the stubs into the valve body, and then sweat the stubs onto couplings.
 
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honda1998civic

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Ok. Thanks for the advice folks. Guess I'll tear it back down and add a coupling in there. All the sweating held fine and the one time I decide to use Teflon paste it backfires in me. I was under impression the paste was better than the tape but from now on its tape on everything I do. I never liked the paste because its too messy but my pops swears by it so I tried to use it. But this was the last straw. I really don't think I cracked anything because I was pretty careful but ya never know. I'll let you guys know what I find out. Thanks for all the quick replies. So far this is probably the best place to come to when needing help and not wanting to spend that green paper on a so called professional..
 
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jhelrey

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I use tape and paste. The paste is more for lube to thread on. Just don't over tighten or you could crack the brass.
 
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Scott r c

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rlitman said:
That's fine on a fuel pump, but not fine for plumbing.

Teflon tape will take the heat of sweating, though it can soften and loosen a little (but not as much as dope). The pink tape (or blue, or any "high density" version) will handle heat much better than the white stuff.

The right way to do this is to solder the threaded fittings onto stubs of pipe, screw the stubs into the valve body, and then sweat the stubs onto couplings.
Click to expand...

What he said. You can also throw a damp rag on the valve body to keep the joints cool while you solder the couplings.
 
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honda1998civic

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Jhelrey. I'll definitely inspect the valve threads when I take it apart. I really hope It isn't a crack. I don't think it is but you never know. Just trying to make a leak proof connection for life!! :) Last thing I expected to leak was the threaded connections. But guess I'll get it right the second time.
 
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honda1998civic

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Ok. Day 1 after taking fittings apart and everything looking good. The threaded connection seemed little loose when I was taking it apart so assuming the problem was all I needed was to snug up a little more but took all the threaded connections apart and used Teflon tape.


So no cracks, none of that other bad stuff.. Just needed a little more *** behind it
 
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Gerald O

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Teflon tape, paste, pipe dope, these things are all primarily for lubrication of the threads while tightening pipe joints. Tapered pipe-thread is designed to be self sealing. If it does not seal based on the threaded joint itself, then anything applied to the threads as a 'sealer' is not really reliable.

You can't judge whether a pipe joint is sufficiently tightened by the number of threads showing. The threaded length in pipe threading is usually not that well controlled. This can effect whether the tapers can seat tightly enough to seal. It's not that unusual to have a defectively threaded joint that is never going to seal reliably. More often it will be the ****** that is over or under threaded
 
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PoorOwner

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The blue teflon tape at lowes is very good for this
But sometimes with plumbing you thought you got it tight but due to the space or short tool / lack of grip a lot of times it was not tight enough
 
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rlitman

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Gerald O said:
Teflon tape, paste, pipe dope, these things are all primarily for lubrication of the threads while tightening pipe joints. Tapered pipe-thread is designed to be self sealing. If it does not seal based on the threaded joint itself, then anything applied to the threads as a 'sealer' is not really reliable.
Click to expand...

Groan, not this again...

NPT tapers have a helical leak path. They MUST have a sealant applied to the threads or they WILL leak.

NPTF tapers (which cannot be made steel to steel, because the thread pattern requires deformation of the mated threads) have no such leak path, and will seal tight against fuel (what they were designed for) without any sealants required. These are not commonly used in plumbing fittings though.
 
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Gerald O

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rlitman said:
Groan, not this again...

NPT tapers have a helical leak path. They MUST have a sealant applied to the threads or they WILL leak.

NPTF tapers (which cannot be made steel to steel, because the thread pattern requires deformation of the mated threads) have no such leak path, and will seal tight against fuel (what they were designed for) without any sealants required. These are not commonly used in plumbing fittings though.
Click to expand...

You are correct that the thread geometry itself is not self sealing. It is the deformation that occurs at the end of the taper where the threads are incompletely formed and somewhat at the ridges in that area. That's what the lubricant is for, prevention of galling at the high pressure points of contact where the slight deformation is occurring.

I worked many years pipefitting in industrial plants using all metal types, stainless, etc, carrying all kinds of nasty chemicals, and high pressure. I'd have been fired if I couldn't make leak free joints without relying only on 'thread sealant'.

https://www.colder.com/Portals/0/Li...ture/WhitePapers/Documents/NPT_whitepaper.pdf
"Despite the standards created to maintain uniform
fittings, tapered pipe threads are inexact and
during the course of use and repair the threads can
become damaged and susceptible to leakage. The
area where the crest and the root of the thread
meet can form a spiral leak path no amount of
tightening will eliminate.
A pressure tight joint is achieved by the compression
in the threads resulting from tightening. This
compression and sealing occurs in the first few turns
of the internal thread. As wrenching takes place,
material from both the male and female threads
deform into each other. This ensures full thread
contact which minimizes spiral leakages.
Click to expand...
 
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rlitman

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From your own quote:

The area where the crest and the root of the thread
meet can form a spiral leak path no amount of
tightening will eliminate... full thread
contact which minimizes spiral leakages

NPT will NOT seal without a sealant. Period.

In the case of the OP's shower valve, the amount of pressure required to sufficiently deform the thread area to "minimize" spiral (sic) leakage would surely crack the valve body. In addition, NPT threaded connections are designed to be reusable. Once the threads have deformed, they will no longer seal properly when removed and re-used.
 
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honda1998civic

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Loving the debate. But it was a very small small drip that could have easily been stopped with a half turn at most. My problem was I had soldered everything up to threaded connection making it a little more frustrating. But believe problem solved. Atleast I hope it is if not ill go with the stretched threads and go buy a new valve body. Anyway. More than enough info from the post. Really appreciate it...
 
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Gerald O

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rlitman said:
From your own quote:

The area where the crest and the root of the thread
meet can form a spiral leak path no amount of
tightening will eliminate... full thread
contact which minimizes spiral leakages
Click to expand...
That part of the quote is referring to the uniformly threaded area. The next paragraph refers to the seal that is achieved at the ends of the threaded area which deviate from the uniform taper.
NPT will NOT seal without a sealant. Period.
Click to expand...
Rubbish.
Detroit ****** Works said:
http://www.detroitnippleworks.com/n-p-t-national-pipe-thread-*******/
N.P.T. ******* consist of a tapered threading which has “imperfect threads” at the end of the threading. The “imperfect threads” create your seal when connecting a male to a female N.P.T part. The seal is created by torquing the NPT threads. When the National Pipe Thread fittings are torqued, the threads flanks compress against each other creating a successful seal....

The metal to metal connection of a male to female NPT fitting or ****** will deform after the required torque, which completes your seal. It is important to note that disassembling and then reassembling the same threaded fittings is not recommended. This is because after you set a NPT fitting connection, you have formed the threads to that specific connection, trying to reconnect those already formed NPT fittings or ******* with another NPT fitting or pipe will create leaks because your seal will not be properly formed.
Click to expand...
In the case of the OP's shower valve, the amount of pressure required to sufficiently deform the thread area to "minimize" spiral (sic) leakage would surely crack the valve body.
Click to expand...
Not true unless it is made with a different material significantly weaker than the pipe fitting. So that means brass (or bronze or copper) to brass, iron to iron, plastic to plastic, etc. He's probably got a brass or bronze shower valve body, and a copper or brass fitting.
In addition, NPT threaded connections are designed to be reusable. Once the threads have deformed, they will no longer seal properly when removed and re-used.
Click to expand...
NPT is not intended for repeated assembly and disassembly for that very reason. New fittings should be used only once in critical applications.
 
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Gerald O

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honda1998civic said:
Loving the debate. But it was a very small small drip that could have easily been stopped with a half turn at most. My problem was I had soldered everything up to threaded connection making it a little more frustrating. But believe problem solved. Atleast I hope it is if not ill go with the stretched threads and go buy a new valve body. Anyway. More than enough info from the post. Really appreciate it...
Click to expand...
Good on you for getting it to seal. Backing it off 1/4 turn definitely didn't help the situation. Never back off.
 
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honda1998civic

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Roger that gerold. I honestly didn't think a quarter turn would have mattered with me snugging it up so good. But made sure I didn't back off any this time. :thumbup:
 
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