Question just about the order of pipe dope sealant and teflon tape

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Q: Does the order of the tape & pipe sealant matter?
Starting with this:

Just wondering, if, for critical 2" PVC applications such as pool equipment, when using *both* pipe sealant & teflon tape:

Does it matter if we put the teflon tape first:

And then the pipe sealant?

Before screwing the fitting into the housing:

Just curious: Q: Does the order of the tape & pipe sealant matter?
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Danny D wrote:

I'd use one or the other, not both.
Teflon is primarily a lubricant and is most effective on NPT fittings. NPT fittings change their pitch so that the connected pieces deform the pipe threads more and more making the seal.
Other types of threading do not change the thread pitch (if there is any involved in the seal), so any imperfections are better dealth with by a pipe sealant.
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T

ipe

a plumber friend uses tape and then dope, on every joint to avoid leaks
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wrote:

Does he wear a belt and suspenders too?
I know people that use both, but I know people that use one or the other and don't have leaks. One advantage of tape is when you take it apart five or ten years later, it is probably going to be easier. Joint compound can get hard.
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Actually, I do both. Tape, dope, belt, suspenders. For real. . Christopher A. Young Learn more about Jesus www.lds.org . .

Does he wear a belt and suspenders too?
I know people that use both, but I know people that use one or the other and don't have leaks. One advantage of tape is when you take it apart five or ten years later, it is probably going to be easier. Joint compound can get hard.
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wrote:

When I put pipe dope on my suspenders, they never leak.....
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When I wrap myself in teflon tape, I slide off the chair and under the table. . Christopher A. Young Learn more about Jesus www.lds.org . .
When I put pipe dope on my suspenders, they never leak.....
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I use one or the other too, never both. Usually I use tape. And I rarely have a problem.
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I can get hard too!!!! (even without Viagra)....
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wrote:

Pipe or dope - not both. Read the instructions on either one.
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T

ipe

A lot incorrect information.....
1) Teflon is primarily a lubricant << it is material to seal the naturally occurring / designed in clearance between internal & external pipe threads.
2) NPT fittings change their pitch so that the connected pieces deform the pipe threads more and more making the seal. <<<< incorrect for ubiquitous / normally used / everyday NPT threads. :(
NPT pipe threads do NOT have interference thread forms, they do not change pitch. If they deformed, how could new fittings be used on old pipe?
"Dry fit" pipe threads do exist & do seal based on interference but they are seldom encountered in daily life. I used them ~30 year on military hydraulic systems where dope & tape were prohibited. Dry seal threads are a bitch to use, they sucked... a major PITA. Be thankful that everyday threads are not as you describe.
Take a look at the wikipedia article on pipe threads.
cheers Bob
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DD_BobK wrote:

Likewise, look at the article on thread sealing tape:
"One of the defining characteristics of PTFE (Teflon) is how good it is at defeating friction. The use of PTFE tape in tapered pipe threads performs a lubricating function, which more easily allows the threads to be screwed together, to the point of deformation, which is what creates the seal."
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wrote:

Just because it is a lubricand doesn't mean it is not also a sealer - and vise versa. If all you need is a lubricant, just oil the threads and see how well it seals - or grease the threads. It is a combination product.
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On Sun, 12 May 2013 16:05:09 -0400, clare wrote:

I ended up using the 2-in-one lubricant + sealer, after taking pains to remove all vestiges of the Teflon tape.
BTW, do we lubricate the unions?

I think they go on dry ... but I also thought Teflon tape was to be used on the threaded fittings (and that was wrong).
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You can put some silicone lube on the rubber o-ring. That is what seals it. Nothing goes on the threads.
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t

a

HB-
Please provide sight / link for following.....
""One of the defining characteristics of PTFE (Teflon) is how good it is at defeating friction. The use of PTFE tape in tapered pipe threads performs a lubricating function, which more easily allows the threads to be screwed together, to the point of deformation, which is what creates the seal."

I assume you mean deformation of the threads? & not the tape?
Internal & external threads of NPT threads type do not interfere with each other. Take a look in Machinery's Handbook to get an idea of the design of NPT threads. There is a designed in & manufactured in clearance between the crests & the valleys.. thus creating a spiral leak path that needs a sealant not a lube.
cheers Bob
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m

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d

I should add to be clear....
NPT threads need a sealant to seal the spiral leak path. NPT threads do not seal by thread deformation.
Hint: To do a practical proof of want I knew to be the design intent of NPT threads, I did the lube alone assembly of NPT pipe & fittings.... they leak no matter how tight. :( I used oil so that no "sealant" was present. :)
cheers Bob
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On Mon, 13 May 2013 04:43:10 -0700, DD_BobK wrote:

Are the union threads NPT also?
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'Caryn[_2_ Wrote: > ;3061321']

Caryn:
"NPT" means "National Pipe Thread", and NPT threads are a tapered thread, like this:
[image:
http://www.plumbingsupply.com/images/npt-thread-taper.jpg ]
A waterproof seal is achieved by some soft material (like teflon tape or pipe dope) being compressed between the male and female threads as the joint is tightened.
Other threads, like the threads on a bolt or a light bulb are not tapered:
[image:
http://www.instockfasteners.com/IMAGE/BM_81307000H__21.jpg ]
In plumbing, you can tell which threads to put teflon tape, pipe dope or thread sealer on by just asking yourself the question: "In this connection, is the water tight seal made by the threads themselves?" If so, then you need pipe dope, teflon tape or thread sealer on those threads. If not, then you shouldn't put anything at all on those threads.
So, in the case of the union shown here:
[image:
http://www.hartindustries.com/images/threadedunions150.jpg ]
The two threads where pipes screw in at each END of the union are NPT threads and would need pipe dope, teflon tape or thread sealant on them because it's the threads themselves that make the water proof seal at those joints.
However, the coarser thread on the collar of the union is not a tapered NPT thread and doesn't need pipe dope, teflon tape or thread sealant on it because it doesn't make a water proof seal. The water leakage path through those collar threads is prevented by the O-ring shown inside that union (as seen in the picture). It's that O-ring that prevents water leakage through the collar threads, not the threads on the collar wedging themselves together as the joint is tightened like NPT threads do.
So, with the above union, you would put pipe dope, teflon tape or thread sealant when screwing the union onto the pipes it's meant to connect. But, you wouldn't put anything on the collar threads when connecting the two halves of the union together. The teflon tape, pipe dope or thread sealant would prevent leakage through the pipe threads, and the O-ring prevents leakage though the collar threads.
Hope this helps.
--
nestork


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Missed this...
Are the union threads NPT also?
No, threads on unions are some sort of straight thread. The purpose of the union thread is to provide a means to compress the seal; o-ring, brass insert or union material depending on design of union.
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