Purpose of Teflon Tape

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Old 07-31-01, 11:48 AM
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A general question: what is the purpose of teflon tape when attaching threaded plumbing pieces? When is the tape required, and not required? What properties does the tap have: Will the tape swell to seal leaks?

Thanks for the help.
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Old 07-31-01, 02:37 PM
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Teflon tape is used to seal between almost all threaded plumbing fittings, whether it be copper, brass, plastic or steel pipe thread.
About the only exception that I can think of would be brass to brass fittings, and even then, sometimes it is necessary to use teflon tape or pipe dope to seal it.
Teflon tape doesn't swell or shrink.
It usually takes 2-3 flat wraps CLOCKWISE ONLY (or it will unravel, tear up and NOT seal) on male "pipe" threads to form a good tight seal.
Once fittings are tightened down together with teflon tape between them, the tape has to be replaced if the fittings are unscrewed.
I like to use it rather than pipe dope because it is not as messy and won't dry out.
And that's just about all that I know about teflon tape.
Old 07-31-01, 05:12 PM
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Hello mchrist

OldGuy is absolutely correct pertaining to what teflon tape does and how to correctly apply it, etc.

The reason for it's use is to fill any gaps between the threads and reduce friction during tightening. By reducing the friction between the threads, teflon tape or pipe thread compound, allows the pipe fittings to be tightened easier and further together. Which makes a better seal and allows easier removal later on, if need be.

Pipe threads are cut with dies. The dies are not matched and wear differently from useage. Therefore, irregularities are caused on the threads. This causes friction and gaps between the threads. Which in turn can cause leaks.

Simple test is to tighten two identical sets of fittings. One with pipe thread compound or grease and the other without anything applied. The force needed is noticeable between the two sets.

Also the distance up the threads each part travels during the tightening process and the ease it takes is also noticeable. Pipe fittings with tape or compound applied fit together better, hold better and are less likely to leak.

I personally do not recommed the useage of tape on pipe fittings in my forums do to the proceedure needed to apply it correctly and the amount to use. I suggest applying oil or common antomotive grease to the threads.

NEVER use pipe tape on brass fittings or gas appliance connectors. If a connection on a flex connector leaks after installation, find out why and fix it, don't tape it!

And there you have it..."My Two Cents"...

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Old 07-31-01, 06:30 PM
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Thanks for making it clear (I failed to) about not using teflon tape on GAS fittings.
I was referring to water plumbing only, of course.
Old 04-01-13, 09:40 AM
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This is an old thread, but it popped up in my search results. It contains some misleading answers, so I felt obliged to provide the correct answer.

To the OP: you are on the right path when you ask about sealing properties of Teflon tape. The answer is: NO. Teflon tape is not supposed to seal anything. Teflon tape has one and only one purpose: to serve as a lubricant in threaded joints. Lubricant is the key word here. It is a lube, not some sort of gap-filling compound. And this is actually the reason why Teflon tape is only used when joining metal threads. Metal, metal and only metal. Teflon tape is NEVER used with PVC pipes.

You see, the idea of watertight threaded joint is that in order to work correctly (i.e. to be watertight) it has to be tightened securely, which requires certain level of torque. Moreover, if the thread is made properly and tightened properly, it becomes watertight without any additional sealants: no tape, no putty, no anything.

However, one unpleasant property of typical plumbing metals (copper, steel, brass) is that as you tighten the thread, the friction in the threads raises very rapidly to very significant levels. This makes it very difficult to tighten the pipes properly. At certain point the friction (and the amount of torque required to overcome it) becomes extremely high and virtually unachievable in tight quarters. The thread "seizes" before becoming truly watertight. This leads to under-tightened joints and leaks.

This is where Teflon tape comes into play. It acts as a lubricant, preventing the threads from "seizing" prematurely. In presence of Teflon lubricant, metal threads can be tightened to proper torque much easier.

That's the purpose of Teflon tape. That's the only purpose of Teflon tape. Note again, it is not intended to "fill the gaps between threads" as some uneducated people believe. It is just a lubricant.

Now, PVC threads don't suffer from this friction-related problem. The torque requirements for PVC threads are relatively low and PVC threads don't develop any significant friction before the proper level of torque is achieved. Note that the general rule for tightening PVC joints is: finger tighten and then do one or two more turns. This is easily achievable with normal compact tools, with easily manageable leverage and requires no lubricants. This is why Teflon tape is never used with PVC. (And, actually, this is why using Teflon tape with PVC is universally recognized as a schoolbook example of plumber's unprofessionalism.) In fact, applying Teflon tape to a PVC thread can only help to over-tighten it and thus strip the thread and/or split the pipe.

Now, as I said above, properly designed thread joint should become watertight without any additional sealing compounds, if tightened to proper torque. That applies equally to metal pipes and to PVC pipes. However, if you want to opt on the side of caution (just in case you make a mistake), it might be a good idea to use a thread-sealing compound to ensure watertightness. Such compounds are called "pipe thread sealants". You can use such compounds with PVC and metal threads. Just don't try using Teflon tape for this purpose.
Old 04-01-13, 10:04 AM
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Thanks for the additional reply Korben.

Yes on the plumbing test to get your license here in NJ the question is asked, " is Teflon tape or past a sealant or a lubricant?" If you answer sealant you will have got the answer wrong.

Since this thread is so old I will close it..... Please start a new thread with any related issues.
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