Plumber's tape needed?

[Tom Veatch]

...

Or gain? If a compression fitting leaks, sealant on the threads won't do a thing to help contain the leak.

Tom Veatch Wichita, KS USA

[Upscale]

Thanks Lew. I'll dream tonight of fairy princesses all draped out in yellow Teflon tape. :)

[Jack Stein]

I happen to have a hunk of 3/8 copper tubing with a compression fitting in my junk pile, which you made be go down and look at... couldn't see any notable issues that would preclude it's usage in a high flow situation, other than it was 3/8" in pipe. I guess there might be some negligible constriction which is difficult to see and might be important in super small pipe, but in normal home air systems in this discussion, a very non-issue.

I tend to think that the amount of air that would flow through a 3/8" pipe under 1000 lbs of pressure is more than would flow through the same pipe with 2 lbs of pressure? Is that wrong? I know volume and pressure are two different things, but I'd think one effects the other?

Most easily illustrated by example:

See, right there I don't get it? In my mind, to get high pressure you need to restrict the flow. I don't see a mountain stream or a river as high pressure? I admit I know next to nothing about fluid dynamics, but thats my point... For example, if I have a high pressure hose, and put a hole in the hose, the water will shoot out the hole into the air, and the more pressure, the higher it will go. The mountain stream is not shooting up in the air, just flowing... low pressure, high volume. My mind says the only way to get high pressure in a mountain stream is to force in through a pipe of some sort. I do realize that the deeper the stream, the higher the pressure at the bottom of the stream from the weight of the water.

Well, if you think about it, the main difference is a spring holds the compression fitting together instead of threads. Pipe dope is not needed anymore there than on a standard brass compression fitting.

[Jack Stein]

I said you "could" do it, and "suggested" it would have the same value as doping the threads in a brass compression fitting. I never suggested one should do it. I understand pipe dope might make a threaded steel/iron joint easier to loosen, but not in brass, brass doesn't rust, doesn't need pipe dope to make it easier to disassemble.

[Doug Miller]

Teflon tape isn't worth a toot as a sealant anyway, but it's a dandy lubricant.

[Doug Miller]

One man's negligible is another man's noticeable, I suppose...

No, you're not wrong, and indeed the pressure does affect the flow rate -- but flow rate is also determined by the size of the pipe. You're going to get a higher flow rate through a one-foot diameter pipe at 2psi than you will through a 3/8"-diameter pipe at 1000psi.

That's not correct.

Steeper gradient = higher force (due to gravity).

I should have made it more clear that I meant that as an analogy to try to make the point. I did not mean that the mountain stream is literally under higher pressure.

Except that you won't be unscrewing one of those. Threaded fittings *are* from time to time unscrewed, and doping them on assembly makes disassembly easier.

[Doug Miller]

Of course it doesn't rust -- but it *does* corrode in the presence of weak acids, or salts.

Evidently you've never had the experience of trying to disassemble a corroded joint in brass...

[Tom Veatch]

Or gain? If a compression fitting leaks, "lubricant" on the threads won't do a thing to help contain the leak.

In fact, since a compression fitting can be overtightened, with adverse effects, lubricant on the threads may be contra-indicated. I've never encountered a compression fitting (or a flare fitting, for that matter) where sealed or lubricated threads would be any benefit either in assembly or disassembly.

Here, I assume we are talking about compression fittings

not tapered pipe threads which seal by interference fit (compression) between the male and female threads. Another post in this thread seems to blur the distinction between those two categories.

Tom Veatch Wichita, KS USA

[Tom Watson]

I use teflon tape, double wrapped in a clockwise direction and do not cover the entry thread. Carefully used, the tape will take up the slop in the threads and provide a better seal, while not allowing the metal to metal joint to seize.

I don't have my Machinery's Handbook in front of me but, if you refer to it, you will find that there are a number of interference fit thread engagement tolerances and what we too often get in offshore fittings is a slop tolerance that is really more than it should be.

Pipe dope comes in flavors (caustic, pneumatic, hydraulic, etc) and I think there is more chance for contamination because the wet surface can attract gunk in what is often a dusty environment - and because I'm more capable of keeping the entry thread clean with the tape.

Regards,

Tom Watson

[Doug Miller]

I didn't say that it would.

You've evidently not had the pleasant experience of ever having to open ten-year-old flare fittings on a propane line in a basement with a dirt-and-cinder floor. Humidity + cinders = slightly acid environment = corrosion; I believe that the job would have been a bit easier, had the threads been doped when they were put together. Yes, I realize those aren't the same as compression fittings, but the point is that brass *can* corrode, and if it does, it *can* be much harder to disassemble than one would wish. Doping the threads before assembly avoids that problem.

My assumption also.

[Larry W]

Hey, guys, lets stick to topics we know something about, like electricity.

(paraphrasing a formerly prolific rw poster)

[Luigi Zanasi]

C'mon Larry, the plumbing, 'lectric & politico-religious threads allow those who know nothing about woodworking to pontificate.

L.

[RonB]

Holy Crap!

72 Posts on Plumber's Tape!!!!!!!!!!!!!!!

You guys are life-deficient.

RonB

[Luigi Zanasi]

Good troll for a non-political question. :-)

Luigi

[Upscale]

But, but, but.... I got to dream of women draped out in Teflon tape.

That's a life isn't it?

[Robatoy]

We did pretty well with a 'summer dresses' thread-jack once.........those were the days. Summer dresses are wonderful... unless it's on that bitch Ann Coulter, then anything looks like a pillowcase full of doorknobs.

[Tom Watson]

u be dissin' blANNd cOOter?

dincha never think 'bout bumpin' uglies wif a 10 speed bike?

Regards,

Tom Watson

[jo4hn]

And then there was Robin's butt (Hartl not Lee). The stuff of wet dreams, that. 8-O

[Lew Hodgett]

----------------------------------------------------- We did pretty well with a 'summer dresses' thread-jack once.........those were the days. Summer dresses are wonderful... unless it's on that bitch Ann Coulter, then anything looks like a pillowcase full of doorknobs.

---------------------------------------------------------

Look out, Palin's back.

So youl have another pillowcase full of doorknobs to join Coulter

Lew .

[Robatoy]

Last wet dream I had, I dreamt that there was a hole in the eaves- trough , and that my window was open, and that the wind was blowing rainwater into the bedroom... . . . . I used to like wet dreams.