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

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On Sun, 12 May 2013 19:01:18 -0500, Vic Smith wrote:

Here are the exposed threads on what I ended up with on the schedule 40 fitting:

And here are the exposed threads on the schedule 80 nipple (this is the one that I had the Teflon tape + sealant) after I removed the Teflon tape and sealant due to what I read in this thread - and started over:

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I think we all understood that's what he meant.
 I have no experience at all with threaded plastic pipe.

I agree. For that matter, Teflon tape is widely used and if it made a huge difference, there would be leaking fittings everywhere. Yet, lots of people, including many pros are using tape.

Imagine pushing a v shaped wedge into a v cut opening in a piece of plastic or metal. The further in the wedge goes, the more splitting force you have. Do you think with the same amount of force applied to the wedge, it will go in further with or without lube?

Agree. That's where experience counts. And why perhaps those with little experience could wind up in trouble using Teflon tape while others have used it and it's worked fine.

And there I disagree. Joints are tight when they are tight. If you try to rely on looking at how many threads are showing, I think you're in for trouble. How do you even know that the number of threads is consistent from one pipe to another? For example, if you get a piece of pipe cut and threaded at HD, is piece A going to have exactly the same number of threads as piece B? You just have to develop a feel for it and learn from experience.

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On Mon, 13 May 2013 06:09:12 -0700, snipped-for-privacy@optonline.net wrote:

I should also note that the original fittings certainly had Teflon tape on them, presumably from the professional installers.
I did have leaks in the two inlets to the pool pumps though; but who knows why (hopefully they're fixed with the new fittings).
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a

" professional installers" ??? yeah, right! from the layout, they look like hacks
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e a

+++++1
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Depends on when it was built but with that hidden cover storage & automatic cover.... 200k ain't far off.
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wrote:

d

<>>>>>>> And there I disagree.   Joints are tight when they are tight.

Actually, two things work in our favor.... threading machines have automatic stops & molded parts are consistent (and hopefully the tooling was "proofed").
Of course there is always some variability of the parts & how much tape (that's dope is better for plastic) but the number of turns to "make up" after finger / hand tight is pretty consistent.
Pipe threads have a standardized / designed thread form.....well, unless they come from China :)
Seriously pipe threads are very consistent unless made by a total hack shop...which is happening less & less as 3rd world mfrs learn (ie get parts rejected)
IIRC pipe threads might even have torque limits for "tight joints"...too lazy to look it up.
cheers Bob
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On Sat, 11 May 2013 08:22:29 -0500, Vic Smith wrote:

Interesting conclusions.
I noticed a LOT of my threaded fittings are gray (schedule 80?) and most of the glued "end" fittings (near the pumps & valves) are gray thicker stuff (schedule 200?).
Asking at a pool store, they said they use gray fittings near the pump "because they handle heat better".
Yet, that article says both teflon tape and schedule 80 fittings are a no no.
Interesting though the schedule 40 PVC tensile strength of 7K psi and the PVC thread "resistance" of 400K PSI.
For 2" pipe, apparently each turn past finger tight adds 0.00239 inches per inch, times that 400K psi, nets almost a thousand psi per turn (956 psi per turn).
The chart gives us only about 4,000 PSI as the maximum allowable (3912 psi); so it seems that 4 turns past finger tight is the maximum one can go with schedule 40 PVC.
In summary, that article recommends, for my 2" PVC plumbing: 1. Pipe dope (not teflon tape). 2. Two turns after finger tight (never more than 4). 3. Only schedule 40 plastic (no schedule 80).
It was also interesting that a single threaded fitting reduces the strength of the system by half the original strength!
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I saw no place that says "no chedule 80". It says DO NOT MIX 40 and 80 schedule.
Harry K
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..

+1 Good point...
I agree, it didn't say "no sch 80" ..... it said going to sch 80 & expecting that to avoid a splitting problem was wrong.
Sch 80 will give you higher system pressure & better resistance to misc mechanical loads but it won't solve the tape or over tightening problem. :(
cheers Bob
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s...

I learned _my_ lessong on changing from iron to PVC in the middle of January with a foot of snow on the ground. I had used a male iron-to- pvc female. That was out in the middle of a pasture and ovf course there were no shutoffs on the line anywhere. Future runs I made all _started_ with a shutoff and 'male irong-female PVC fittings were banned. :)
Harry K
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wrote:

So with Sched 40 pipe, no Sched 80 fittings.right??
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On 5/11/2013 7:49 PM, snipped-for-privacy@snyder.on.ca wrote:

...

...
Well, that's not QUITE what it says...it says Sch 80 isn't be needed on Sch 40 properly installed...Sch 80 is overkill but can't really hurt anything.

Can't hurt unless again they're severely over-torqued...
What it's really trying to say is that Sch 40 fittings _properly_installed_ are all that a Sch 40 system needs to meet the pressure requirements that Sch 40 is rated to hold. (Which, of course, only makes sense else't a component would be underdesigned in comparison with the rest of the same components.)
What they're driving at is as the other responder said above is that the correct solution to splitting Sch 40 fittings isn't to go to Sch 60 or Sch 80 and get by w/ over-tightening them but to install Sch 40 correctly instead.
--


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ter/TheDosandDontsThreadedPlas....
Bingo!
Vic has posted an article that would have been my next comment....
The use of tape can lead to splitting of the female threaded fitting.
Loctite makes a product specifically aimed at plastic threads..
No-More-Leaks
As T4 points out, the article notes that threaded joints reduce pressure capacity by 50% (due to wall thickness reduction). A side note...in steel piping threading also greatly reduces corrosion life and that's why we see corrosion evidnence and leaks at the threaded joints. :(
Specifically, the article's comments about sch 40 vs 80 were related to the behavior of threaded fittings.
SInce the threaded behavior & subsequent resulting stress is driven by the wedging action.... a thicker fitting will be just as stressed (to the first order approximation) as the thinner sch 40 fitting. Both are "wedged" open to the same extent when tightened the same number of turns .
The articles's comment was to emphasize that a thicker fitting is not the answer.... proper sealant (not tape) is the answer.
cheers Bob
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wrote:

I've never done plastic plumbing except some glued PVC long ago, but have dealt some with plastic threaded fittings. Besides the stress on the female, the threads themselves are much more easily deformed than galvanized. IOW, strippable. It's too easy to wrap too much tape on plastic, so my first thought was to just use a dope that can squeeze out, and relieve stress, Didn't know about "sealers," but if I worked with plastic I'd find out what to use for the particular plastic. Trickier than galvanized really, which I've done a lot of. There's always some danger listening to "old-timer" advice if they aren't current on "technology." I'm a long-time fisherman - like my dad's entire family - and it wasn't until I started reading fishing magazines that I found out about the improved clinch knot and started using it. Told my dad it had something like double the strength of the simple double overhand knot he used and I had used. He ignored me of course. Then one time we were fishing in Ontario, and he hooked a big Northern. Line broke when we almost had it landed. I showed him the curl at the end of his line where it had broke at the knot. He used the improved clinch after that. Now I understand there's something better than the improved clinch knot. Six-turn San Diego jam. I'll have to check that out. Sounds interesting.
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On Sat, 11 May 2013 11:44:48 -0700, Oren wrote:

I'm actually surprised that I apparently put too much on, according to your comments.
I thought that's how much you're supposed to use.
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On Sat, 11 May 2013 12:34:33 -0700, Oren wrote:

I called RectorSeal while I was at Home Depot and they said to use the red tube that I bought (and not the red jar, which was for metals).
The red tube says it's for "plastics", so that's what I used over the Teflon tape.
Now I understand, from Vic Smith's article, that Teflon tape is a no-no; and I understand that *lubrication* is a no no ... so it appears *all* the tubes of sealant I bought from Home Depot are wrong.

I wonder if the local plumbing and irrigation supply places know this stuff?
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Danny D:
No, the way I read that Lasco article, you should not be using EITHER pipe dope OR teflon tape on plastic pipe threads.
You should be using a thread sealant meant for plastic threads ONLY. The Lasco article really should come out and say that pipe dope is not the same thing as thread sealant meant for plastic threads. It dances around that point by saying that pipe dope hardens whereas thread sealant for plastic pipe threads doesn't, thereby allowing it to be pushed into leakage paths by the water pressure inside the pipe, thereby blocking that leakage path. It also says that pipe dope and teflon make the threads slippery, thereby reducing friction and causing overtightening, whereas a thread sealant meant for plastic threads won't do that.
Putting the thread sealant on the male threads, then wrapping them with teflon tape is just as bad as using teflon tape only. The thickness of the teflon tape you put on is going to increase the spreading force on the female fitting making it more likely to split.
From my reading of that Lasco article, you should apply thread sealant meant for plastic threads to your male plastic threads only, and then screw on the female plastic thread. Tighten to finger tight and then no more than two full turns after that.
If you've already used teflon tape on your threaded plastic joints, and there's no splitting or leaking, I would just leave them as is. But, in future, just use the red bottle that says it's meant for plastic and nothing else.
I think everyone in here understands the principle of tapered threads, and that the idea behind teflon tape or pipe dope is that these materials get compressed between the make and female threads to seal the joint against leakage. That Lasco article said that metal threads can gall at metal-to-metal contact points, and that the use of teflon tape or pipe dope helps to prevent that. In the case of a smooth plastic-to-plastic thread contact, there's no risk of galling so you don't need anything as thick as pipe dope or teflon tape to keep the metals separated until the joint is fully tightened. With plastic theads, all that's needed to seal the tightened joint is a fluid that's viscous enough not to be pushed out of the joint by the water pressure inside the pipe. I'm thinking that plastic fittings can be molded to much better tolerances than iron pipe can be machined (because the cutting tool wears down for one thing), so a fluid that's fairly thin may still be viscous enough to not be pushed out of a small enough crevice in a threaded joint. Or, at least, at the lower water pressures that plastic piping is suitable for. So, even if this thread sealant you bought for plastic piping seems to be too thin compared to pipe dope, I would still use it by itself, which is what Lasko is telling you to do.
--
nestork


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On Sun, 12 May 2013 08:41:40 +0200, nestork wrote:

Actually, I put the Teflon tape on first ... and then put the gooey stuff on. Now I know that both of those solutions was dead wrong!
In fact, it's extremely hard, it seems, to find the "right stuff" at the home box stores that meets the three requirements: a) PVC b) Non lubricating c) Sealant
Here is a large-format photo of the tubes of wrong "stuff" I bought:

* Harvey's TFE Paste, Part No. 023015 * Front: White slow setting superior quality pipe thread compound * Rear: Non-hardening, withstands up to 3,000 psi (gases) at temperatures from -50F to +400F and 10,000 psi (liquids) from -50F to +400F. Use on water, steam, natural, & LP gas, oils, fuels, & dilute acids. Apply to clean male pipe threads on metals, PVC, CPVC, ABS, polypropylene, and nylon. Lubricates as it seals; will not harm seals of valves or faucets.
* Rectorseal Tplus2 Pipe Thread Sealant, Product Code No. 23710 * Front: Seals and lubricates threaded connections on metal & plastics. Formulated for potable water, natural gas and a wide variety of fluids and gases. Teeny tiny print: Meets CSA requirements working temperature range -40F to 125F. Maximum working pressure 125 psi. For use with natural gas and LP (vapor state only). Use on steel, galvanized steel, iron, brass, copper, & aluminum. For pipe size up to & including 1 1/4".
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Bingo! +2 T plus 2 is the goop to use.
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