Teflon Tape

[DD_BobK]

Hey Bub-

What is the source of the posted quote?

What follows is a cite of a site .... :) that confirms my experience YMMV

The complete details of pipe threads (tapered threads) are somewhat nuanced...

some are meant to be used with sealant (dope or tape) NPT some are meant for "dry fit" NPTF

NPT vs NPTF

THREAD DESIGN The requirements for NPT (National Pipe Thread) are spelled out in ANSI B1.20.1 The requirements for NPTF (National Pipe Thread Fuel) are spelled out in ANSI B1.20.3

those interested in the details can take a look at .......

YEARS ago when I worked on the design & manufacturing of some hydraulically powered hardware (AH-64 AWS Ammunition Feed System) the Army required that no sealant or Teflon tape be used any pipe threads in all "deliverable" hydraulic systems.

We were required to use NPTF (dry seal) threads; all components & fittings. These threads were precisely machined and required precision gauges to assure that they would, in fact, mate and seal. They were a bitch to work with but they did "dry seal".

"Normal" pipe threads lack the precision to develop reliable sealing without the use of tape or dope....hence the use of sealants with pipe threads.

For years (my aerospace years), I used Teflon tape on non-deliverable hardware (shop systems, test rigs, lab equipment, etc)

I switched to dope for residential work based on the suggest (actually, chiding) of a master plumber.

For a while I used both tape & dope....now I'm back to tape alone (the thick Mil-Std stuff) or if I'm feeling nervous about thread quality...then it's BOTH.

Also for PVC to metal threaded connections........PVC into metal NEVER metal into PVC.

cheers Bob

[HeyBub]

See also:

[Tony]

Really? I'd like to know for sure for in the future.

[Tony]

>>>> Psst! It doesn't matter. The tape is not the sealant.

It is referring to threads being screwed together with teflon, not soldered or with pipe dope or anything else.

Yummy! I love WD-40 in my morning oatmeal!

[Tony]

Actually now that I look at it, my also contains teflon.

[Tony]

Funny, mine says "lubricates and seals".

It's a *lubricant*

So why did mine break before making a seal? I tried both teflon and pipe dope. (not both at once)

And now I know what? To use hose clamps on threaded PVC fittings?

[Tony]

"Lubricates and seals all threaded joints."

[Tony]

What brand and product do you use?

[Tony]

It's a dessert topping and a shoe polish!

I'm thinking I heard it on "Dr. Demento" but it sounds like a SNL skit.

[Tony]

That's it! Not sure where I got the shoe polish from. Was it in the same skit?

[Bob F]

PVC is just not tough enough to resist the forces of screwing a metal male fitting into ta PVC female fitting. The female expands and breaks before a seal if formed in many cases. The hose clamp solution can increase the success rate. PVC rated pipe dope works better than teflon, in my experience.

[Bob F]

They make special fittings for this. Brass female on one end, PVC slip joint on the other.

[Bob F]

I've had bad luck with 1 1/2" - 2" PVC joints. Does the dope/string work well for those?

[Tony]

>>>>>>> Psst! It doesn't matter. The tape is not the sealant.

Thanks. Next time I will know better! I was actually redoing it the same way it was done the first time (because it had a slow leak) I guess I now know why it leaked the first time!

[Existential Angst]

>>>>

It should -- it's virtually foolproof, albeit a messy pita. Sewing thread works well, also, if the string is too thick/bulky. And there are all thicknesses of sewing thread, as well.

It seems that, from other posts in this thread, that the closest one gets to a seal between pipe and fitting, the better the joint. Which suggests as thin sewing thread + dope that will do the job..

One way to gauge this might be to screw a joint together with dope by itself, see the net "penetration", and then choose a thread weight that gives you 90-95% of this penetration. Thick string could cut this penetration in half, which means a lot of string is between the mating parts, which could, over time, dry out and poss. leak -- in theory.

Teflon dope is proly a good idea w/ string/thread.

[Existential Angst]

>>>>>

Oh yeah, with steel male and female PVC, thread/dope is proly pretty good stopgap, as a seal will occur before the PVC fitting distorts/cracks.

[Bob F]

This is definately worth trying. I assume I'd wrap thread up the PVC pipe threads, then smear dope over it to hold it in place for installation, cut off the inside end of the thread and screw the pipe together. Is that right?

[Existential Angst]

Actually, it's easier to dope up the threads first, and wrap the thread into the dope -- holds the thread nice. Then, screw together, snap off/snip off any excess string. Much less juggling this way.

Heh, iffin yer feeling creative, you might could try a very lightweight fishing line.... the Q would be, is the nylon fishing line more compressible than the PVC material.... If this works, the fishing line would never dry out.... if that is even an issue with doped-up thread.

[Bob F]

I would imagine the dope would get soaked into the thread and keep it from degrading. Hmmmm. I wonder how waxed dental floss would work?

[Existential Angst]

Perfect!!! The cheap generic stuff is nice and thin, the brand stuff thicker. But you won't be snapping any of this stuff -- bring yer scissors!!