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Old 12-24-2010, 10:30 PM   #16
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Leak at dielectric/insulated union


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Originally Posted by Work4living View Post
Look, the misconception is that everyone thinks tape or dope seals threads. They don't.
Their function is a lubricant, they reduce friction to allow the threads to be tightened together and also aide in the loosening. My experience has been tapers in threads male & female do not always match. I usually about 95% of the time use teflon based soft set pipe dope, it isn't cheap. Blue Magic, Select Unyte, Rectorseal, & Gimme the Green Stuff are brands I like. When the dope won't work then I use thin layer of dope then tape and dope again. This practice has never failed me in 29 years.
I agree that teflon tape and dope reduce friction to allow better tightening and loosening of fittings. But, I also think they serve a sealing purpose as they fill any voids where there is no thread to thread contact. After all, we're not using tape/dope on NPT threads which do have some sealing function even without tape/dope.

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Old 12-24-2010, 11:28 PM   #17
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Leak at dielectric/insulated union


I'm lost. We are talking about plumbing, dielectric unions sealing the joint of the union and nipple. They are npt threads.
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Old 05-19-2011, 07:41 PM   #18
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Leak at dielectric/insulated union


The origin of a lot of confusion about "thread sealing" has to do with the twofold nature of the sealing.

1. Tapered NPT threads must form a leak-tight seal against each other.
2. The threads must be sealed against corrosion (because ultimately a corroded thread cannot maintain a leak-tight seal). This is especially important in transitions, e.g. from iron to copper, even in an ostensibly "closed" system, because variations in pH level (resulting from frequent fresh-water fills because of leaks or overpressure situations) can make the closed system resemble an open system.

A sealing-cord such as Loctite 55, for example, will help to create a leak-tight seal from day one but will do nothing to seal the threads against corrosion over time.

So you have to be clear when phrasing the questions:

Will this product help the thread to make a leak tight seal against the opposite thread?

Will this product seal the thread against corrosion?

Will this product and that product used in tandem do both?

Can such-and-such product used alone do both?

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