Pipe thread sealing....

[mrcaptainbob]

In the coarse of updating the plumbing, (I'm using copper), I've run into a situation of having several leaks. All the soldered joints were fine. But nine of the threaded joints leaked. I put about 3 to 4 wraps of teflon tape and snugged the fittings down good, but about half of them leaked. My son said he spoke with a master plumber and it was suggested to use the dope AND the tape! I took the leakers apart and rewrapped with 4 to 5 wraps and then added the teflon dope on the first 1/8". Well, they don't leak now. I clockwise spiral wrapped the threads. Is this the method to use? 5 wraps of teflon AND teflon dope?

[LazyPup]

The treads commonly used on plumbing fittings are tapered threads. The diameter of the theaded section increases from the end of the pipe to the rear part of the thread. In theory the pipe should seal itself without the application of any sealant material, however, due to the coarseness of the thread it is nearly imposssible to tighten a joint enough to effect a good seal without some form of sealer or lubricant.

The teflon tape commonly found in hardware and home supply stores is actually intended to be used only as thread lubricant to assist in tightening the treads.

Although it is difficult to find outside of a plumbing supply house, there is a variety of teflon tape that is 3/4 inch wide and about three times as thick as the tape found in the hardware and home suppply centers. By manufactures specifications, even the heavy guage tape is only certified as a thread sealer when three overlapping layers are applied.

Never put teflon tape on unions or on flare fittings as it will interfere with the prescision machined mating surfaces.

Dope is the preferred method to insure good tight joints.

Teflon joint compound (teflon dope) is a mixture of teflon and pipe dope. The Dope effects the seal, while the teflon works as a thread lubricant to insure good tight mechanical seals.

When selecting Pipe dope you must be careful to select a Dope that is rated for the type of service you are working on, Water, natural gas, propane, high pressure air, hydronic heating lines,steam, fuel oils, gasoline etc.

The preferred dope most often used by plumbers is Non-Hardening Rector Seal. Rector seal has the advantage that is is almost universally rated for all the different services. In addition, a non hardening dope remains resilient which aids in removing fittings later for servicing.

While discussing threaded joints, there are some other points to keep in mind:

The code specifically prohibits using female threaded PVC fittings in water distribution systems (UPC606.2.2 & IRC 2904.16.2) If connecting PVC to copper the proper method is to use either copper x PVC unions or use female copper fittings and male PVC adapters. ( Note,,if using copper by PVC unions it is best to solder the copper end before gluing the PVC end to prevent heat damage to the PVC section)

Because of the galvanic reaction of dissimilar metals Copper may not be connected directly to either galvanized or black iron pipe. To connect copper to iron pipe you must use either approved dielectric unions or you may use a 6 inch bronze nipple as a transition fitting.

Teflon tape should not be used in conjunction with pipe dope.