![]() Most materials can tolerate compression loads much greater than tensile. In metallic joints the process of packing increases the stress in the male and female parts yet is tolerated by the strength of the materials. Teflon tape joints serve well in most metallic connections, yet increases the potential for failures in PVC joints.ĭuring the process of tightening a joint the tape is sheared along the flanks, while lubricating, and gets packed into the voids between the root and crest of each thread. Teflon tape can be classified as a "trapped elastomer.” Like imprecise tapered pipe threads it creates an additional variance in the process of joint sealing however, tape is often banned in irrigation systems because of shredding and contamination. Then, when the threaded joint is backed off, such as for alignment, the tape which has been permanently compressed, has lost its packing ability. Second, the additional thickness of the tape adds to the wedging force of the male threads. First, although it is not a sealant, it has been adopted for thread sealing because of its anti-friction lubricity which allows more turns to be taken on a tapered fitting. This creates two additional problems, rather than solving anything. One "solution" has been to wrap the male threads in Teflon tape as a means of packing the joint to avoid leakage. ![]() The purpose of a thread sealant is to “plug” the leak passage. This leak path needs to be sealed during the joint assembly to obtain a drip free connection. All tapered pipe threads have a small spiral leak path between the root and crest of the mating threads. Note the voids left where the crest and root do not meet. This illustration shows how the threaded two parts mate when tightened. Designers and installers strive to reduce the number of threaded joints in a system yet, they are essential for change of materials and convenience of repair. Threaded pipe joints are a necessary evil. With metal fittings these products are acceptable, but when working with PVC fittings the potential for failures is exaggerated. There is a common misconception that Teflon sealant or tape is the best for ALL threaded joints. This is a common question that is asked by installers when assembling PVC tapered pipe threads in a piping system.
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