Why more plumbing sealant might actually cause your leaks
In short: When fixing a leaky pipe, the instinct is to use as much tape and sealant as possible. However, professional standards suggest that overdoing it is a mistake. Learning the precise mechanics of IPS and compression joints can save you from damaging your threads or failing a professional plumbing exam.
Plumbing connections, or joints, rely on specific mechanical interactions rather than sheer force. One common type is the Iron Pipe Size (IPS) joint, which connects pipes of similar or different materials, such as brass or steel. In an IPS setup, such as a brass nipple used in water distribution, the threads are tapered. This design allows the threads to gradually bury into the fitting as they are tightened. Because of this taper, you only need to leave about four threads exposed; over-tightening with excessive strength can damage the threads or the fitting itself.
To seal these tapered threads, professionals use a combination of Teflon tape and pipe dope (thread sealant). A common mistake among homeowners is 'mummifying' the threads in excessive tape. The effective method involves removing the dusty first few inches of the non-sticky tape and wrapping it around the pipe exactly three times in a clockwise direction. When applying pipe dope, less is more: applying it only to the first three threads is sufficient. In fact, during the Master Plumber's exam with the City of New York, using too much sealant is grounds for failure.
A different mechanism is found in compression joints, such as a three-eighths compression coupling. Unlike the tapered IPS joint, this relies on a nut-and-ferrule system. After sliding a nut and a brass ring, known as a ferrule, onto the pipe, the nut is tightened onto the coupling. This action crushes the ferrule against the pipe wall, creating a mechanical seal so tight that the two pieces effectively become one. Because this process permanently deforms the ferrule, any future repair requires cutting the pipe to install a new joint.
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- Summary by Intellect · source: How to Fix Common Leaks | Basic Plumbing
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