What is the recommended procedure for making threaded PVC connections?

Harvel Plastic, Inc. recommends the use of a quality Teflon ® (TFE) tape having a thickness of .0025” or greater that meets or exceeds military specification Mil-T-27730A for making-up threaded connections. Not more than 3 to 3 ½ mil thickness is recommended. CAUTION: Some oil base pipe joint compounds or Teflon pastes contain ingredients that attack PVC or CPVC piping products. Assurances should be obtained from the manufacturer of the thread sealant that long-term tests with either material (PVC or CPVC) show no harmful effects. A special examination should be made for environmental stress cracking. The suitability of thread paste compounds for use with plastic must be established before use.

Assembly:

Starting with the first full thread and continuing over the entire thread length, ensuring all threads are covered, wrap Teflon ® tape in the direction of the threads. The tape should be started in a clockwise direction at the first or second full thread with a half-width overlap over the effective thread length. It should be wrapped with enough tension, so threads show through the single wrap area. Pipe sizes 2” and larger will benefit from not more than a second wrap due to the greater depth of thread.

Care must be used to avoid over-tightening during assembly. Generally, 1 to 2 turns beyond finger-tight are required to obtain a leak-tight seal for most pipe sizes. Harvel recommends using a strap wrench when making threaded connections, as pipe wrenches, pliers, and similar tools can cause damage to plastic pipes and fittings. Factory testing has indicated that 10-25 ft-lbs. of torque is typically adequate to obtain a leak-free seal. Sharp blows, dropping, or straining of any kind should be avoided. The thread should not be forced. The larger sizes will usually not make up as much by hand and require more wrench makeup.

Note: Harvel Plastic, Inc. does not recommend the use of PVC for threaded connections at temperatures above 100°F (150°F CPVC). Use specialty reinforcement female adapters, flanges, socket unions, or grooved couplings where disassembly may be necessary on PVC or CPVC systems operating at elevated temperatures.

Note: Use of threaded pipe requires a 50% reduction in pressure rating stated for plain-end line @ 73°F

Harvel does not recommend the use of PVC for threaded connections at temperatures above 110°F

Harvel does not recommend the use of CPVC for threaded connections at temperatures above 150°F

Use flanged joints, socket unions, grooved couplings, or specialty reinforced female adapters where disassembly at elevated temperature is necessary

Plastic to Metal Threaded Joints

The American Standard Taper pipe thread was designed for metal pipe with appreciably higher tensile strengths than plastic. Occasionally it may be necessary to make metal to the plastic threaded joint. A male plastic thread can be inserted into a female metal thread if heat is not involved and both lines are anchored immediately adjacent to the joint. Male metal threads should not be connected to a female plastic pipe thread unless specialty reinforcement plastic female adapters are used.