Threaded Connections
- Cutting and Deburring
PVC or CPVC pipe should be cut squarely and smooth for easy and accurate threading. A miter box or similar guide should be used when sawing is done by hand. Burrs should be removed from inside and outside using a knife or plastic pipe deburring tool. - Threading Pipe
Threading PVC and CPVC pipe can be accomplished easily using either a standard hand pipe stock or a power operated tool.Cutting dies should be clean and sharp.
Power threading machines should be fitted with dies having a 5°negative front rake and ground especially for thermoplastic pipe. Self-opening die heads, and a slight chamfer to lead the dies could speed up the operation; however, dies should not be driven with heavy pressure or at high speeds.ln case of using a hand held cutter, the pipe should be fixed in a pipe vise.
To prevent crushing or scoring of the pipe by the vice jaws, protective wrap should be applied such as canvas, emery paper, rubber, or light metal sleeve. For hand stocks, the dies should have a negative front rake angle of 5° to 10°. PVC and CPVC material could be threaded easily; caution should be taken to avoid over-thread. - Apply PTFE Tape
After threading, a ring gauge should be used to check the accuracy of the threads.Tolerance should be within ±1-1/2 turns.The threads should then be cleaned.After cleaning, apply a thread lubricant such as PTFE tape to the threads. Wrap the tape around the entire length of threads beginning with the second thread from the end.
The tape should slightly overlap itself while going in the same direction as the threads.This will prevent the tape from unraveling when the fitting is being tightened on the pipe.Overlapping in the wrong direction and the use of too much tape can affect tolerances between threads.This could generate stress on the wall of female fittings and cause failures during operation. - Assembly of Threaded Joints
After applying tape, screw the threaded fitting onto the pipe. Screwed fittings should be started carefully and hand tightened only.Threads must be properly cut and covered with good quality thread PTFE tape. If desired, the joint may be tightened with a strap wrench. Do not use a stillson type wrench.The jaws of this type of wrench will scar and damage the pipe surface.Thread assembly should be tightened until hand tight with an additional 1 to 1-1/2 turns. Avoid stretching or distorting the pipe,fittings or threads from over tightening.
(1) Never apply solvent cement to thread pipe or thread fittings. Do not allow cleaners, primers, or solvent cements to"run"or drip into the threaded portion of the fitting.
(2) Some PTFE pastes contain chemicals that may be harmful to the pipe and fittings.You should consult the supplier or manufacturer of the paste before use.
(3) Avoid screwing metallic male threads into thermoplastic female threads. We recommend flanged end connections for joining a metal system to a plastic system. There are a variety of thermoplastic fittings that are designed with metallic male or NPT female thread inserts.The corrosion resistance of the metal insert will have to be taken into consideration. Consult the factory or your LD sales person for the availability of these metal-insert fittings.
