MEET THE PLASTICS

• Plastic (more correctly thermoplastic) for plumbing comes two ways: in pipe sizes and in tubing sizes. While both are sized nominally according to inside diameter, pipes go by iron-pipe sizes and tubes go by copper-tube sizes. Pipes and tubes and their fittings, even in the same designated sizes, should not be interchanged. With plastic piping, you choose from a wide selection of materials. Table A shows the plastic plumbing materials available and describes what each is used for.
  
  
• Rapid technological advances in plastic plumbing may leave local plumbing codes outdated. So, before purchasing your materials, it's a good idea to consult your city or county building officials.
  
  
• DWV stands for the drain-waste-vent system used to carry wastes away from your home's fixtures and to vent the system above the roof. Sewer pipes are made to carry household wastes below ground to a public sewer or private disposal system. Drainage pipes are used below ground, too, but are thinner-walled and lower in cost. They're usually used with non-septic water, such as roof runoff. Tubular goods are the thin-walled fixture drain and trap parts used beneath sinks and washbasins.
  
  
• Only two kinds of plastic tubes can withstand hot water under pressure: rigid CPVC and flexible PB. The two may be used singly or together to build corrosion-free, non-electrolytic household water supply systems. Because plastic pipe is non-conducting, it cannot be used for electrical grounding.
  
  
• PVC pressure pipe should be used only for cold water outdoors. It is ideal for building lawn-watering and irrigation systems. PE pipe serves a similar purpose but is flexible and cannot be solvent welded. PE is especially useful as deep-well pipe.
  
  
• Riser tubes are the highly flexible, small-diameter tubes linking a water supply system and faucets, making the faucets easier to connect. Riser tubes often fit directly into an adapter on a fixture shutoff valve.
  
  
• Plastic pipes for most uses (except tubular products) are rated by the American Society for Testing and Materials (ASTM). Look for the ASTM designation on each pipe, tube and fitting that you buy, signifying that it meets ASTM standards. Water supply piping should carry the National Sanitation Foundation's "NSF-pw" approval, meaning the parts are suited for carrying potable, or drinkable, water.

SOLVENT WELDING

• The simple solvent-welding process used to join many plastic pipes must be done properly to prevent leaks.
  Here's how.
  
  
• Use the two-step method–employing cleaner/primer and solvent–except with ABS and styrene, with which the one-step method (solvent only) is usually enough.

  1. Inspect the pipe end and fitting socket for cracks, gouges, dirt and abrasion. If the pipe end is imperfect, it can be cut back to expose good material. Discard a damaged fitting.

  2. It's a good idea to purchase pipe and fittings made by the same manufacturer. If this isn't the case, test-fit them. The pipe should enter the fitting but meet resistance part-way in. Held upside down, the pipe should not fall off.

  3. Cutting pipes. Cut the pipe off squarely to the proper length using a fine-tooth saw or plastic pipe cutter (a hacksaw works well). Flexible plastic pipes are more easily severed with a sharp knife, but be careful not to cut yourself. If you have a large amount of cutting to do, you can get a tubing cutter with a special wheel for use on rigid plastics or a shear-type cutter for PVC. Then, using a knife, remove any burrs and chamfer the outer end of the pipe slightly (Fig. 1). Do not use sandpaper on plastic pipes. It may remove too much material for successful joining.

  4. Cleaning. Now, using a quality cleaner/primer, clean the pipe end and fitting socket (omit this entire step with ABS and styrene). Apply the cleaner/primer with a dauber, brush or clean cloth to remove grease, oil and dirt, and to prepare the plastic mating surfaces for solvent cement action. The surfaces to be joined should be clean and free of dirt and grease. The pipe should be dry before applying cement.

  5. Solvent welding. Brush on a coat of an ASTM-rated solvent cement that is matched to the type of pipe and fitting you are using. It is important to use the right type of solvent cement. Table B shows the various cements and the kinds of plastic they are suited to. Liberally apply cement first to the pipe end (Fig. 2), then apply it sparingly to the fitting socket (Fig. 3). Leave no bare spots. With chemical-resistant PVC and CPVC pressurized piping, give the pipe two applications of cement–one before and one after coating the fitting socket. With all solvent welding, use a dauber or brush that's at least one-third to one-half the pipe's diameter to apply the cement.

  6. Immediately join the pipe and fitting full-depth with a slight twist to bring it into correct alignment. The twist breaks up insertion lines in the solvent cement. Hold the fitting on until the solvent cement grabs tightly. A fillet of cement around the fitting indicates that you used enough solvent cement to ensure a leak-free joint. With PVC and CPVC, do not wipe off the fillet. On the other hand, the one-step solvent-welding method for ABS and styrene calls for wiping off any excess cement around the fitting. The joint should be ready for use in an hour.

• Safety precaution. Avoid prolonged breathing of solvent cement and cleaner/primer vapors. Work in a well-ventilated area, and cap the cans after each use. Keep solvent and cleaner away from any open flame. Read and follow the precautions that appear on the labels. Remove any cement on your hands with hand cleaner.
  
  
• Correcting errors. Solvent welding is normally a one-way process–you can install the fitting, but you cannot get it off again. When you accidentally put the wrong fitting on a pipe, you must cut it out and replace it with the correct fitting (Fig. 4).

FIG. 7 - Plastic water tubes can be joined to metal using flare or compression adapters. To use a flare adapter, the tube end must first be flared with a flaring tool.