• Meet the Plastics
• Solvent Welding
• Mechanical Couplings
• Installing Plastic Piping

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 Rapid technological advances in plastic plumbing may leave local plumbing codes outdated.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.

FIG. 1 - To join the solvent welding plastic pipe to its fittings, first cut the pipe and then deburr it with a knife. FIG. 2 - Solvent weld the joint with a cleaner/primer followed by a liberal application of solvent cement to the pipe's end. FIG. 3 - Next apply solvent cement sparingly to the fitting socket. If the joint is to be pressurized, give the pipe a second application of cement.   FIG. 4 - If you solvent weld a fitting incorrectly, you can saw it out and install the correct fitting. Use two couplings to join the new parts to the old.

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. 5 - PE pipe cannot be solvent welded. Instead, it uses barbed fittings and stainless steel worm-drive clamps.   FIG. 6 - PB tubing is joined to its fittings with mechanical couplings shown here in the form of tees. 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. FIG. 8 - Plastic tubular drains and traps are joined with slip couplings that allow length and angle adjustments before tightening the slip jam nuts. FIG. 9 - Pressurized joints between metal piping and plastic hot/cold water supply tubing, such as at a shower valve, should be made with transition unions.

MECHANICAL COUPLINGS Some fittings are made for joining pipes and tubes that cannot be solvent welded. PE pipe. Simple barb-type plastic or metal fittings are used with flexible PE pipe. To make the connection, slide a correctly sized worm-drive clamp over the pipe end and push the pipe all the way onto the barbed fitting (Fig. 5). Position the clamp about 1/4" from the end of the pipe and tighten it. With any flexible tube, be careful not to bend it in too tight a curve. It can kink the tube and diminish or completely shut off the water flow. PB tubing. Flexible polybutylene tubing for hot and cold water supply systems is joined by patented O-ring-sealed mechanical couplings. Each system uses its own coupling, and they're often not interchangeable with those of other systems. Follow the instructions for the kind you are using (Fig. 6). Flaring plastic. Both CPVC and PB tubing can be joined to each other or to metal piping with the use of flare or compression couplings and adapters (Fig. 7). Flaring is done with a flaring tool. To prevent cracking of a CPVC tube when flared, cut the end off squarely and smoothly with a pipe or tubing cutter. Soak the rigid tube's end in boiling water just before flaring. Slip-jam-nut couplings. Tubular drainage pipes are joined by slip-jam-nut couplings. To make up such a coupling, first install the nut facing its threads. Then install the correct-sized slip washer with its flat face toward the nut. If you are sure that none of the parts are made of ABS plastic, which is adversely affected, you may use plumber's putty or silicone rubber sealant around the inside of the slip jam nut to prevent leaks. Adjust the length and direction of the tubular parts, then start the nut's threads with its fitting and tighten (Fig. 8). Most plastic tubular couplings will tighten leak-free by hand, but you may want to give them an extra quarter-turn with a pair of channel-locking pliers. Transition unions. For adapting plastic water supply tubing to threaded metal parts, such as at water heaters and bathtub/shower valves, use a fitting called a transition (Fig. 9). Transition unions allow thermal movements between metal and plastic without leaks. Use a male-threads adapter for non-pressurized connections at spots such as shower risers and water heater relief valve tappings. Some mechanical couplings made for PB water supply tubing also work with copper tubing since the two are the same size. These allow you to joint plastic to copper without sweat-soldering. These fittings make effective transition unions. Flexible fittings. Flexible replacement drain-waste-vent and sewer/drain pipe fittings are made of soft vinyl. These come with large worm-drive band clamps that enable them to be fastened securely to plastic or metal pipes. A flexible fitting can be shoehorned into place, even though the pipes it fits over are immovable.

FIG. 10 - Don't bind plastic pipes in. They need room to expand and contract.

INSTALLING PLASTIC PIPING Plastic piping is the easiest to install, but there are special things to look for. Securing. Mount plastic pipes so they can expand and contract without damage. Larger DWV pipes are hung by perforated metal strapping called "plumber's tape" spaced a maximum of 48" apart. Smaller water supply tubes are attached to the framing by tubing hangers that hold it tightly to the framing while permitting back-and-forth movement. Use hangers a maximum of 32" apart (one hanger at every other joist). Also, be sure not to bind rigid pipes in at the ends. Leave about 1/4' for every 10' of pipe, as shown in Fig. 10. Provide protection from nails with pre-punched, nailed-on steel straps from your dealer. The straps also help to brace over any notches made in the framing for piping. Be sure to install air chambers or water hammer arresters at every fixture and appliance except toilets. Joining to existing drain. To lead a new drain into an older plastic drain, use slip couplings. First, mark the portion of the old pipe to be cut out where the new pipe will join it. Next, saw out the length of pipe between the marks. Slide a shoulderless slip coupling onto both ends of the cut pipe, leaving about 1-1/2" exposed for solvent welding. Position the new fitting ready for coupling onto the old pipe. There will be pipe stubs on both sides of the joints for solvent welding. Dope the pipe ends all around with a heavy coating of solvent cement. Immediately slide the slip coupling into place, halfway astride the joint. Give it a slight twist as you put it in place. Hold the alignment for 10 seconds before working on the other end of the fitting in the same way. Direct burial. When plastic sewer and drainage pipes are buried in the ground, follow a few common-sense rules. First, lay the pipes on unexcavated trench bottom, not on soft fill. Fill could settle unevenly, making low spots in the pipeline. Dig out depressions for the couplings so that lengths of pipe are fully bedded, not bridged between couplings. Backfill around the pipes should be free from rocks that could damage the pipe walls. Packed sand is a good initial backfill. Once the pipes are well covered, use ordinary backfill the rest of the way. TABLE B   Choosing a Cement Type of Cement Type of Pipe   ABS PVC CPV Styrene All-Purpose ABS R R R R R PVC NR R R NR R CPVC NR NR R NR R Styrene R R R R R R-Recommended   NR-Not Recommended