Plastic piping and do-it-yourself plumbing go together like hammers and nai= ls. Plastic pipe is easy to cut and join to its many fittings, and it is wi= dely accepted by plumbing codes. Inside this document you will find informa= tion about:
=E2=80=A2Meet the Plastics =E2=80=A2Solvent Welding =E2=80=A2Mechanical Couplings =E2=80=A2Installing Plastic Piping =20
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 ins= ide 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, sh= ould not be interchanged. With plastic piping, you choose from a wide selec= tion of materials. Table A shows the plastic plumbing materials available a= nd describes what each is used for.
Rapid technological advances in plastic plumbing may leave local plumbing c= odes outdated. So, before purchasing your materials, it=E2=80=99s a good id= ea to consult your city or county building officials.
DWV stands for the drain-waste-vent system used to carry wastes away from y= our home=E2=80=99s fixtures and to vent the system above the roof. Sewer pi= pes are made to carry household wastes below ground to a public sewer or pr= ivate disposal system. Drainage pipes are used below ground, too, but are t= hinner-walled and lower in cost. They=E2=80=99re usually used with non-sept= ic water, such as roof runoff. Tubular goods are the thin-walled fixture dr= ain and trap parts used beneath sinks and washbasins.
Only two kinds of plastic tubes can withstand hot water under pressure: rig= id CPVC and flexible PB. The two may be used singly or together to build co= rrosion-free, non-electrolytic household water supply systems. Because plas= tic 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 use= ful as deep-well pipe.
Riser tubes are the highly flexible, small-diameter tubes linking a water s= upply 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 Amer= ican Society for Testing and Materials (ASTM). Look for the ASTM designatio= n on each pipe, tube and fitting that you buy, signifying that it meets AST= M standards. Water supply piping should carry the National Sanitation Found= ation=E2=80=99s =E2=80=9CNSF-pw=E2=80=9D approval, meaning the parts are su= ited for carrying potable, or drinkable, water. =20
SOLVENT WELDING
The simple solvent-welding process used to join many plastic pipes must be = done properly to prevent leaks. Here=E2=80=99s how.
Use the two-step method=E2=80=93employing cleaner/primer and solvent=E2=80= =93except with ABS and styrene, with which the one-step method (solvent onl= y) is usually enough.
- Inspect the pipe end and fitting socket for cracks, gouges, dirt and abr= asion. If the pipe end is imperfect, it can be cut back to expose good mate= rial. Discard a damaged fitting.
- It=E2=80=99s a good idea to purchase pipe and fittings made by the same = manufacturer. If this isn=E2=80=99t the case, test-fit them. The pipe shoul= d enter the fitting but meet resistance part-way in. Held upside down, the = pipe should not fall off.
- Cutting pipes. Cut the pipe off squarely to the proper length using a fi= ne-tooth saw or plastic pipe cutter (a hacksaw works well). Flexible plasti= c pipes are more easily severed with a sharp knife, but be careful not to c= ut yourself. If you have a large amount of cutting to do, you can get a tub= ing cutter with a special wheel for use on rigid plastics or a shear-type c= utter for PVC. Then, using a knife, remove any burrs and chamfer the outer = end of the pipe slightly. Do not use sandpaper on plastic pipes. It may rem= ove too much material for successful joining.
- Cleaning. Now, using a quality cleaner/primer, clean the pipe end and fi= tting socket (omit this entire step with ABS and styrene). Apply the cleane= r/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 pip= e should be dry before applying cement.
- 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, then apply it sparingly to th= e fitting socket. Leave no bare spots. With chemical-resistant PVC and CPVC= pressurized piping, give the pipe two applications of cement=E2=80=93one b= efore and one after coating the fitting socket. With all solvent welding, u= se a dauber or brush that=E2=80=99s at least one-third to one-half the pipe= =E2=80=99s diameter to apply the cement.
- 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 solv= ent 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. =E2=80=A2Safety precaution. Avoid prolonged breathing of solvent cement and= cleaner/primer vapors. Work in a well-ventilated area, and cap the cans af= ter each use. Keep solvent and cleaner away from any open flame. Read and f= ollow the precautions that appear on the labels. Remove any cement on your = hands with hand cleaner.
=E2=80=A2Correcting errors. Solvent welding is normally a one-way process= =E2=80=93you 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. MECHANICAL COUPLINGS
Some fittings are made for joining pipes and tubes that cannot be solvent w= elded.
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 o= ver the pipe end and push the pipe all the way onto the barbed fitting. Pos= ition the clamp about 1/4=E2=80=B3 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 syste= ms is joined by patented O-ring-sealed mechanical couplings. Each system us= es its own coupling, and they=E2=80=99re often not interchangeable with tho= se of other systems. Follow the instructions for the kind you are using.
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. F= laring 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=E2=80=99s end in boiling water just before flaring.
Slip-jam-nut couplings. Tubular drainage pipes are joined by slip-jam-nut c= ouplings. To make up such a coupling, first install the nut facing its thre= ads. Then install the correct-sized slip washer with its flat face toward t= he nut. If you are sure that none of the parts are made of ABS plastic, whi= ch is adversely affected, you may use plumber=E2=80=99s putty or silicone r= ubber sealant around the inside of the slip jam nut to prevent leaks. Adjus= t the length and direction of the tubular parts, then start the nut=E2=80= =99s threads with its fitting and tighten.
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 plie= rs.
Transition unions. For adapting plastic water supply tubing to threaded met= al parts, such as at water heaters and bathtub/shower valves, use a fitting= called a transition. Transition unions allow thermal movements between met= al and plastic without leaks. Use a male-threads adapter for non-pressurize= d 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 co= pper tubing since the two are the same size. These allow you to joint plast= ic to copper without sweat-soldering. These fittings make effective transit= ion unions.
Flexible fittings. Flexible replacement drain-waste-vent and sewer/drain pi= pe fittings are made of soft vinyl. These come with large worm-drive band c= lamps 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 fi= ts over are immovable. INSTALLING PLASTIC PIPING
Plastic piping is the easiest to install, but there are special things to l= ook for.
Securing. Mount plastic pipes so they can expand and contract without damag= e. Larger DWV pipes are hung by perforated metal strapping called =E2=80=9C= plumber=E2=80=99s tape=E2=80=9D spaced a maximum of 48=E2=80=B3 apart. Smal= ler water supply tubes are attached to the framing by tubing hangers that h= old it tightly to the framing while permitting back-and-forth movement. Use= hangers a maximum of 32=E2=80=B3 apart (one hanger at every other joist). = Also, be sure not to bind rigid pipes in at the ends. Leave about 1/4=E2=80= =B2 for every 10=E2=80=B2 of pipe, as shown.
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 fr= aming 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 t= he marks. Slide a shoulder-less slip coupling onto both ends of the cut pip= e, leaving about 1-1/2=E2=80=B3 exposed for solvent welding. Position the n= ew fitting ready for coupling onto the old pipe. There will be pipe stubs o= n both sides of the joints for solvent welding. Dope the pipe ends all arou= nd with a heavy coating of solvent cement. Immediately slide the slip coupl= ing into place, halfway astride the joint. Give it a slight twist as you pu= t it in place. Hold the alignment for 10 seconds before working on the othe= r end of the fitting in the same way.
Direct burial. When plastic sewer and drainage pipes are buried in the grou= nd, follow a few common-sense rules. First, lay the pipes on unexcavated tr= ench 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 p= ipes should be free from rocks that could damage the pipe walls. Packed san= d is a good initial backfill. Once the pipes are well covered, use ordinary= backfill the rest of the way.
...................... John Frantzen is a Master Contractor and a respected editorial columnist fo= r several news-groups and on-line resources. He has over 25 years direct h= ands-on experience in the construction and home renovation industry.