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Fix-It-Yourself Project #105
"How to Work With Plastic Piping"

Tool and Material Checklist

Pipes, Tubes, Fittings, Solvent cement, Cleaner/primer, Fine tooth saw, Miter box, Knife, Paint brush, Clean cloths, Teflon plumber's tape, Plastic pipe cutter, Screwdriver, Nut-driver, Channel-locking pliers, Flaring tool, Silicone rubber sealant (RTV) or plumber's putty, Hand cleaner

1. Descriptions of various types of plastic pipe

Plastic (more correctly thermoplastic) for plumbing comes two ways: in pipe sizes and in tubing sizes. While both these 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, cannot be interchanged. With plastic piping you choose from among a wide selection of materials.

Rapid technological advances may leave local plumbing codes behind the times. 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 house fixtures and to vent the system above the roof. Sewer pipes are made for carrying household wastes below ground to a public sewer or private disposal system.

Drainage pipes are for below-ground use, too, but are thinner-walled and thus lower in cost. They're usually for use 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 will withstand hot water under pressure: rigid CPVC and flexible PB. The two may be used singly or together to build corrosion-free, nonelectrolytic household water supply systems. Because plastic pipe is nonconducting, 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 between a water supply system and faucets, making the faucets easier to concoct. 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 Material (ASTM). Look for the ASTM designation on each pipe, tube, and fitting that you buy. This signifies 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.

2. Solvent Welding

The simple solvent-welding process used to join many plastic pipes should be done properly to prevent getting leaks. Here's how.

Use the two-step method (employing cleaner/primer and solvent), except with ABS and styrene on which the one-step method (using 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 good material. A damaged fitting should be discarded.
  2. Unless both the pipe and the fitting are made by the same manufacturer (a very good idea to look for when purchasing), test-fit them. The pipe should enter the fitting, but meet resistance part-way in. Held upside down, it should hold on and not fall off.
  3. Cutting pipes. Cut the pipe off squarely to 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 lots 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. Do not sandpaper plastic pipes. It may remove too much material for successful joining.
  4. Cleaning. Using a quality cleaner/primer, clean the pipe end and fitting socket. (Omit this entire step with ABS and styrene.) Apply cleaner/primer with a dauber, brush, or clean cloth to remove grease, oil, 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 that the solvent cement to be of the right type.
  6. Liberally apply cement first to the pipe end and then apply it sparingly to the fitting socket. Leave no bare spots. With chemical-resistant PVC and CPVC pressurized piping, it's a good idea to give the pipe two applications of cement, one before and one after coating the fitting socket. With all solvent welding, the dauber or brush used to apply cement should be at least one-third to one-half the pipe's diameter.
  7. Immediately join pipe and fitting full depth, with a slight twist that brings it to correct alignment. The twist breaks up insertion lines in the solvent cement. Hold the fitting on until the solvent cement grabs tightly. The fillet of cement around the fitting indicates that enough solvent cement was used 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 prolong breathing of solvent cement and cleaner/primer vapors. For this reason, it's best to work in a well ventilated area. Cap the cans after each use. And keep solvent and cleaner away from any open flame. The precautions appear on the labels. Read and follow them. Cement on your hands may be removed 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. Thus when you accidentally put the wrong fitting on a pipe, you must cut it out and replace it with the correct fitting.

3. 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, figure 6. Position the clamp about 1/4 inch 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, diminish or completely shut off water flow.

PB tube. 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, often not interchangeable with those 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. Flaring is done with a flaring tool. To prevent cracking of a CPVC tube when flared, the end should be cut off squarely and smoothly, preferably with a pipe or tubing cutter. It helps to soak a rigid tube's end in boiling water just before flaring.

Slip-jam-nut couplings. Tubular drainage pipes are joined by slip-jam-nut coupling. 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 inside 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.

Most plastic tubular couplings will tighten leak-free by hand, but it doesn't hurt to five 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, a fitting called a transition union should always be used. Transition unions allow thermal movements between metal and plastic without leaks. A male-thread adapter may be used for nonpressurized concoctions 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 permit joining plastic to copper without sweat soldering. These fittings serve as 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 let them be fastened securely to plastic or metal pipes. A flexible fitting can be shoe-horned into place even though the pipes it fits over are immovable.

4. Installing Plastic Piping

While it is the easiest of all to install, plastic piping has needs all its own.

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 inches apart. Smaller water supply tubes are attached to the framing by tubing hangers that hold it tightly to the framing, yet permit back-and-forth movement. Use hangers 32 inches apart maximum (one hanger at every other joist). Moreover, be sure not to bind rigid pipes in at the ends. Leave about 1/4 inch for every 10 feet of pipe.

Provide protection from nails with prepunched 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.

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-inch 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 do. Hold the alignment for 10 seconds before working on the other end of the fitting ins the same way.

When plastic sewer and drainage pipes are buried in the ground, a few common-sense rules should be followed. First of all , 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 might damage the pipe walls. Lacking good on-site materials, packed sand makes a fine initial backfill. Once the pipes are well covered, ordinary backfill may be used the rest of the way.