Working with Pipe: Plastic Pipe

Home | Wiring | Plumbing | Kitchen/Bath

If your local building or plumbing code permits, plastic is the material to choose for any new installation or addition to your plumbing system. It is lighter to move and carry about and much easier to join than any of the metal pipes. You use a solvent cement or compression fittings and the joints are just as permanent and water tight as any metal piping. You don’t need expensive special tools or have to use potentially hazardous flame or molten metal.

Plastic can be cut with almost any saw or a tubing cutter. The flexible plastic pipe can be cut with a knife. Because plastic is chemically and electrically inert, it can be used in the same system with iron or copper without the threat of galvanic action. And it will not rust or corrode. Because it's so smooth inside and chemically inert. it will not collect mineral deposits as readily and clog up like metal. Another very good reason to use plastic is that it's less expensive than any metal.

On the negative side, plastic is prohibited for water supply systems in many localities. Some say that's be cause plastic would melt or burn in a fire, others say it hasn’t been around long enough to be proven, and still others say labor unions oppose it on the grounds that it takes far fewer hours to install and would provide fewer jobs. In any case, if your local code prohibits plastic pipe, don’t use it. The building inspector could make you re move it all and replace it with pipe that does meet the code.

Plastic pipe has other disadvantages. Plastic pipe or fittings can't be used to support the weight of a fixture. Also, plastic expands considerably and tends to soften and sag when exposed to hot water for an extended period and not supported. Closely spaced, loose-fitting supports will solve this problem satisfactorily. Plastic must be protected, like copper, from mechanical damage such as errant nails and heavy objects.

Pipe and Fittings

Plastic pipe commonly used for plumbing is made out of four different kinds of plastic: PVC (polyvinyl chloride), CPVC (chlorinated polyvinyl chloride), ABS (acrylonitrile-butadine-styrene), and PB (polybutylene). PVC and CPVC are rigid, white or sometimes pastel plastics. CPVC, the newer of the two, is best when you want plastic hot- water pipes. It is, of course, also used for cold-water piping. ABS is rigid, black or gray plastic used primarily for drain, waste, and vent systems. PVC is also widely used for DWV systems. Most codes specify that pipe and fittings of different plastics (like ABS and PVC) can't be mixed in the same system. The newest member of the group is PB pipe. It is flexible, black or dark gray, and more costly than the others. It can't be joined with solvent cement but requires compression fittings. PB, now used mostly in irrigation systems and by gas and water companies for service mains, isn't well known or readily available to the homeowner. However, because of its flexibility and strength, it's rapidly gaining acceptance for residential use. PB has good heat resistance and is approved for hot-water lines.

Plastic pipe comes in all the same nominal diameters as iron and copper pipe, and there are adapter fittings to connect plastic pipe to a metal system. In addition to the adapters, plastic pipe has all the same f it tings as metal pipe.

Plastic Fittings: Bushing, Cap, Female adapter, Male adapter, Coupling; Adapter ell; 90-deg. Ell; 90° street ell; Reducing ell; Sanitary tee; Slip-joint coupling; Disassembled union

Ill. 39 Working with Pipe: Cutting and Joining Plastic Pipe

Measuring, Cutting, and Joining

Plastic pipe is measured and cut the same way as cop per pipe. You measure the distance be tween the laces of the fittings and add the length of pipe that will go into the fittings. Plastic pipe is so light and easy to maneuver that you can often just cut and slip together several sections of pipe and fittings to be sure it fits the way you want it, and then go back and cement it all together at once.

The actual cutting is done just like with copper tubing. But the cutting wheel for copper tubing is usually not sharp enough and just creases the plastic. You can use a tubing cutter that has been adapted for plastic pipe. If you want to use a saw. a hacksaw is probably best, but a coarser blade works better on plastic than the 3 2-teeth- per-inch recommended for copper tubing, In fact, al most any wood saw works quite well on plastic pipe. Be sure to remove burrs and rough edges with a knife or file before joining the pipe.

To join plastic pipe, you must use the solvent cement made for the kind of plastic you are using. ABS solvent will not work well on PVC pipe, for instance. The proper solvent actually melts the plastic of the pipe and fitting and “welds” them together. making the joints very solid and permanent.

Solvent cements are classified as both airborne contaminants and flammable liquids. Be sure to use them only in a well-ventilated area. If you must join pipe in an enclosed space. use a fan to provide ventilation and take frequent breaks to breathe clean air. Keep the container tightly closed when you’re not actually using the solvent and keep the solvent and its container away from all sources of ignition, heat, sparks. and open flame.

When the pipe is all cut and ready to join, inspect both the end of the pipe and the fitting to be sure they are smooth and perfect with no deep cuts, cracks, or rough edges. Use some fine sandpaper or some specially prepared plastic pipe cleaner to remove the gloss and any moisture or oil from the joint surfaces. Brush a light coat of solvent cement on the outside of the pipe and inside the fitting. Then quickly brush a second coat on the outside of the pipe, push the pipe into the fitting as far as it will go. and give it a quarter turn to evenly distribute the solvent. A small bead of solvent should be visible all around the joint.

If the direction of the fitting on the pipe is critical, mark both pieces with a pencil or small knife cut before you apply the solvent (see the drawing). Line up the marks quickly after giving the pipe its quarter turn. Once the plastic hardens, it's a permanent joint and can't be adjusted.

Hold the joint together for 10 or 15 seconds to be sure it's set solidly before you move on to the next joint. Wait at least an hour after you’ve made the last joint before you test the system. In fact, it’s better to let the plastic set overnight before you turn on the water.

Cut the pipe, remove any rough edges with a knife, and finish off with sandpaper.

Brush a coat of solvent cement on the outside of the pipe and inside of the fitting.

As soon as you have put the second coat on the outside, push the pipe all the way in and twist it a quarter turn.

Ill. 40. Fixing Leaks in Plastic Pipe

Repairing Plastic Pipe

For a pinhole or small leak, turn oft the water, drain the pipe, and let it dry for a few hours. Force some plastic solvent cement into the hole and wrap the area tightly with plastic electrical tape,

For a larger hole or damaged pipe, cut out the bad section and if there is enough play in the system, rejoin the pipes with a coupling. If there isn’t any play, use two couplings or a coupling and a plastic union to add a section of pipe the same length as the piece that you cut out.

If you have a leaky joint, you can try smearing or forcing solvent cement into the joint, but this doesn’t usually work. The best solution is to cut the pipe a couple of inches on each side of the joint and install a new joint and short sections of pipe with couplings (see the drawing).

Tools for Working with Plastic Pipe

Tubing cutler or saw. A tubing cutter designed for plastic pipe works best. The cutting wheel designed for cop per tubing will not cut the plastic satisfactorily. Almost any saw will cut plastic pipe. Those with fine teeth, like a hacksaw, work best. When cutting plastic pipe with a saw, be sure that the cut is at a precise right angle, A small miter box is useful for this purpose. Also be sure to clean off all the burrs and smooth the edges of the plastic with a knife or sandpaper before joining. Solvent cement. You must use the proper solvent cement for each pipe—for example, PVC cement for PVC pipe and ABS cement for ABS pipe. The cement usually comes with a brush or dobber attached to the lid of the container for easy application.

Solvent cement; Cut out the damaged area; pull the ends together. If the ends won’t pull together, use a short length of new pipe and join with a coupling. Replace a leaky fitting by cutting the pipe on each side of if...and two couplings; and cementing in a new fitting, pipe, and couplings,

New pipe; Coupling; Old pipe; Plastic Pipe Tools; Tubing cutter; Pocket knife; Sandpaper

Sunday, May 13, 2012 0:18 PST