A Primer on Plumbing Pipes

Some time in the past 30 or 40 years, I remember an initiative to get truth in advertising. I don’t know how successful it was, but one industry that apparently wasn’t affected by it is the plumbing industry. I can’t think of any other industry that has as many definitions for what a 1/2″ or any other size pipes are. 

One would think that 1/2″ copper tubing would be the same, no matter what, but the sad truth is that 1/2″ rigid copper pipe has a different outer diameter ( OD), then 1/2″ flexible copper pipe. Fittings for one will not work on the other. If you want to use both you would have to purchase an adapter. The same thing can be said for plastic pipe, a piece of 1″ black ABS pipe is not the same size as 1″ white PVC plastic pipe. Again to use both, a home owner would need a buy an adapter.

To help eliminate some of the confusion, here is a primer on plumbing fittings and connections.

Rigid Copper Pipe:

Used mostly for hot and cold water lines within the house. The best tool to cut rigid copper tubing is a pipe cutter. The pipe is placed in the cutter, and the knob is turned down, which brings the pipe into contact with the cutter wheel. As the cutter is rotated around the pipe, you continue to tighten the wheel, until you have cut through the entire pipe.

There are two ways to connect copper pipes together. The first is to   solder  or sweat the pipes together. The second is the use of compression fittings.  Soldered  fittings are much less expensive then the compression, but take a little more work to make a leak free joint.

When you sweat copper pipes, the first thing is to clean the ends that you are going to sweat together. then flux is applied to both the pipe and the fitting you are connecting to it. The pieces are placed together, and heat is applied to the union with a propane torch. When the union is heated enough,  solder  is applied to the joint, the  solder  is sucked into the joint, sealing the two pieces together. From experience, I can tell you take to make this work successfully, there must be absolutely NO WATER in the line, if there is the joint will leak. And once a joint leaks , there is no repairs without replacing the fitting and starting over. Professional plumbers tend to use a hotter source of heat, then the propane bottle can provide. But I’m always concerned about using any heat source inside my house. If you choose this method, be very careful with the torch in tight spaces. It might be a good idea to have a fire extinguisher handy.

Compression fittings do not require heat. A common place that compression fittings are used is at the water shut off valves beneath your sink, or toilet. But there are many other places that you can use them. To make up a fitting using a compression fitting, start by cutting the inlet pipe to length, using a pipe cutter. Place the compression nut and compression ring over the end of the pipe, as shown above, then insert the pipe into the compression seat. Then using two wrenches, one to hold the fitting and the other for the compression nut, tighten the compression nut completely. This forces the compression ring unto the pipe, creating a water tight seal.

Compression fittings are not fool proof. If the pipe is not seated all the way onto the seat, the joint will leak, thus it is imperative that the end of the pipe be cut flat. Compression fitting are designed as a one use only device, if it leaks cut out the offending piece and start over again. Also the pipe must be completely cleaned before you start, any dirt or corrosion on the pipe will create leaks. Tightening the compression nut in confined spaces may require to use of special tools like crows feet wrenches.

Flexible Copper Pipe:

This is used mainly to connect natural or propane gas to your house. It is normally connected to the appropriate devices with the use of compression fitting designed for the flexible pipes. Flexible copper pipe is suitable for being installed under ground. Flexible copper pipe may look like a great choice for indoors plumbing runs, but it is not recommended for that use. Also the limited amount of fittings available make this a less then perfect choice. Flexible copper fitting are NOT interchangeable with fittings for rigid copper pipe.

Some professional plumbers are currently installing flexible water pipes, but these require special tools and fittings, that are not available to the DIY’r. Not all municipalities allow for the use of flexible pipes for water delivery with in the home.

Rigid Pipe:

This pipe comes in either black iron or galvanized pipe. Black iron pipe is normally used to run natural gas inside the home, while galvanized is used mainly for water lines. The ends of these pipes are threaded, as are the connecting pieces. You simply screw the pieces together, after applying either plumber’s tape or pipe dope.

Plumber’s tape is made of Teflon, and is white in color. You should apply it to the male end of the pipe, by running the tape around the pipe several times. Install the tape in the opposite direction, then the male end of the pipe will thread into the female union. Before you thread the two pieces together, be sure to clean out any remaining Teflon tape on the inside of the female threads if you are re using the fitting. There is a Pink Teflon tape, that used solely for making up connection is natural gas lines. Pipe dope, is actually a thick paste that is applied to the threads using a brush. If you are reusing a fitting that has had pipe dope applied before, you must clean both the male and female threads, using a wire brush and a pick, much like the ones that the dentist uses to clean our teeth.

To connect two pieces of pipe together or to install an adapter or fitting, use two pipe wrenches. The first wrench is used to hold the pipe, while the second one is used to turn the fitting or adapter. While you may not use a pipe wrench all that often, this is not the place to go for the bargain priced tool. Sometimes it takes considerable energy to loosen a threaded joint that has been in place for several years. The cheaper wrenches tend to slip, which can cause injury to you or cause damage to you home.

Recently galvanized pipes have gotten some bad press, when used for water delivery. Apparently the insides of the pipes are releasing chemicals into the drinking water, so it is advised that you stick to either copper or the newer flexible pipes for water delivery.

Plastic or PVC/ABS Pipes:

PVC ( Polyvinyl Chloride) pipe is a white plastic pipe that is used to supply both hot and cold water to the interiors of many homes. This product is very flexible and easy to use. There are two ways to cut PVC pipe, either use a hand saw or miter saw to cut large diameter pieces. Smaller diameter pieces can be cut using hand held PVC cutters. To connect PVC pieces, you first cut the pipe to length, then using a cleaning solution designed for the pipe, clean both the ends of the pipe and the connecting piece. A special glue is then applied to both pieces, and the pieces are pushed together. The glue sets, within a minute, so it is vitally important that the pieces be aligned properly when pushed together. There is a very limited amount of time that you can maneuver the pieces. It is a very good idea to use a scribe line to indicate to proper orientation of two mating pieces.

ABS ( Arcylonitrile Butadiene Styrene) is a black plastic pipe that is used for drain, waste and vent (DWV) plumbing in today’s homes. This product replaced the cast iron pipes found in many older homes. ABS is worked in much the same manner as the PVC pipe. It can be cut with hand saw or powered miter saw. It uses a cleaner and glue similar to the PVC pipes, only this is designed for the ABS pipes.

When you are gluing either of these products, it is recommended that you use a pair of disposable gloves to protect you hand, unless you like picking dried glue off your hands for several days. Also it is recommended that you work in a well ventilated area.

Generally, you will not see both white and black plastic pipes connected together. One exception to this is maybe found under the sink. A lot of manufacturers are making “P” traps, shown here in black ABS, for the sink drains out of white plastic.

Because of its flexibility you may find homes in earth quake areas plumbed with PVC rather then the conventional rigid copper pipes. There was a lot of bad press in the 90’s about PVC pipes breaking within the walls of homes, this was traced to specific manufacturers, and shouldn’t be seen as a condemnation of the product.

The PVC and ABS pipes are not sized the same. a 1 ” PVC will not connect to a black 1″ ABS fitting. This may have been done to keep us from inadvertently using the wrong pipe for the wrong application, but it sure is confusing. I mean a 1″ pipe should be a 1″ pipe.

I hope this helped clear up some of the confusion about the many options offered to us by the plumbing manufacturers. A word of advice learned the hard way, check to be sure that all your fittings do actually connect before you leave the store or you may find yourself making return trips to your DIY store as I’ve done many times.