If you’re doing any remodeling or repair work on the plumbing system of an older home, it’s a pretty safe bet that you’ll encounter the need to transition from an older type of pipe to a one of today’s newer materials. It might be a transition from threaded galvanized water pipes to copper pipes, or from old cast-iron sewer lines to today’s ABS.
Luckily for all of us, these transitions are common enough that there are a number of fittings on the market that make dissimilar pipe connections quick, easy and safe. The fittings are readily available in home centers, hardware stores and plumbing supply retailers.
COPPER PIPE TO THREADED STEEL PIPE
If you’ve browsed through the plumbing section at the home center, you no doubt noticed that there are threaded copper pipe fittings that you can solder right onto the end of the pipe, and they will screw directly onto older threaded galvanized water lines. So what’s the problem?
The problem is that the zinc used for galvanizing the threaded water pipes doesn’t get along very well with the copper. If you make a direct connection, these two materials will interact in a chemical reaction that will corrode the joint and eventually cause it to start leaking.
To safely connect copper and galvanized steel, you have two options. Since brass doesn’t react with either the copper or the zinc, one method is to make sure you have a threaded female end on both the copper and the steel pipes, and then connect the two by simply inserting a short threaded brass nipple between them.
The second method is to use a special transition fitting called a dielectric union. The dielectric union has a threaded steel female fitting on one end, which is threaded onto the steel pipe. The other end has a female copper slip (non-threaded) fitting, which is soldered onto the copper pipe. The two halves of the joint are then connected using a lock nut and two insulating washers that prevent the copper half from contacting the steel half. The fittings cost under $10, and not only is the transition easier to accomplish, but it also leaves you with a joint in the line that can be disassembled later if you need to perform other work on the lines.
PLASTIC PIPE TO COPPER OR STEEL PIPE
Making the connection between plastic pipes such as ABS or PVC and metal pipes such as copper or galvanized steel is very straightforward. The chemicals used in the manufacture of any of these pipes do not react with one another, so you don’t have the corrosion factor to worry about.
The connection between plastic and metal is simply a matter of choosing a threaded fitting of the proper size and configuration to make the transition. Remember that copper pipe will need to have a threaded male or female fitting soldered onto the end first.
For example, suppose you’re installing a new sink and you want to use a 1 1/2-inch ABS trap connected to the 2-inch female-threaded steel pipe that’s currently in the wall. Plastic pipe fittings are available as either threaded (both male and female threads are available) or slip (non-threaded for making glue joints). First, select a 2-inch ABS fitting with a male thread on one end and a female slip joint on the other, and screw the fitting into the existing steel pipe. Glue a 2-inch male x 1 1/2-inch female transition fitting into that, then glue in your 1 1/2-inch trap.
When making plastic-to-metal transitions, wrap the threads with Teflon tape to help seal the joint and also to make it easier to assemble. Don’t use pipe dope on these connections, as it can deteriorate the plastic. Also, two windings of tape will be sufficient to make the seal — more layers can stress the joint and actually cause it to leak.
PLASTIC PIPE TO CAST-IRON PIPE
Transition fittings are also commonly available to adapt ABS pipe to cast iron. Called a band clamp, the fitting is simply a thick rubber tube with a screw clamp on each end. To use the fitting, slip one end over the outside of the cast-iron pipe and the other end over the plastic pipe, then use a screwdriver to tighten down the clamps on either end.
These are just a few examples of the hundreds of transition fittings that are available. Simply determine the type and size of the pipes you’re trying to connect, and your dealer can help you select the best type of fitting for the job.
Remodeling and repair questions? E-mail Paul at [email protected].
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