When your plumbing pipes spring a leak, it can quickly develop into an emergency, and the repair can be more complicated if you don't have a way to shut off the water. To avoid having to call a plumber to find and shut off the main water supply in such a situation, it's a sensible move to install accessible shut-off valves on your main water supply and on important branch lines. If your pipes are plastic or copper, the procedure is straightforward and not time-consuming, but if they are galvanised metal, it involves some disassembly.
Turn off the main water valve and cut out a 12-inch section of pipe with the hacksaw at the location where you want to install the shut-off valve. Let the water drain out and de-burr the ends of the pipes with a flat metal file.
Glue plastic couplings to the ends of the pipes with PVC cement. Spread glue on the ends of the pipes and on the insides of the fittings with the brush that comes with the cement and slide the fittings on. The glue will set in less than a minute.
Measure and cut two lengths of plastic pipe that will extend from each coupling to the end of the valve, allowing an extra 1/2 to 3/4 inch at either end to go inside the fittings. Glue the pipes to the couplings.
Glue the shut-off valve to one of the pipes and let the glue set for about a minute. Pull the pipe and the valve toward you until they are far enough apart for the pipe to slide into the fitting. Spread glue on the outside of the pipe and the inside of the fitting and insert the pipe. Push them away from you so that the pipe seats securely inside the fitting.
Turn off the main water valve and cut out a 12-inch section of pipe at the location of the valve with a hacksaw. Let the water drain completely, then de-burr the ends of the pipes with a flat metal file.
Spread plumbing flux on the ends of the pipes and on the insides of two copper couplings and slide the couplings onto the pipes.
Cut two lengths of copper pipe with a hacksaw that will extend from the couplings to the openings of a brass shut-off valve, adding 1/2 inch at either end to go inside the fittings and the valve. De-burr both ends of both pipes and spread flux on the outsides. Spread flux on the insides of the couplings and the valve and assemble the pipes with the valve installed in the middle.
Heat each joint in turn with a propane torch until the flux begins to spit and smoke. Remove the torch and touch the end of a coil of lead-free solder to the heated metal around the joint, moving it around the pipe as it melts and wicks into the joint, fusing the metal.
Turn off the water and cut out a 4-inch section of pipe with a hacksaw. Unscrew the ends of the pipe you have cut from the fittings to which they are attached with two pipe wrenches. Hold the fitting with one wrench while you turn the pipe with the other.
Screw a galvanised nipple, which is a short length of pipe that is threaded on both ends, into one of the fittings and screw a threaded steel shut-off valve to the other end of the nipple. Screw a second nipple into the other end of the valve. Nipples are available in various lengths.
Measure the distance from the end of the nipple in the valve to the remaining fitting from which you removed the pipe. Go to the hardware store and have them cut you a length of pipe to that length and thread it on both ends. You can cut and thread the pipe yourself, but since it requires the rental or purchase of a pipe threader, it's easier and less expensive to have it done at the hardware store.
Separate a galvanised steel union. Screw one half to one end of the pipe you measured and the other half to the end of the nipple attached to the valve. Screw the other end of the longer pipe into the fitting, then join the pipes by screwing the union together with a pipe wrench.
Prepare PVC pipes so that you can quickly join them after you spread the glue.
Drain water completely from copper pipes before attempting to solder them. If any water is standing in the lines, it will absorb the heat from the torch and prevent the pipes from getting hot enough to melt the solder.