Replacing Valves along with Faucet
If you have opted to replace your valves at the same time you replace the faucet keep reading; otherwise skip to the next page. Be certain to turn off the water where it comes into the house as described on the previous page. Replacing a valve on plastic pipe is a simple matter of unscrewing the old valve then screwing on a new one. Or if you did not have a valve in the first place, you can simply cut the pipe where you wish to put the valve, glue on a threaded coupling and then affix the new one.
Connecting to an existing 3/8 inch supply line is also fairly simple. Get a valve with a compression ring that fits the appropriate size pipe. Remove the compression ring and nut from the valve. Put the valve on the pipe so that it faces toward the cut end. Then push the compression valve onto the pipe. Now join the nut to the valve. The compression ring will tighten as you tighten the nut with a wrench to the point that it makes a perfect seal.
More difficult, is affixing a valve to a copper pipe. A threaded coupling must be soldered to the pipe. If you have no experience soldering in tight places you might want to leave this bit to a professional. But if you are game enough to try it yourself, you will need a propane torch, flux, plumber's sand cloth, a round wire fitting brush and solder (I recommend the lead-free solder). A piece of fire resistant Kevlar will also prove handy in this situation. When soldering a joint, be sure first to smooth the rough edge of the copper pipe with a file, then rub the last inch with the sand cloth. You will then want to use the wire brush inside the fitting where the pipe and the fitting come together.
Spread flux on both the end of the pipe and inside the fitting. Join them together the way you want them to fit. Don't worry that the fitting is sitting on top of the pipe. The flux and the job you did with the cloth and wire brush will work some magic and actually suck the solder (when it melts) up into the joint. Now use your Kevlar to protect anything that might catch fire or melt. Start up your torch and get yourself a little blue flame. Direct it on the pipe, near the joint. Do not touch the pipe with your bare hands (even quite distant from the heat point it will get hot). Uncoil some of your roll of solder and while heating the pipe push it against the place where the pipe and the fitting meet. If the metal is hot enough the solder will melt and immediately get sucked into the joint. Do not put your flame directly on the solder. It will simply drip if the metal itself is not hot enough to do the job.
Once the solder is in the joint, let the fitting cool before twisting on the valve. (Be sure to use plastic tape for this joint to prevent leakage and corrosion.)