Clamp locking pliers to the old soldered valve and heat the valve with a propane torch. When the solder melts, twist the valve back and forth while pulling it off. Wipe the end of the pipe with a cloth immediately after removing the valve to get rid of old solder. (Wear a glove so you don't burn your hand.)
Slide the compression nut, then the ferrule, onto the copper water pipe. Lubricate the compression threads with a small amount of pipe dope. Tighten until firm with a pair of adjustable wrenches and then turn the wrench an additional 180 degrees. Reconnect the faucet supply line after the shutoff valve is in place.
Old shutoff valves often develop leaks when you shut them off to install or repair a plumbing fixture. Whenever you replace or work on a fixture, check the shutoff valves and replace them if they look old or are hard to turn. Turn off the water at the water main. Open a basement faucet and the faucet above your shutoff valve. We show you how to replace a shutoff valve that's soldered to a copper water line. If you have galvanized steel or plastic supply lines, buy the appropriate shutoff valves for your system. Disconnect the faucet supply lines (Photo 1). If you have compression fittings, unscrew the compression nut and remove the old valve. If your fitting is soldered on, you can cut it off, but chances are there won't be enough pipe left to attach a new valve. Photo 2 shows how to unsolder an old fitting with a propane torch. Use a flame protecting cloth to keep flammable surfaces inside the cabinet from burning. Sand off remaining solder with an emery cloth, and then proceed to Photo 3 to hook up the new valve.