Two Conditions, Two Valves There are two styles of compression valve commonly used in sink hookups. When the water pipe enters the sink cabinet through the back wall, a right-angle-stop valve is required to make the 90-degree turn to the faucet. When it enters through the floor, no turn is needed so a straight-stop valve is used. You must also consider the type of pipe that supplies water to the sink. If it's made of 1/2-in. rigid copper, you'll need a compression fitting to connect the valve. If the piping is threaded galvanized iron, use a valve that has female iron-pipe threads. Here, we'll show two different installations: adding an angle-stop valve to galvanized iron pipe and putting a straight-stop valve onto copper pipe. Note that angle- and straight-stop valves are available for both copper and iron piping.

Angle-Stop Valve Your first step is to shut off the water to the entire house at the meter. Drain the system by opening the sink and tub faucets on the lowest floor. Some water might remain in the system, so keep a small bucket handy. Next, use a wrench to loosen the water-supply tube from the adapter. Break the 3/8-in. compression nut free with the wrench, then twist it off with your fingers (step 1). To disconnect the other end of the supply tube from the faucet, use a basin wrench (step 2). The long handle of this wrench allows you to reach up behind the sink bowl and grab onto the faucet's coupling nut. With the water-supply tube removed, use a pipe wrench to grip the threaded galvanized pipe stub coming out of the wall. Then use an adjustable wrench to unthread the old adapter from the pipe stub (step 3). Take a wire brush and clean away hardened pipe dope from the pipe threads. Brush on a fresh coat of pipe-joint compound (step 4), then thread on the new valve (step 5). Tighten the valve using the adjustable wrench, but be sure to backhold the pipe stub with a pipe wrench. Lubricate the threads of the angle-stop valve with pipe-joint compound and attach the new flexible supply tube (step 6). Connect the opposite end of the tube to the faucet with the basin wrench.
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