Shutoff valves let you turn on and off the water near your fixtures so you don’t have to shut off the water to the entire house to make repairs. They attach in different ways: by soldering, threading, or compression fittings. Compression fittings are the easiest to install and don’t require pipe dope, or compound. A metal sleeve makes the fitting watertight, as long as you install it right. Make sure you turn the water off before you start working. You will need to open the faucet you are working on and another one somewhere below it in the house so you can drain all the water out of  it.

Step1: DISCONNECT THE SUPPLY PIPE

Before you start, turn off the main water supply to the house. Unscrew the supply pipe at the wall. You will need to cut it with a mini-pipe tubing cutter or a mini-hacksaw if it is solder ti the wall. Make sure you are careful when cutting the tube. If it is out of round, the compression fitting will leak. Leave enough room between the escutcheon plate and the cut to install the fitting. Deburr the pipe with an emery cloth. Now slide the compression nut over the supply pipe as far back as you can.

Step2: PLACE THE COMPRESSION RING OVER THE END OF THE SUPPLY PIPE

The end should completely cover the end of the supply pipe. Thread the compression valve into the compression nut. The valve should slide snugly over the ring. Hand tighten the nut. If it doesn’t turn easily, add a tiny drop of oil to the threads. Don’t use pipe compound; the fitting doesn’t require it, and it can make the fitting leak.

Step3: TIGHTEN THE COMPRESSION VALVE TO THE NUT BUT DON’T OVER TIGHTEN IT

You will need one wrench to hold the back of the valve and keep it square and another to turn the nut. Follow the same procedure you used to install the valve to attach the supply lines. Only turn the water on for a second and let it flow into a bucket to flush the lines before installing the fixtures.