How to Install a Water Shut-Off Valve

Locate your home's main water shut-off valve — typically near the water meter at the street-side wall of your basement, crawl space, or utility closet. Turn it fully clockwise (or lever to perpendicular) to shut off all water to the house. Then open the faucet nearest to your work area and let it run until it stops — this drains residual water and pressure from the pipes. Open the faucet on the lowest level of your home as well to help drain the system by gravity. Place a bucket and towels under the pipe you will be cutting, because some water will remain trapped in the line no matter how well you drain.

If you are replacing an old valve, use an adjustable wrench to unscrew the compression nut connecting the supply line to the valve outlet, then unscrew the compression nut connecting the valve to the pipe stub-out from the wall. If the old ferrule (brass compression ring) is stuck on the pipe, do not try to pry it off — you can cut the pipe just behind it with a tubing cutter to get a fresh section. If you are adding a valve where none exists, simply disconnect the supply line from the pipe stub-out. Have your bucket underneath to catch any remaining water that drains out.

If you need a fresh pipe end — either because the old ferrule is stuck or the pipe is damaged — use a mini tubing cutter to make a clean, square cut. Clamp the cutter onto the pipe where you want to cut, tighten the knob until the cutting wheel contacts the pipe, and rotate the cutter around the pipe. After each full rotation, tighten the knob a quarter turn and rotate again. Repeat until the cutter slices through. The key is patience — forcing the cutter bends the pipe and creates an oval end that will not seal properly. You need at least 1 inch of straight pipe extending from the wall to seat the compression fitting.

After cutting, the inside edge of the pipe will have a small raised burr that restricts water flow and can prevent the ferrule from seating. Use the triangular reamer blade on the back of your tubing cutter (or a separate deburring tool) to scrape away the inside burr by rotating it inside the pipe opening. Then wrap a strip of emery cloth around the outside of the pipe and sand the last inch until it is bright and shiny — this removes oxidation and ensures the compression ferrule makes full metal-to-metal contact for a watertight seal. Wipe the pipe clean with a dry rag to remove any grit or copper shavings.

Before attaching the valve, slide the compression nut onto the pipe first with the threaded end facing away from the wall. Then slide the brass compression ferrule (also called a compression ring or olive) onto the pipe behind the nut. The ferrule is the small brass ring that came with your valve — it sits between the nut and the valve body and gets crushed into a tight seal when you tighten the nut. Make sure both pieces slide freely on the pipe before proceeding. If the pipe has a slight bend that prevents them from sliding, gently straighten the pipe with your hands.

Push the valve body onto the pipe end until it seats firmly against the ferrule. Hold the valve with one hand to prevent it from spinning, then slide the compression nut up and thread it onto the valve body by hand — tighten it finger-tight first. Using an adjustable wrench, tighten the compression nut an additional one-half to three-quarters of a turn past finger-tight. This is enough to crush the ferrule into a seal without deforming it. Resist the urge to crank it down further — overtightening is the most common cause of compression fitting failure, as it cracks the ferrule or distorts the pipe and creates a leak that gets worse over time.

Attach your new braided stainless steel supply line to the valve's outlet port. Most quarter-turn valves have a 3/8-inch compression outlet — match your supply line fitting to this size. Thread the supply line's compression nut onto the valve outlet by hand, then tighten with an adjustable wrench — again, one-half to three-quarters turn past finger-tight. Connect the other end of the supply line to the fixture's inlet (faucet tailpiece or toilet fill valve) and hand-tighten, then snug with a wrench. Use Teflon tape on any threaded (non-compression) connections — wrap 3-4 turns clockwise around the male threads before connecting.