In-line shut-off valves allow you to cut the water supply to individual fixtures or appliances and isolate a portion of the water supply system. Shut-off valves make the entire piping system more user-friendly and reduce the amount of time required to perform repairs. In-line shut-off valves may be installed during the rough plumbing phase of new construction or retrofitted at any time thereafter.
Mark the location of your cuts on the water supply pipe with a pencil or marker. Use a tape measure to determine the space required by the in-line shut-off valve and coupling.
Shut off the water supply to the pipe that will receive the new shut-off valve. Drain water from the supply system's pipes by opening plumbing fixtures, such as kitchen and bathroom faucets. Allow the water to drain from the pipes until the flow slows to a drip.
Attach a pipe cutter to the pipe. Tighten the pipe cutter's blade against the pipe's wall at one of the marks. Twist the pipe cutter around the pipe, occasionally tightening, until the cutter's blade slices through the pipe's wall. Hold a rag around the pipe or a bucket beneath the pipe to catch any remaining water. Attach the pipe cutter to the opposite mark and cut to sever the portion of pipe from the water supply line.
Measure and mark the length of the replacement pipe with a tape measure and pencil or marker. The replacement pipe must accommodate the in-line shut-off valve and coupling; allow adequate space for both fittings. Cut the replacement pipe with the pipe cutter.
Clean the interior of all fittings and the exterior of all pipes with emery cloth and pipe brushes. Abrade the fittings' and pipes' metal surfaces until they shine.
Apply flux to the outside of pipes and the inside of fittings with a flux brush. Coat the fittings and pipes with a thorough, continuous layer of flux.
Assemble the replacement pipe, coupling and in-line shut-off valve. Place the assembly onto the water supply line. Attach a fire-retardant cloth to combustible surfaces surrounding the work area, if necessary.
Heat the joints with a propane torch. Apply the flame evenly along a joint, occasionally pressing the tip of wire solder against the joint. Direct the torch's flame primarily over the fitting, not the pipe. When solder melts upon contact with the metal, remove the flame from the joint and press the solder into the joint until a ring of molten solder squeezes from the joint's seam. Press a wet rag onto the joint to cool the joint and wipe away excess solder.
Apply heat and solder to each joint. Allow the newly soldered joints to cool before turning on the water supply.
Allow pipes to fully drain before soldering; a water-filled drain prevents pipes from fully heating and solder from evenly filling a joint. If you have trouble sweat-soldering, consider purchasing an electronic soldering tool.
Always protect adjacent surfaces from the torch's flame.