How to Install a Stop Valve for a New Dishwasher
No-sweat compression fittings make the job, well, no sweat
If you don't already have a dishwasher, then the existing hot-water supply line to the kitchen sink probably has a two-way stop valve with a single outlet to the faucet. To add a dishwasher, you'll need to replace it with a three-way valve, which has two outlets: one for the faucet (the riser) and one for the appliance. The easiest way to install the new valve is with compression fittings, which don't require soldering. Just follow these steps.
Remove the old valve. Turn off the hot-water supply to the sink and put a bucket beneath the old hot-water valve. Disconnect the riser from the faucet, then cut the supply pipe (called the stub-out) with a tubing cutter. Keep as close as possible to the existing valve. Tighten the cutter's knob slightly after every turn; the cut has to be square and the pipe undistorted for a compression fitting not to leak.
Fit the new valve. A compression fitting creates a seal when its nut squeezes a brass ferrule against the valve opening. Slip the compression nut and ferrule, in that order, over the cut pipe end. Push the new three-way valve onto the pipe and nest the ferrule flush against the valve's threads. Now slide the nut over the ferrule and, without jostling it out of position, hand-tighten until it's snug.
Make the new connections. To connect the dishwasher and the faucet to the new valve, cut and bend new tubing to fit the valve's two outlets
See steps for installing dishwasher Slip a nut and ferrule over the end of each tube, then hand-tighten the nuts to the valve. As you hold the valve steady with pliers, give all three compression nuts a quarter-turn with an adjustable wrench. Do not overtighten; the nut can distort the ferrule and cause a leak. Turn the water on and check for leaks. If you see any, turn the water off and give the leaking nut another quarter-turn before retesting.