A leak in your kitchen sink valve is a problem that needs to be taken care of immediately. It will be spraying water all around the undersink cabinet. Thankfully, it’s not an especially difficult to fix the sink valve, also known as the shut-off valve. It only takes a few tools that you probably have in the house anyway.
Step 1 - Preparation
The very first thing to do is to wrap each of the jaws of the slip joint pliers in masking tape. This will afford you a better grip while preventing scratches on the kitchen sink valve.
Step 2 - Packing Nut
There’s a simple repair on the kitchen sink valve that you can attempt. Behind the handle on the valve you’ll find a packing nut. Use the pliers to grab it and turn it very slightly—no more than 1/8 of a full turn in a clockwise direction. Sometimes this will stop the water flowing from the valve. If it works, fine. If not, you need to take more drastic steps.
Step 3 - Accessing the Washers
If tightening the packing nut hasn’t worked, the problem is almost certainly in the washer. To reach that you’ll need to take the sink valve apart. Start by turning off the water at the mains. Run the faucet so that the pipes can drain. You will need to have a small container of some kind handy for any water that’s retained in the valve itself.
Now you need to take the valve apart. This is something you can accomplish without removing the sink valve from the water line. Start by taking out the screw in the handle of the sink valve. Remove the handle, then use the pliers to take off the packing nut. From there you’ll be able to pull out the valve stem, which is threaded. The valve stem will have neoprene washers. Note where they are on the stem.
Step 4 - Washers
You’ll need to clean the washers. The leak might well be due to mineral deposits on them. Remove the washers from the valve stem and clean them with a rag. You’ll probably have to slowly work and bend them in order to make them flexible again and remove all the deposits.
Step 5 - Reassembly
Put the washers back on the stem, ensuring they’re in the proper places. Put the valve stem back in the sink valve and then tighten the packing nut to hold it in place. Don’t overtighten; if necessary you can tighten it more later. Put the handle back on and screw it into place.
Turn on the water at the mains and then open up the kitchen sink valve. Watch for any sign of a leak. If there’s a small one, tighten the packing nut a little, turning it clockwise with the pliers. This should eliminate all the leaks from the sink valve.