If this happens to you you can simply replace the valve with a new valve that matches the old one.
Replace water shut off valve under bathroom sink.
Then open a faucet on the lowest level of your house and another faucet on an upper level to drain the pipes.
The water to a kitchen or bathroom sink is supplied through small copper or flexible neoprene tubes from a small control valve called a stop or shut off valve under the sink.
Under sink shutoff valves also called fixture shutoffs or stop valves allow you to turn off the water to the sink or other fixture without having to use the home s main shutoff.
These inexpensive little valves rarely get used and when they do sometimes they leak.
If you have a gas water heater turn the knob to the pilot position.
There are two basic types straight stops and angle stops and these valves normally remain on and are seldom closed functioning maintenance free for years.
When cutting the supply line cut slowly and gently so.
Shut off the water at the main shutoff valve.
Cut the supply line with a pipe cutter leaving enough room between the escutcheon plate and the cut to allow installation of the valve fitting.
Deburr the pipe with a deburring tool.
Open the faucet to drain the line.
Prepare for valve replacement.