Why? sometimes it has a leak, or the pipes are loose, or even some times there is extra water in the fosset that drips out.
This depends what shut off valve is in question here. Where the leak is and what type of material is the shut off valve made of.
One of the supply lines has a hole or the faucet itself. You probably have seen the water by the time you get this. You probably have to shut the whole house off, most tubs don't have their own shut off valves.
An air-intake engine shut-off valve regulates air-flow to the motor, and operates as an emergency shut-off valve. There are also shut-off valves on water hoses, so shut-off valves really control the inflow of any liquid or gas.
As long as there are working valves to shut off the hose at the washing machine connection, you do not need to shut off the main. If there are no valves there or they do not work, you must shut off the main before starting and then take advantage of this time to install shutoff valves as well.
outside of the home
Tubs usually do not have shut off valve for them. You have to shut off the main supply. Depending on how the house is plumbed, you may be able to shut the cold supply to the water heater and that will shut off both the hot and cold or the main line where it comes into the house.
It doesn't need a shut off valve. In fact only Ford Motor Company installs fuel shut off valves in their cars.
Gate valves used to be, now they are being superseded by ball valves.
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