Sweat shut off valves are used in plumbing systems to be able to control the water supply lines in zones or sections.
Be sure to have the valve in the open position when you are soldering the valve on to the pipes.
If you solder the valve to the pipes with the valve in the closed position it occasionally solders the valve shut and you will not be able to open the valve.
Before the steps below make sure you drain all the water out of the water lines, any water in the pipe will not let the pipe get hot enough for the solder to take to the pipe or will cause a leak.
Important!!! Both the pipe and the fittings must be completly dry before soildering also make sure the valve is in the open position.