On May 11, 10:28*am, Pilgrim wrote:
What do I need to know and what precautions do i need to take to sweat
solder a 1/4 turn ball valve in 3/4" Cu pipe? The ball turns in a
plastic seat that looks like teflon.

Close the valve (or open fully) before applying heat; a half
open valve can dent the seal.
Don't heat the pipe first; most of the heat has to go to the
heavy part (the valve) not the pipe. The valve has to be hot
or the solder won't wick in.

My preference is to make both valve joints on a single heat.
You might want to dismount the handle, so it doesn't block your
flame or scorch.