Re: back purging???
 

That's SolarFlux. It sucks ass. I wouldn't use it for anything but drain piping or bullshit like that.

When purging, you don't want to hold your torch in the pipe and blow argon in it. You want to have a splitter on your argon hose, or another bottle. Tape up all openings on the pipe. Punch a hole in one end and put an argon hose in it. Punch an equal sized hole in the other end. Allow argon to flow through until the exiting hole flow will put out a lighter flame, maybe give it a few more minutes, just to be sure. Then weld the joint you need to weld, removing the tape from it as you weld, not all at once. Otherwise, all the argon will flow out the bottom and you will lose purge.