Quote Originally Posted by GITONGA View Post
First of all remember you always install a filter driyer may it be a new install or a repair that involved exposing the unit to the atmosphere .then when you say sweep the unit with nitrogen it will depend on the task, did you have acid due to a burn out or you are trying to just get rid of foregn matter that might have entered the piping while installing that may be the little copper fragments you get when you debar the pipe or the black soot like stuff which you can avoid by running nitrogen through the system when you weld the piping i normally push though less than 5psi and that should keep your pipes clean after welding. then its a good practice to use the micron gauge and atripple vacuum .
Invest in a flow meter... 5 PSI is enough pressure to keep your filler metal from getting good penetration, there should be no pressure to speak of entering the piping, just volume to displace the oxygen.

For smallish pipe (under 1 1/2") I typically use 5 SCFH, if anything over that I will use 15 or even 20 SCFH, the trick is to get in, get it hot, weld it up and get out...

It's funny, but you would be amazed at the amount of newbie techs we get that use the "if it's glowing it's flowing attitude". This is so wrong it's silly.

I have literally brazed 7 to 10 time the amounts of joints with one bottle of oxygen and acetylene than most apprentices and they almost always have leaks, with lots of practice comes a proven technique.

Good luck

GT