I tried to so some TIG welding for the for the first time this year and was trying out a new cylinder of SGS Argon gas. in the past Ive normally used a gas lens with a 4L cup on a WP9 torch and 1.6mm electrode, but I thought I'd try a no. 8 cup as it would be better for stainless rather than mild steel. So I tried this setup and was having big issues with porosity with the weld pool bubbling away and the electrodes being oxidised, with airlow I was running between 5 and 10LPM
My first thoughts that it was that it was possibly a bottle of dodgy Argon and then I tried another bottle (Adams gas) and it was the same, so Im beginning to wonder what was causing the issue, so in desperation I changed back to the 4L cup and that worked fine, so it didnt make any sense why changing the cup could make such a difference. anyway looking at the original gas lens it was a bit dirty
so a change to a new one made all the difference with the larger (size 8) gas lens, but the dirty gas lens still worked fine with the 4L cup.
glad I got my head around that problem
and glad I didnt go back to the supplier accusing them of supplying dodgy gas 
My first thoughts that it was that it was possibly a bottle of dodgy Argon and then I tried another bottle (Adams gas) and it was the same, so Im beginning to wonder what was causing the issue, so in desperation I changed back to the 4L cup and that worked fine, so it didnt make any sense why changing the cup could make such a difference. anyway looking at the original gas lens it was a bit dirty
so a change to a new one made all the difference with the larger (size 8) gas lens, but the dirty gas lens still worked fine with the 4L cup.glad I got my head around that problem
and glad I didnt go back to the supplier accusing them of supplying dodgy gas 