while tig welding aluminum at work on our 250 syncrowave, lately i am getting a lot of bad cylinders of gas, 75/25- argon helium.
this is confirmed by me once i get a suspected bad cylinder, i hook up the previous, almost empty bottle, and everything runs fine.
when welding with the bad gas, i get a very erratic arc, both before and after adding filler, and it is very hard to achieve a nice appearing bead. the arc is so unstable you can actually hear the difference, and the etching / cleaning zone is like twice the size with the bad gas, compared to the good gas.

after switching out cylinder the past couple of weeks, our supplier, airgas, took one of the bottles i said was bad, had its contents analyzed, and sure enough it had nitrogen and oxygen in it. that made me happy knowing it was bad gas.

but, they said they checked 5-10 other cylinders, these checking out good, put them aside just for me, and yesterday i had 3 of them all act up just as before. again, hooking up the one cylinder that ran good for almost 4 days cured the problem.

i kind of dont want to believe they actually tested the other cylinders they are saying are good, since i wasnt there. i think they are just covering their selves.

i talked to an engineer at a place called nupure,, and he said he hears of this problem all the time. he said some traces of nitrogen is normal with argon and helium, but said there should be absolutely no traces of oxygen. they do make two different styles of gas purifiers, but they are very pricey at 2-3k....

just curious if you guys have had multiple bottles of bad argon, argon/helium in the past ? how many did you have in a row that were bad ? i searched the internet and found multiple stories of bad gas.

also, some time ago, someone told me to get a clean piece of steel, stike and arc at low amps, keep the torch there until the gas stops purging, and i think he said if it shows a dirty, discolored area in or around the solidified puddle, it means contaminated gas, if it looks all clean the gas is good.

can any of you confirm the above statement... im going off memory.

thanks guys for any input you can provide