I need to finally setup a backpurging setup at my shop here. In the past I have used a smaller tank of argon seperate from my main tank for purging. Right now I use an M125 tank exclusively. I have it on my Sync 500 normally, and on the occasions that I need to use my little 110 MIG I just switch the line over to that and roll it out. I'm debating between getting a new regulator and making a T setup like Weir's thread, or getting a smaller Q60 tank for the MIG and for purging. I also kind of need a new reg anyway, the one I have is crappy and sometimes leaks a little. So my options are get another regulator, probably one with 2 meters on it, and T off my 125 tank, or get another tank and a new reg for the 125, put the old regulator on the new tank and leave it on the MIG and also use it for purging. The new tank will cost me right around $200 for the bottle and the fill, plus another regulator, so it's obviously gonna cost more, but are the benefits worth it? FWIW I very rarely use the MIG since I suck at MIG welding and I'd rather just TIG all my work, so having its own bottle would be a nice side benefit, but I'm more concerned with whether it's better to purge off a seperate bottle.

 

I run a twin reg on 1 bottle. Can't see any downside to doing it this way other than if you wanted a MASSIVE amount of flow, the reg does get very cold when running for a while with the purge on, and obviously you use more.

In the UK we pay rentle per bottle, so it would cost more, plus take up more space etc, but if you have to go and get refills yourself then i suppose you make less trips.