TIG back purge

For those of you TIG welding tubing with an back purge: How do you set
up the purge gas flow? Do you use a dual flowmeter, with one line going
to the TIG torch and the other feeding the purge? Or do you run the
purge from a "Y" off the main feed to the torch (with the "Y" hooked up
after the gas flow solenoid)?
The former method has the advantage of being able to regulate the CFH
of the torch and purge feeds separately. However, if you forget to shut
off the purge when you're done welding, you'll use up a tank of gas
pretty quickly. Or is this something you don't forget after you've done
it once or twice!
The latter set up forces the purge feed to run at the same CFH as the
torch, but the purge will stop and start automatically with the torch
feed.
Suggestions welcome - thanks.
Reply to
Tony Rentschler
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Actually, it doesn't. There's no way for you to know what the CFH is to the torch if you're allowing an indeterminate part of the flow to leak off elsewhere. Why do you think the flow would divide evenly if you have no mechanism to insure that it does? The only way that it could is if the back pressures of the torch and of the purge volume are identical. The odds of that being true are slight.
The other flaw in your scheme is that it lets air leak back into the purge area if you stop welding for a few moments. Often, the purge volume is large enough to need flow for some minutes before all the oxygen is purged from the area and you can start to weld. Then you can reduce the flow to just enough to overcome leakage from the purged volume after the oxygen has initially been purged. You rarely want the same flow rate for the back purge as you want for the torch, and you almost never want it to stop and start at the same time.
Gary
Reply to
Gary Coffman
What I have now is 2 flowgauge tubes on one regulator. That way I get accurate flow settings for the torch and the purge. You can buy twin head flow gauges. All the regulator makers make a version.
I just added a second flow tube to an existing one I already had.
I use a 1/4" acrylic hose to feed the gas from the flow guage to a small manifold of brass needle valves. 1/4" hose feeds from this little manifold to any purging gear I am using. That way I can turn the gas on and off very easily and quickly, even if I am running multiple purge jets.
I use push-on connectors for the hose, so I can assemble the purge gear quickly.
I have just started collecting purge gear, and building lots of custom purge baffles. It is a never ending quest.
Reply to
Ernie Leimkuhler

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