Back purging

[Error404]

OK so I'm getting ready to weld up my downpipe and exhaust - I've not back purged before so just wanted to see how my plan sounded. Maybe anyone who's done this before can offer some tips?

Here is what I'm planning to do:

I've bought a Y-piece splitter, a second flow meter and a length of air hose.





Argon is denser than "air" so it should sink to the bottom of the exhaust tube. So I plan to bolt a plate to the turbo flange of the downpipe to seal the end, and make some kind of bung to poke the gas hose through at the top. Then tape up all the joints except the very top one, to give the air somewhere to get out. Then gently fill with gas.
Rough calc for the volume of a 1m length of 3" tube ~ 4.5L. So I can purge the air out for maybe a couple of minutes at say 4Lpm and then turn the flow down to say 1Lpm to maintain positive pressure in the tube while I weld.

Does that sound like a plan?

[terrybullwon]

Tin foil, plasticene and foil tape to seal it up?

[AndyP]

Try searching on the welding forums, you can make a plug that will just isolate the area you are welding rather than filling the whole exhaust with gas. If I find the pics, I'll post them up.

[AndyP]

I'm thinking a home made version of this:-

http://www.pipe-ltd.com/Portals/0/Images/PIPE%20products/Pipe%20Purging/Purging%202012/Double%20Seal.pdf

[Error404]

Yeah I thought about using a ball bladder or something like that but I have enough to do at the minute, so I might just throw some money at some Argon

[SteveH]

I just poke the purging tube into the pipe and block each end with a clean rag. Providing you purge the O2 out and don't have the argon pressure too high you can't go wrong. Even without back purging a Tig weld will be plenty strong enough. Gas flow would only be affected in a pipe if the tube was narrow diameter, had loads of joints and non of them were purged.