Can a Leaking Argon Gas Line Draw in Air and Create a Mixture?

[Bladestein]

I have an argon line used for atomization and backfilling a VIM melting chamber. If there is a leak on the argon line (at a fitting, valve, etc), will this leak actually draw in air when gas is turned on and flowing through pipe creating a mixture of argon and air?

 

[jerromyjon]

gas is turned on and flowing through pipe

Is the argon under pressure as in mig welding systems or is it drawn into the chamber by the vacuum?

 

[Bladestein]

Pressure line.

 

[jerromyjon]

If the pressure is considerably higher than atmospheric pressure I can't image it would draw in air, but according to the Bernoulli principle the higher velocity of the flow the lower the pressure that accompanies it, so the flow rate and the pressure have to be considered. Can we assume the air has been purged from the system initially?

 

[Bladestein]

If the pressure is considerably higher than atmospheric pressure I can't image it would draw in air, but according to the Bernoulli principle the higher velocity of the flow the lower the pressure that accompanies it, so the flow rate and the pressure have to be considered. Can we assume the air has been purged from the system initially?

Air has been purged from the system in theory. System pulls vacuum to remove air then back filled with argon. But when backfilling is air being pulled in also.

 

[jerromyjon]

But when backfilling is air being pulled in also.

Yes that would definitely drawn in air if there is a leak, and argon molecules are larger so they might not leak out when the system is pressurized.
Can you verify if the vacuum holds? That's how I detect leaks in air conditioning systems prior to filling them with freon.

 

[Bladestein]

We pull a vacuum to approximately 200mTorr and then leak check for 1 minute. We get leaks of 20-50 which in my opinion is no good. We helium check for leaks but even if we had a leak up of 20 the helium check finds no leaks. The end result is out of spec oxygen on our final product. We could be pulling air through leaks in chamber even when back filled with argon and/or the argon line that pumps argon into the chamber for backfill could have leaks that also pulls air into chamber

 

[jerromyjon]

I think I may be stumped as well for solutions, the only one I have left to think of is soap and water. Pressurize the system and get spraying...