Air leak in TIG sheilding gas. Faulty Gas Solenoid Valve?

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Hi, new guy here. My 1st post and already I'm asking for help Could a faulty Gas Solenoid Valve flow argon, but also allow air to enter the flow through the venturi effect?  Is there any explanation for a blackened electrode other than air in the flow?  Will air in the shielding flow cause the arc to be weak and “thready”I think I'm suddenly getting a lot of air in my argon flow.  By suddenly I mean one minute everything was fine and the next minute all I'm getting is sputtering, a weak arc, a sort of corona between the tip and the work and an electrode blackened all the way up to the collet.  Plenty of gas flow is coming out of the cup but I don't think it's all argon anymore. (The gas lens screen is also melted. But I haven't had it off for years, so it may have been that way for a while.)I was TIG welding some 0.065” wall rectangular steel tubing.  I laid down an inch of bead just fine. Then I skipped forward an inch and tried to start another bead.  Nothing had been changed.I've tried different cups and electrodes, no change.  The work is well grounded L-Tec  Heliarc 250 HF Plus  about 20 years oldHeliarc HW-17 gas cooled torchFoot pedal controlFor it's age, the machine has few hours on it.  I'm just a hobby welder (mostly light stuff like bicycle frames) and have used it very little in the last few years.  The original owner was also a bike frame builder.  Framebuilding, whether O/A or TIG, is hours of prep for minutes of torch time.The problem seems similar to what happened when I tried to weld after having to disconnect the hose from my flowmeter to the welder last year.  It didn't occur to me I'd have to purge air from the hose before welding again.  This is much worse than when I had a bad O-ring in the torch cap.There is no leak between the flowmeter & the GSV. It takes a week for pressure in the gauge to go down.  When I blow into a new cup there doesn't seem to be any leak between the torch and GSV. I used soapy water to check for bubbles.The welder is in my basement & I had to hire piano movers to get it there.  So bringing the machine in for service isn't Plan A.
Reply:Is your collet crushed?Weld like a "WELDOR", not a wel-"DERR" MillerDynasty700DX,Dynasty350DX4ea,Dynasty200DX,Li  ncolnSW200-2ea.,MillerMatic350P,MillerMatic200w/spoolgun,MKCobraMig260,Lincoln SP-170T,PlasmaCam/Hypertherm1250,HFProTig2ea,MigMax1ea.
Reply:did you change out the melted gas lens?
Reply:Hmmmmm without seeing what you ended up with I can only guess.....Black or dark tungsten after the weld means too short of POST flow or none at all......A weak arc could be several things does it have a good High Freq?    check your ground connections........  Miller Dynasty 350Twenty Six HammersThree Crow BarsBig Rock
Reply:Is your collet crushed?
Reply:Originally Posted by BikesmithCollet looks great.  But I have to ask, what would a damaged collet suggest as a cause for my problem?.