Opening bottles for mig shielding gas

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It's all new to me.............. but I thought that mig shielding gasses were high pressure and the bottle valves needed to be opened all the way, but recently I had someone who welds alot at work tell me that I only needed to open it enough to get enough gas flow for my needs.what's the scoop ?VEC
Reply:hey i dont think that the shielding gasses are double seating valves like an O2 cylinder...so you dont have to open them all of the way... i may be wrong but that is what i think....
Reply:Hooks:You are right in your thinking,  welding gasses  are high pressure --2000 PSI plus --and should be opened all the way to back seat the valve. I always open the valve on all tanks --other than flamable gasses-- all the way.  I am not real sure about CO2  I know it is not quite as high pressure as the argon  and argon mix gasses but I still open it all the way as a habit.  The  guy that told you that the valve does not have to be back seated probably is not the one who is paying for the gas  so why does he really care if there is leakage around the valve stem. If you are the one paying for the gas you already know that the gas is rather expensive. so why let even a bit escape.J.W.
Reply:J.W. has it pretty well covered. Safe and nonvolatile gasses generally have a pretty good seal, yes. That's because no-one wants or needs a ton of blow while you are opening the valve but they are designed for back seating as the means of leakage prevention. I don't doubt that modern methods and materials have minimized leakage during the transition positions but I wouldn't want to relay on that as a given. Volatile and dangerous gas valves are designed to NOT leak no matter what position for obvious reasons. In fact it's best to only open as much as necessary to meet the flow needs. That's to povide a crude secondary safety factor. In case of reg fail the valve would be opened no more than a minimal amount.
Reply:Just one more thought on this subject:The valve on a high pressure tank -- whether it be welding gas or cutting oxygen--should always be opened slowly so the regulator and pressure gague can adjust to the high pressure  rather than be slammed with  2000 PSI in a sudden charge.  Never stand in front of the regulator  when opening the valve. It has never happened to me but I have seen pictures of regulators and gagues that have exploded because of this.Of course never use any type of oil on the threads of the regulator to tank connecting nut, or any part of the regulator for that matter.   Oil or grease is a fuel  when in a confined space with the high pressure gas or oxygen. Fuel and high compression =  combustion and or explosion -- which could be very hazardous to your well being.I have also seen pictures of this happening and it was not a pertty sight.       ! ! ! ! !  SAFETY FIRST  ! ! ! ! J.W.
Reply:J.W. , that about covers it. I agree completely.
Reply:I defintly open my CO2/ARGON tank all the way.  I never knew about the back seating until I was watching a welding video.  I now know why my gas use to go so quick.  Now it last quite a bit longer.