I worked overseas years ago and I swore we used Co2 for shield but maybe I was dreaming. I did try the allen screw trick and nothing changed, gas still blows out the relief valve. I backed the screw completely out and ran it back in. No change. I backed it out and stuck a utensil up to touch what the allen screw rests against expecting some resistance but no, it's loose. So I guess they are shop bound. I still don't understand why this happened in the first place.