Patent ID: 7015412

Claim:
An apparatus having a variable flow-control device incorporated as one element in a metal inert gas welding system that includes a shielding gas delivery hose transporting shielding gas from a shielding gas source to a mechanism incorporating a gas solenoid or similar off-on device and a welding torch having a shielding gas nozzle; wherein said apparatus comprises: a) said variable flow-control device is inserted in said shielding gas delivery hose which is greater than about 5 m (15 feet) in length creating two gas passages, one closest to said solenoid end and one closest to said shielding gas supply end, and b) said variable flow-control device controls the rate of flow of the shielding gas from said shielding gas source to said gas solenoid, and c) is of a design such that, when welding is stopped and thereby said solenoid blocks the flow of the shielding gas, said variable flow-control device allows the gas pressure in said gas passage closest to said solenoid end to essentially equalize with the higher gas pressure in said gas passage closest to said shielding gas supply end, and d) said variable flow-control device is located such that said gas passage at said solenoid end, when welding is stopped, contains a predetermined amount of the shielding gas, now stored at the higher pressure, that is sufficient to supply an extra amount of the shielding gas at the weld start to displace air that enters said welding torch and said shielding gas nozzle when welding is stopped in addition to supplying an extra amount of the shielding gas at the weld start to displace air in the weld start area.