Abstract: An invention is provided which contains a pressure isolation chamber coupled to a shielding gas system such that some of the shielding gas is directed to the isolation chamber and as the pressure in the shielding gas system decreases the pressure within the chamber decreases. The chamber is coupled to a pressure sensor or switch, which senses the pressure in the pressure isolation chamber. The pressure isolation chamber is blocked by a normally-closed valve such that if the system pressure increases, the pressure within the pressure isolation chamber does not increase accordingly, until the normally-closed valve is opened to allow the pressure in the pressure isolation chamber to equalize with the system pressure. The pressure switch is coupled to a control system such that when the pressure senses that the pressure in the pressure isolation chamber drops below a threshold the control system and/or the pressure switch ceases the welding operation so that a defective weld can not be created.