Abstract: An installation for exchanging gas cylinders includes an enclosed space preferably with controlled access, at least a couple of stations, one for depositing an article to be exchanged and the other for collecting an article to be taken away, each station having a device for retaining the article that can be switched between an open configuration and a locked configuration, the retaining devices of the two stations being coupled such that the locking of one retaining device around an article to be deposited in the deposit station authorizes at least temporarily the opening of the retaining device of an article to be taken away for its removal.

Abstract: An arc welding process and apparatus utilising an electrode and a counter-electrode between which a column of plasma forms. A first unidirectional current source is located between the electrode and the counter-electrode, and a second unidirectional current source is located between the counter-electrode and the member to be welded. These two sources simultaneously pass the two unidirectional currents.