Gas supply system with purge means

Claim 1

A gas supply system comprising: a supply conduit having an inlet and an outlet, and a downstream direction of flow from said inlet to said outlet; a delivery conduit; a vent conduit; a selector valve having a first port connected to said outlet, a second port connected to the delivery conduit, and a third port connected to the vent conduit, said selector valve being so constructed and arranged as selectively to interconnect said first and second ports in a first setting, said first and third ports in a second setting, and none of them in a third setting; a purge conduit having an inlet and a discharge port,said purge conduit entering said supply conduit, said discharge port being directed upstream in said supply conduit and discharging adjacent to the inlet of the supply conduit, said supply conduit inlet being adapted to receive a first gas from a valved source thereof, said purge conduit inlet being adapted to receive a second gas from a source thereof; and valve means in said purge line between its inlet and discharge port, whereby with the said selector valve in said second setting, said valve means can be opened to discharge second gas into said supply conduit to purge gases present in said supply conduit therefrom by sweeping action and discharge through the third port, and said valve means can then be closed and said selector valve be set in its third setting, and the source of first gas removed and replaced, and the selector valve can thereafter be returned to said second setting and said valve means opened for further purging with second gas, and thereafter said valve means can be closed to stop supply of second gas, and said selector valve can be set to said first setting to supply first gas to the delivery conduit.