In a process for supplying a pressurized gas, a pressurized gas at a high production pressure is produced as an end product by separating a gaseous mixture in a separator apparatus (3, 5), a liquid to be pressurized is stored in a store (9), storing liquid is tapped, and it is pressurized with a pump (11) and at least part of the pressurized liquid is sprayed in a sprayer (27) to produce the pressurized backup gas (29) having substantially the same pressure or a pressure higher than the pressurized gas to be produced, liquid is circulated in a substantially vertical duct (13), optionally within the cold box (33) of the separator apparatus, and at least part of the duct length is at a level above the sprayer and before and/or after starting up the pump (11), liquid is sent from the duct to the sprayer where the liquid is sprayed to provide pressurized backup gas having substantially the same purity or a purity higher than the pressurized gas to be produced (31).
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