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An oxygen concentrator is a device that concentrates the oxygen from a gas supply (typically ambient air) by selectively removing nitrogen to supply an oxygen-enriched product gas stream. They are used industrially and as medical devices for oxygen therapy. Two methods in common use are pressure swing adsorption and membrane gas separation. Pressure swing adsorption (PSA) concentrators utilize multiple molecular sieves consisting of zeolite minerals that adsorbs pressurized nitrogen in fast cycles.