Oxygen-enriched air

A process for producing oxygen-enriched air for respiration which comprises the sequential steps of passing air under superatmospheric pressure in a first direction into an inlet end of a unitary bed of an adsorbent that preferentially adsorbs at least moisture and nitrogen, and collecting an oxygen-enriched product gas from an outlet end of the bed in a reservoir at superatmospheric pressure, passing oxygen-enriched product gas from the reservoir through a pressure regulator to reduce the product gas pressure to a predetermined value for delivery for end use, regenerating the bed by venting the bed to atmospheric pressure in a direction counter-current to that of the superatmospheric pressurized air introduction in the first direction, evacuating the bed in the said counter-current direction to below atmospheric pressure, regulating the venting and the evacuating of the bed by utilization of selected differential pressures so that at the inlet end of the bed the actual volume of gas withdrawn during the venting and the evacuating exceeds the actual volume of superatmospheric pressure air fed into the inlet end of the bed in the first direction, backfilling the bed in said counter-current direction to generally atmospheric pressure by introducing product-quality gas from a source at superatmospheric pressure, whereby the regeneration of the bed is enhanced by moving residual gaseous material in the bed closer to the inlet end of the bed to thereby enhance desorption of adsorbent at the outlet end of the bed.