a pressure - swing adsorption device in accord with the invention may be constructed using only one adsorption vessel to purify a gaseous feed stream . an efficient implementation of this single bed system is illustrated in fig1 and although this description represents the preferred embodiment , additional variations and improvements are possible with respect to apparatus and configurations using this system . in fig1 an adsorbent bed , 1 consisting of a volume of adsorbent medium such as a molecular sieve adsorbent is connected at the opposite ends thereof 2 and 3 by a valve system including valves v1 , v2 , v3 , and v4 which operationally connect , according to a predetermined cycle , bed end 2 to source 4 which is capable of providing a higher pressure 6 and a lower pressure 5 with respect to a given &# 34 ; ambient &# 34 ; pressure level . the opposite end of bed 3 is connected by a check valve v5 and restriction valve v6 to a product tank / surge vessel 7 which provides the supply of product gas at a pressure regulated by valve v7 . the source of the gas or fluid to be purified is introduced to the system at inlet 9 . a product gas outlet is provided at 10 and a purge gas outlet is shown at 11 . in prior art single bed cycles , the compressor is not used effectively while the adsorption vessel is undergoing the regeneration step . however , in the use of an apparatus in accord with the cycle of the invention , the compressor is used to lower the vessel pressure during regeneration , thereby improving regeneration efficiency . in the preferred embodiment , purification of air to produce oxygen or oxygen - enriched air is one useful example of the cycle . during the adsorption phase of a cycle shown in fig2 a , a compressor pumps air from the atmosphere to an adsorption vessel , through valves v3 and v2 , while valves v1 and v4 are closed . the adsorption vessel is filled with a suitable adsorbent such as molecular sieve . in an oxygen concentration system the adsorbent will have a preferential affinity for nitrogen , and so removes it from the passing stream . the nitrogen depleted gas passes through a check valve , and also a parallel , partially restricted line , and enters the product tank . a flow of gas is drawn from this tank as the product supply of &# 34 ; purified &# 34 ; oxygen . when the adsorbent &# 39 ; s capacity for nitrogen is sufficiently exhausted , the position of all four valves is reversed and the system will be purged as the cycle is shown in fig2 b . nitrogen - enriched gas is drawn from the adsorption vessel through valves v1 and v4 while valves v3 and v2 are closed . since the compressor discharge is at atmospheric pressure , this creates a vacuum in the adsorption vessel . product enhanced purity fluid from the product tank is drawn through the restricted line , to purge the adsorbent . as the adsorption vessel pressure drops , the effect of this purge becomes more efficient . in this regard , proper design with respect to overall system pressure insures that the pressure in the product tank is sufficient to supply both product and purge flows . after sufficient purge has been provided to exhaust all nitrogen retained by the bed during the previous adsorption step , the sequence is repeated . flow patterns of the repetitive operating cycle of the invention is shown in fig2 a and 2b which respectively depict the process and purge states of the system . in a demonstration of the cycle of the apparatus , a compressor adsorbing system configured in accordance with fig1 was interconnected with a 10 pound enclosed bed of a densely packed molecular sieve adsorbent ( grade 13x ). at a pressure level of 2 . 8 p . s . i . g . provided by the compressor and a suction of - 2 . 4 p . s . i . g . during the purge stage , and using a product vessel enclosing a volume of approximately 6 liters , with ambient temperature air ( 25 ° c .) as the fluid source , the enhanced efficiency of the cycle of the invention was able to produce a consistently high purity ( 90 %) supply of oxygen at a rate in the range of approximately four to five liters per minute ( or , alternatively stated 95 % oxygen at the rate of 4 . 5 liters per minute ). the utilization of such an enhanced cycle in treatment apparatus for chronic obstructive pulmonary disease or for other therapeutic purposes to an individual patient provides the therapeutic benefit of the essentially continuous delivery of a high purity oxygen in a level consistent with anticipated physicological demands of an individual patient in an apparatus having a simplified mechanical configuration .