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An oxygen concentrator having molecular sieve beds for selectively adsorbing nitrogen from atmospheric air for increasing the oxygen concentration of a product gas, a reservoir for receiving the product gas, a compressor for charging atmospheric air to the sieve beds and a valve and valve switching

An oxygen concentrator having molecular sieve beds for selectively adsorbing nitrogen from atmospheric air for increasing the oxygen concentration of a product gas, a reservoir for receiving the product gas, a compressor for charging atmospheric air to the sieve beds and a valve and valve switching means for directing atmospheric air from the compressor to alternate sieve beds includes means for sensing the withdrawal rate of product gas from the reservoir and a microprocessor provided with the minimum time required for charging the respective sieve beds to achieve a product gas having a selected oxygen concentration at the sensed rate of withdrawal and means for switching the valve to charge the beds for the minimum charge time.

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1. In an oxygen concentrator comprising a plurality of molecular sieve beds for alternately receiving atmospheric air and for selectively adsorbing nitrogen therefrom to increase the oxygen concentration of a product gas recovered therefrom, a reservoir for receiving said product gas from said sieve

1. In an oxygen concentrator comprising a plurality of molecular sieve beds for alternately receiving atmospheric air and for selectively adsorbing nitrogen therefrom to increase the oxygen concentration of a product gas recovered therefrom, a reservoir for receiving said product gas from said sieve beds, a compressor and a valve cooperating therewith for charging said sieve beds with atmospheric air, valve switching means for alternately charging said sieve beds, and means for withdrawing said product gas from said reservoir, the improvement comprising: timing means for switching said valve according to a timing cycle, means for sensing the rate of withdrawal of product gas from said reservoir, and a microprocessor having memory means provided with the minimum time required for charging said sieve beds to produce product gas of a selected oxygen concentration at the sensed rate of product gas withdrawal from said reservoir, and means for adjusting the timing cycle for switching said valve to charge said sieve beds for said minimum time. 2. The oxygen concentrator of claim 1 wherein said means for sensing the withdrawal rate of product gas comprises pressure sensing means for sensing gas pressure in said reservoir. 3. The oxygen concentrator of claim 2 wherein said pressure sensing means comprises a transducer in said reservoir. 4. The oxygen concentrator of claim 2 wherein said microprocessor includes means for determining rate of flow of product gas from said reservoir in response to pressure sensings therein. 5. The oxygen concentrator of claim 1 including a surge tank communicating with said compressor for receiving atmospheric air therefrom between the time of alternately charging said sieve beds. 6. The oxygen concentrator of claim 1 including an oxygen sensor for sensing the oxygen concentration of said product gas withdrawn from said reservoir, said microprocessor including memory means provided with minimum selected product gas oxygen concentrations at different product gas withdrawal rates, respectively, means for comparing the sensed product gas oxygen concentration with the minimum selected concentration at the sensed withdrawal rate, and means for adjusting the timing cycle for switching said valve to increase the charging time of said sieve beds to produce a product gas having at least said minimum selected oxygen concentration at the sensed withdrawal rate. 7. The oxygen concentrator of claim 6 wherein said microprocessor includes said timing means. 8. The oxygen concentrator of claim 6 wherein said means for sensing the withdrawal rate of product gas comprises pressure sensing means for sensing gas pressure in said reservoir. 9. The oxygen concentrator of claim 8 wherein said microprocessor includes means for determining rate of flow of product gas from said reservoir in response to pressure sensings therein. 10. The oxygen concentrator of claim 6 including a surge tank communicating with said compressor for receiving atmospheric air therefrom between the time of alternately charging said sieve beds. 11. The oxygen concentrator of claim 6 including means for terminating operation of the apparatus if the minimum selected product gas oxygen concentration is not achieved within a selected period of time. 12. An oxygen concentrator for producing a gaseous product having an increased oxygen concentration from atmospheric air comprising: a plurality of molecular sieve beds, a compressor for charging atmospheric air into said sieve beds, a reservoir for receiving said gaseous product from said sieve beds, a surge tank for receiving atmospheric air from said compressor, a valve for directing atmospheric air from said compressor to said sieve beds and said surge tank and switchable between a plurality of different positions for charging different ones of said sieve beds, means for withdrawing said gaseous product from said reservoir, means for sensing the gas pressure in said reservoir, timing means cooperating with said valve for switching said valve between said different positions according to a timing cycle, and a microprocessor having means for determining the rate of flow of gaseous product from said reservoir in response to pressure sensings therein, memory means provided with the minimum time required for charging said sieve beds to produce gaseous product having a selected oxygen concentration at the determined flow rate from said reservoir, and means for adjusting the timing cycle for switching said valve to charge said sieve beds for said minimum time. 13. An oxygen concentrator for producing a gaseous product having increased oxygen concentration from atmospheric air comprising: first and second molecular sieve beds for adsorbing nitrogen from said atmospheric air to produce a product gas having a high oxygen concentration, a compressor for charging atmospheric air into said sieve beds, a reservoir for receiving said product gas from said sieve beds, a surge tank for receiving atmospheric air from said compressor and for charging said sieve beds therewith, a valve having a first position in which atmospheric air is charged into said first sieve bed from said compressor and said surge tank and simultaneously adsorbed nitrogen is vented from said second sieve bed, a second position in which atmospheric air is charged into said second sieve bed from said compressor and said surge tank and simultaneously adsorbed nitrogen is vented from said first sieve bed, and an intermediate position between said first and second positions in which atmospheric air is charged into said surge tank from said compressor, means for withdrawing said product gas from said reservoir, means for sensing the rate of withdrawal of product gas from said reservoir, switching means for switching said valve between said first and second positions, and microprocessor means cooperating with the product gas withdrawal sensing means and said switching means having memory means provided with the minimum time required for charging said sieve beds to produce product gas of a selected oxygen concentration at the sensed rate said gas is withdrawn from said reservoir, and for switching said valve to said first and second positions for said minimum charging times. 14. In a process for selectively increasing the oxygen concentration of a gaseous mixture comprising switching a valve between a first position to charge atmospheric air under pressure from a compressor into a molecular sieve bed and selectively adsorbing nitrogen therefrom to produce an oxygen enriched gaseous product and a second position in which desorbed nitrogen is released from said sieve bed, directing said gaseous product from said sieve bed to a reservoir, and withdrawing portions of said product from said reservoir, the improvment comprising: intermittently sensing the pressure of said gaseous product in said reservoir, comparing the intermittent pressures sensed and determining the flow rate of gaseous product withdrawn from said reservoir, adjusting the timing cycle for switching said valve to charge said sieve bed for a minimum time necessary to produce product gas of a selected oxygen concentration at the determined flow rate, and switching said valve according to said adjusted timing cycle. 15. In a process for selectively increasing the oxygen concentration of a gaseous mixture containing oxygen and nitrogen wherein a compressor alternately charges said gaseous mixture under pressure to a first and a second sieve bed, said sieve beds adsorbing nitrogen from said gaseous mixture to produce an oxygen enriched gaseous product and wherein said sieve beds are alternately charged by directing said gaseous mixture to a switching valve having a first valve position in which said compressor charges said first sieve bed and a second position in which said compressor charges said second sieve bed, and directing said gaseous product from said sieve beds to a reservoir, the improvement comprising, (a) providing a timing cycle for switching said valve to said first and second positions, (b) periodically sensing the pressure of said gaseous product in said reservoir and calculating therefrom the rate of flow of gaseous product withdrawn from said reservoir, (c) determining the minimum time required to charge each of said first and second sieve beds to produce a gaseous product having a selected oxygen concentration at the rate of flow said gaseous product is withdrawn from said reservoir, (d) adjusting the timing cycle for switching said valve for charging said sieve beds at said minimum required time, and (e) switching said valve between said first and second positions according to the adjusted timing cycle, whereby said compressor alternately charges each of said sieve beds for said minimum required time. 16. The process of claim 15 including providing a surge tank communicating with said compressor, said surge tank being charged with atmospheric air from said compressor when said valve is intermediate said first and second positions, and wherein pressurized gas from said surge tank assists in alternately charging said sieve beds when said valve is in said first and second positions, the improvement comprising providing a timing cycle for switching said valve to said first and second positions, and switching said valve according to the adjusted timing cycle. 17. In an oxygen concentrator comprising a plurality of molecular sieve beds for alternately receiving atmospheric air and for selectively adsorbing nitrogen therefrom to increase the oxygen concentration of a product gas recovered therefrom, a reservoir for receiving said product gas from said sieve beds, a compressor and valve cooperating therewith for pressurizing said sieve beds with atmospheric air, valve switching means for alternately charging said sieve beds, and means for withdrawing said product gas from said reservoir, the improvement comprising: (a) an oxygen sensor for sensing the oxygen concentration of product gas, (b) means for sensing the rate of withdrawal of product gas from said reservoir, and (c) a microprocessor having (1) memory means provided with the minimum time required for charging said sieve beds to produce product gas of a selected oxygen concentration at the sensed rate of withdrawal from said reservoir, (2) memory means provided with minimum selected product gas oxygen concentration limits at different withdrawal rates from said reservoir, respectively, (3) means for switching said valve for charging said sieve beds for the minimum time required to produce product gas having said selected oxygen concentration at the sensed rate of withdrawal, (4) means for comparing the product gas oxygen concentration sensed by said oxygen sensor with the minimum selected product gas oxygen concentration at the sensed withdrawal rate, and (5) means for increasing the time for charging said sieve beds to produce product gas having at least the minimum selected oxygen concentration at the sensed withdrawal rate. 18. The oxygen concentrator of claim 17 including a surge tank communicating with said compressor for receiving atmospheric air therefrom between the time of alternately charging said sieve beds. 19. An oxygen concentrator for producing a gaseous product having increased oxygen concentration from atmospheric air comprising: first and second molecular sieve beds for adsorbing nitrogen from said atmospheric air to produce a product gas having a high oxygen concentration, a compressor for charging atmospheric air into said sieve beds, a reservoir for receiving said product gas from said sieve beds, a surge tank for receiving atmospheric air from said compressor and for charging said sieve beds therewith, a valve having a first position in which atmospheric air is charged into said first sieve bed from said compressor and said surge tank and simultaneously adsorbed nitorgen is vented form said second sieve bed, a second position in which atmospheric air is charged into said second sieve bed from said compressor and said surge tank and simultaneously adsorbed nitrogen is vented from said first sieve bed, and an intermediate position between said first and second positions in which atmospheric air is charged into said surge tank from said compressor, means for withdrawing said product gas from said reservoir, means for sensing the rate of withdrawal of product gas from said reservoir, an oxygen sensor for sensing the oxygen concentration of said product gas withdrawn from said reservoir, switching means for switching said valve between said first and second positions, and microprocessor means cooperating with the product gas withdrawal sensing means, the oxygen sensor and the valve switching means having memory means provided with minimum selected product gas oxygen concentration limits at different withdrawal rates from said reservoir, respectively, and memory means provided with the minimum time required for charging each of said sieve beds to produce product gas having the minimum selected oxygen concentration at the sensed withdrawal rate, respectively, means for adjusting the timing cycle for operating said switching means for charging said sieve beds for the minimum time required to produce product gas having said minimum selected oxygen concentration at the sensed withdrawal rate, means for comparing the product gas oxygen concentration sensed by said oxygen sensor with said minimum product gas oxygen concentration limit at the sensed withdrawal rate, and means for further adjusting the timing cycle for switching said valve to increase the charging time of said sieve beds necessary to produce product gas having at least said minimum selected oxygen concentration at the sensed withdrawal rate. 20. In a process for selectively increasing the oxygen concentration of a gaseous mixture comprising switching a valve between a first position to charge atmospheric air under pressure from a compressor into a molecular sieve bed and selectively adsorbing nitrogen therefrom to produce an oxygen enriched product gas and a second position in which desorbed nitrogen is released from said sieve bed, directing said product gas to a reservoir, and withdrawing portions of said product gas from said reservoir, the improvement comprising: (a) determining the minimum time for charging said sieve bed to produce a minimum selected product gas oxygen concentration at a selected rate of withdrawal, (b) intermittently sensing the rate of withdrawal of product gas from said reservoir, (c) adjusting a timing cycle for switching said valve to said first and second positions for charging said sieve bed for said minimum time, (d) intermittently sensing the oxygen concentration of product gas withdrawn from said reservoir, (e) comparing the sensed oxygen concentration with said minimum selected product gas oxygen concentration, and (f) adjusting the timing cycle for switching said valve to increase the charging time when the sensed concentration is less than the minimum selected concentration. 21. In a process for selectively increasing the oxygen concentration of a gaseous mixture containing oxygen and nitrogen wherein a compressor alternately charges said gaseous mixture under pressure to a first and a second sieve bed, said sieve beds adsorbing nitrogen from said gaseous mixture to produce an oxygen enriched product gas and wherein said sieve beds are alternately charged by directing said gaseous mixture to a switching valve having a first valve position in which said compressor charges said first sieve bed and a second position in which said compressor charges said second sieve bed, and directing said product gas from said sieve beds to a reservoir, the improvement comprising, (a) providing a timing cycle for switching said valve to said first and second positions, (b) periodically determining the rate of withdrawal of product gas from said reservoir, (c) determining the minimum time required to charge each of said first and second sieve beds to produce a product gas having a minimum selected oxygen concentration at the rate of flow said product gas is withdrawn from said reservoir, (d) adjusting the timing cycle for switching the valve for charging said sieve beds for said minimum time, (e) periodically sensing the oxygen concentration of said product gas and comparing the sensed concentration with the minimum selected oxygen concentration at the sensed rate of flow, and (f) adjusting the timing cycle for switching said valve to increase the charging time when the sensed concentration is less than the minimum selected concentration. 22. In a process for selectively increasing the oxygen concentration of a gaseous mixture comprising switching a valve between a first position to charge atmospheric air under pressure from a compressor into a molecular sieve bed and selectively adsorbing nitrogen therefrom to produce an oxygen enriched gaseous product and a second position in which desorbed nitrogen is released from said sieve bed, directing said gaseous product from said sieve bed to a reservoir, and withdrawing portions of said product from said reservoir, the improvement comprising: monitoring the rate gaseous product is withdrawn from said reservoir, adjusting the timing cycle for switching said valve to charge said sieve bed for a minimum time necessary to produce gaseous product of a selected oxygen concentration at the monitored rate of withdrawal and switching said valve according to said adjusted timing cycle.