An oxygen concentrator is controlled during start-up to rapidly shuttle the sieve beds between communication with the pump and atmospheric pressure, so the pressure in the sieve beds is relieved while the pump motor is starting up. After the start-up period, the sieve beds are alternately connected to the pump and atmospheric pressure for longer continuous periods.

A breath-synchronized concentrated-oxygen supplier comprising an oxygen concentrator for producing and storing oxygen-enriched gas, and a buffer tank having an inlet connected to the oxygen concentrator and an outlet for temporarily storing the oxygen-enriched gas obtained from the concentrator. A valve is mounted in the outlet of the buffer tank so as to control flow of the oxygen-enriched gas from the buffer tank to the respiratory system of a living body, the valve having a gas flow path that is open to the atmosphere. A sensor, provided for sensing the respiration of the living body, generates an output signal indicative of the inhalation and exhalation phases of the respiration. An input device, on which a ratio between the entire length of the inhalation phase and a specific end portion thereof is set is included as is a regulator responsive to the sensor and input device for detecting the duration of each inhalation phase in succession based on the output signal from the sensor. The regulator also opens the valve at the beginning of each inhalation phase, and maintains the open time of the valve based on a period determined by a combination of averaging the preceding inhalation durations and the ratio set on the input device. Oxygen-enriched gas is supplied to the living body during each inhalation phase except for the specific end portion thereof, and the buffer tank acts to make the initial flow rate of the oxygen-enriched gas higher than the steady flow rate thereof in each inhalation phase.

A compressed gas mixture, for example air, is passed through one of beds 12 and 14 of adsorbent that selectively adsorbs oxygen from the air. Unadsorbed nitrogen-enriched gas flows into a buffer vessel 28, from which product gas is withdrawn through pipeline 30. While one of the beds 12 and 14 is adsorbing oxygen for air the other is being regenerated, and during this period the communication between the beds is denied. At the end of a chosen period of time the beds are placed in communication with one another by opening valves 54 and 56. Then the bed that was previously being regenerated is placed in communication with the source of compressed air and the other bed regenerated. The period of intercommunication between the beds lasts for as long as it takes the volume of product gas as measured by an integrating flow meter 31 from the start of the preceding adsorption step to reach a chosen value. The apparatus is able to supply nitrogen of a chosen purity at a variable flow rate.

In a pressure swing adsorption process for the production of nitrogen enriched product gas from air, when the process is halted during a pressure equalization step, that is, with valves open to permit the flow of gas from one vessel to a second vessel, then the gas remaining in the vessels is exhausted to atmosphere by opening a further valve. This results in rapid return to the required purity of nitrogen enriched product gas on start-up of the process. Preferably, subsequent to opening the further valve, another valve is opened, thereby permitting nitrogen-rich product gas from a reservoir to flow through the vessels, thereby purging said vessels with nitrogen enriched product gas.

An oxygen concentrator for supplying enriched oxygen gas to an open breathing system of a human being or the like in synchronization with a breathing cycle of a patient is disclosed, comprising a thermocouple sensor and a control device for synchronizing the timing of opening an electromagnetic valve provided in the gas passageway with the beginning of an inhalation phase of the breathing cycle. The thermocouple sensor, located near the patient's nostrils detects the change in temperature of breathing air flow of the human being or the like and generates a detection signal indicating the instantaneous temperature of the breathing air flow. Thereafter, the control devices detects the beginning of an inhalation phase by comparing the successive two voltage levels of the detection signal. When the breathing cycle enters the inhalation phase, the control device opens the electromagnetic valve thereby permitting the flow of oxygen to the patient. Supplying oxygen only on the inhalation phase has the effect of remarkably increasing the efficiency of the oxygen concentrator moreover the detection signal is monitored to detect when the breathing cycle of the patient becomes irregular. Upon detection, the control device will supply oxygen continuously while giving an alarm signal so that emergency measures can be taken.