A method for controlling an oxygen liquefaction device includes measuring a flow rate from an oxygen concentration subsystem to a liquefaction subsystem, comparing the flow rate to a flow rate setpoint, and adjusting a cycle timing of the oxygen concentration subsystem in accordance with the comparing. A device for producing liquid oxygen, includes an oxygen concentrator, a liquefaction system, that receives oxygen enriched gas from the concentrator, and condenses it to produce a liquid product. The device further includes a liquid product storage tank, a sensor, that measures a flow rate from the oxygen concentrator to the liquefaction system and a controller that adjusts an oxygen concentrating cycle time in response to the measured flow rate.
