A gas tank arrangement for a breathing apparatus, including: a gas tank； an inlet valve configured to control a flow of gas into said gas tank； an outlet valve configured to control a flow of gas out of said gas tank and towards a patient； and a controller configured to control said inlet and outlet valves to maintain the gas within said gas tank at an overpressure for subsequent delivery to the patient, to control the outlet valve based on a parameter that is indicative of pressure within the gas tank, and to control the inlet and outlet valves to always maintain the pressure in the gas tank between a minimum pressure threshold value and a maximum pressure threshold value, wherein the minimum or maximum pressure threshold value is determined based on preset parameters relating to the dynamics of said outlet valve, or a desired minimum or maximum flow of gas out of the gas tank.
