The invention relates to a gas tank arrangement (27) for a breathing apparatus (1), comprising a gas tank (28), an inlet valve (29) for controlling a flow of gas into said gas tank, an outlet valve (31) for controlling a flow of gas out of said gas tank and towards a patient (2), and a control unit (35) for controlling said inlet and outlet valves to maintain the gas within said gas tank (28) at an overpressure for subsequent delivery to the patient (2). The control unit (35) is configured to always maintain the pressure in the gas tank (28) between a minimum pressure threshold value and a maximum pressure threshold value, wherein the minimum and/or maximum pressure threshold value is determined based on preset parameters relating to the tidal volume of the patient (2), the dynamics of said outlet valve (31), and/or a desired minimum and/or maximum flow of gas out of the gas tank (28).
