A liquid storage tank has a breathing valve that vents the tank's headspace at a high-pressure value and admits an ambient gas at a low-pressure value. A controller generates a first control signal when the percentage of the catalyst gas is less than a catalyst threshold, a second control signal when the percentage of the catalyst gas exceeds the catalyst threshold, and a third control signal when the pressure in the headspace is equal to a low-pressure threshold between the breathing valve's low-pressure value and high-pressure value. The first valve is only opened to output inert gas at a discharge pressure greater than the breathing valve's high-pressure value in response to the second control signal. The second valve is only opened to output inert gas at a discharge pressure that is between the breathing valve's low-pressure value and high-pressure value in response to the third control signal.