Cause of the pressure variation of the pressured air has the physical response with the molecular sieve in the pressure vessel. Cause of the different proliferation speed between Nitrogen molecular and Oxygen molecular the Oxygen molecular will be adsorption in the micron mesh shortly in the pressure-rise term. Make the Oxygen and the Nitrogen to be separated and swing outlet the Oxygen when pressure-less, this kind of motion is called PSA. (Pressure Swing Adsorption)