PSA is a nitrogen gas generator with the specially designed adsorbent. This adsorbent is called Carbon Molecular Sieves (CMS) having a micro pore in its surface and adsorb O2, CO2 and H2O molecular into such hall selectively under a certain pressure. After adsorption process, adsorbent is regenerated by depressurizing. PSA can produce the nitrogen gas continuously by repeating above adsorption and regeneration. For reference, PSA stands for Pressure Swing Adsorption.