VPSA means Vacuum Pressure Swing Adsorption. Feed air is sucked filters for removal of dust before boosted to 0.3~0.5barg by roots blower. It then goes into an absorber full of absorbent activated aluminum to eliminate water, CO2 and other gases at the bottom, above which N2 absorbed by absorbent zeolite molecular sieve. O2 with argon is output on the top as product gas into oxygen buffer tank and then boosted to higher pressure by oxygen compressor to consumption point.