Vacuum pressure swing adsorption (VPSA) oxygen plants generally utilize the operating steps shown above to separate and enrich oxygen. In one cycle, each adsorption vessel needs to undergo five steps: "adsorption", "pressure reduction", "vacuum desorption", "Purging" and "pressure increasing".

(1) Adsorption

After mechanical impurities in the air is removed by the filter, it enters the adsorption tower through the Roots blower. The H2O, CO2, and N2 in the air stay in the adsorbent bed. Since O2 is absorbed little in the adsorbent, the O2 exiting in the vessel will be richer than other entering mixture, and it is discharged from the outlet of the tower. A portion of the oxygen produced by this step is sent to the buffer tank, and the remaining portion is reserved for the next step to regenerate and boost the pressure in the adsorption tower.

(2) Pressure Reduction

In the "pressure reduction" step, oxygen-rich gas passes along the vessel outlet into another one in the “pressure increasing” step, and the pressure goes up.

(3) Vacuum Desorption

At the end of the "pressure reduction" step, in order to desorb the impurities as much as possible, the tower must be evacuated and depressurized. The biggest difference between VPSA and PSA lies in this step, that is, the vacuum pump is used to further evacuate the adsorption tower, which causes the pressure in the tower to decrease when the impurities are released and discharged through the vacuum pump outside.

(4) Purging

In order to desorb the impurities of the adsorption tower more thoroughly, at the end of the "vacuum desorption" stage, a small amount of oxygen will be introduced from another high-pressure tower to revitalize the adsorbent in the tower, at which time the partial pressure of oxygen in the tower rises while impurities’ is further reduced so that the adsorbent is more completely regenerated, which is more conducive to the adsorption in the next cycle.

(5) Pressure Increasing

After "vacuum desorption" and “purging”, the adsorbent in the adsoption vessel is regenerated. At this time, the pressure in the vessel is lowered. In order to quickly recover the pressure for adsorption and ensure that the adsorption front does not move up too quickly, it is necessary to introduce enriched oxygen in the other adsorption vessel in "pressure reduction" step to increase the pressure. The pressure of the vessel reaches the requirements and is ready for the next adsorption cycle when the "pressure increasing" step is completed.

The switching of the above steps is mainly done by the control system and switch butterfly valves. According to the sequential order of each step , the control system switches butterfly valves to control the length of time during “adsorption”, “pressure reduction”, “desorption”, “purging” or “pressure increasing” processes in the adsorption vessel, achieving the separation of oxygen from nitrogen and finally obtaining the required oxygen.