Pressure Swing Adsorption (PSA) is a technology used to separate some gas species from a mixture of gases under pressure according to the species' molecular characteristics and affinity for an adsorbent material. It operates at near-ambient temperatures and so differs from cryogenic distillation techniques of gas separation. Special adsorptive materials (e.g., zeolites) are used as a molecular sieve, preferentially adsorbing the target gas species at high pressure. The process then swings to low pressure to desorb the adsorbent material.
Generally The Pressure Swing Adsorption units come as a packaged unit. These are transported to the site as one or more pieces ready to be installed.

A Typical Pressure Swing Adsorption unit consists of the following equipment:
● Adsorber Vessels that are made up primarily of carbon steel that are filled up with Adsorbents.
● Valve and piping skids that includes instrumentation also. Generally these comes as prefabricated.
● A PSA Control System that is located in the remote control room is used for controlling cycles.
● A Mixing drum that is employed for minimisation of the composition variation of the offgas.

In a Refining industry a PSA unit has ably replaced the Carbon dioxide removal unit along with methanator and allows the plant to produce hydrogen with optimum purity. PSA Hydrogen gas plants contains a Steam Methane Reformer that is followed by high temperature super conductors. The PSA unit then purifies the syn gas effluent from the HTSC. The final product that is got comes with 99.99% purity. The offgas stream produced by the PSA unit is used by the steam Methane reformer as the primary fuel source. The added benefit of purity because of the PSA units has its benefits in the down stream units.

Pressure swing adsorption processes rely on the fact that under pressure, gases tend to be attracted to solid surfaces, or "adsorbed". The higher the pressure, the more gas is adsorbed; when the pressure is reduced, the gas is released, or desorbed. PSA processes can be used to separate gases in a mixture because different gases tend to be attracted to different solid surfaces more or less strongly.
This is exactly the process used in portable oxygen concentrators used by emphysema patients and others who require oxygen enriched air to breathe.
Using two adsorbent vessels allows near-continuous production of the target gas. It also permits so-called pressure equalisation, where the gas leaving the vessel being depressured is used to partially pressurise the second vessel. This results in significant energy savings, and is common industrial practice.