Abstract: Gas separation by pressure swing adsorption (PSA) and vacuum pressure swing adsorption (VPSA), to obtain a purified product gas of the less strongly adsorbed fraction of the feed gas mixture, is performed with an apparatus having a plurality of adsorbers. The adsorbers cooperate with first and second valve means in a rotary PSA module, with the PSA cycle characterized by multiple intermediate pressure levels between the higher and lower pressures of the PSA cycle. Gas flows enter or exit the PSA module at the intermediate pressure levels as well as the higher and lower pressure levels, under substantially steady conditions of flow and pressure. The PSA module comprises a rotor containing laminated sheet adsorbers and rotating within a stator, with ported valve faces between the rotor and stator to control the timing of the flows entering or exiting the adsorbers in the rotor. Feed gas is compressed prior to entry to the first valve means.