The PRESSURE RECOVERY is defined as the pressure rise realized by secondary product gas relative to the pressure rise after total repressurization. The APPARANT PRESSURE RECOVERY (APR) is defined similarly except that the adsorber vessels are assumed to contain only nonadsorbents (zero capacity), all at the same temperature and only filled by a perfect gas and further neglecting adiabatic thermal effects on pressure changes. Different PSA systems may be compared on an equal basis in terms of their APR-values without having to resort to lengthy calculations.
For instance, for two adsorber vessels exchanging gas and during this step excluding any slipsteam until pressure equilibration and further continuing repressurization only with slipstream until maximum pressure is obtained, under above assumed conditions the APR-value is 50 %, however if some external slip stream contributes to the pressure rise of the gas receiving adsorber during the gas exchange, the equilibrium pressure will be higher, resulting into a lower APR-value, because less (secondary product) gas from the gas releasing adsorber will have contributed in the pressure rise of the gas receiving adsorber.
Below some examples of typical APR-values are given for a number of PSA adsorber configurations.