The continuous countercurrent flow (CCF) model for pressure swing adsorption (PSA) systems has so far been validated for Skarstrom cycle in which the pressurization and blowdown steps and adsorption and purge steps have equal durations. The mass balance was written in such a way that the total volumes of feed and purge were kept constant between the actual operation and the steady state CCF representation. By relaxing this restriction on the mass balance, it is shown that the usefulness of the CCF model may be extended to cycles in which the durations of the individual steps are different.