Abstract: An apparatus is disclosed which is useful in simulating the countercurrent flow of several fluid streams through a bed of solid contact material such as a selective adsorbent. The apparatus comprises a plurality of multi-port valves and is used to direct the flow of different streams into and out of a fixed bed of material at points which are periodically changed. The invention arises in the arrangement of the valves, which minimizes the number of required valves and also minimizes the undesired admixture of different streams in the process lines connecting the contacting bed to the main fluid transfer lines. The valves are arranged in three tiers, with the first tier having sets of valves arranged in series flow and the second tier having sets of valves arranged in parallel . The third tier of valves directs flows between two adjacent fluid feed or withdrawal conduits entering the contacting bed.