For filtering and separating liquid and gaseous media, particularly for water desalinization by reverse osmosis, modules filled with membrane cushions are employed that are open at two opposite sides and are inundated within an outer housing by an entering medium. The medium which enters into the interior of the membrane cushion is led away by means of aligned cushion holes and a conduit located in these holes. According to the invention, it is proposed that where there is a tandem series of several membrane cushion modules in a common housing, the stacked modules not be connected securely to one another and that a turbulence producing gap between them be permitted so that undesirable operational behavior does not occur in the form of pressure waves, pressure surges and blockage action with changes in the rate of flow and particularly upon starting the system for the first time.