Abstract: Method and apparatus for regenerating a diatomaceous earth filter cake of a pressurized liquid filter system by liquidizing the diatomaceous earth filter cake formed on filter elements in the filter chamber of the system; by uniformly mixing with the liquidized diatomaceous earth the insoluble particles, or impurities, removed by the filter cake from liquid that has passed through the cake; and by reforming the fluid cake with the impurities uniformly distributed throughout the filter cake. The liquidizing of the filter cake and impurities and mixing of the diatomaceous earth and impurities result from oscillations induced in the liquid in the filter chamber by several cycles of rapid reversal of the flow of liquid through the filter chamber.