Abstract: A device for filtering a liquid, particularly molten polymer, removes incompletely molten polymer, foreign matter, aggregates of various additives and the like from the molten polymer prior to further processing of the liquid such as extrusion through a spinneret plate. The device comprises a housing provided with a liquid inlet and a liquid outlet and, positioned between the inlet and the outlet, a filter pack built up of a number of filtering disks and supporting disks. The disks are so arranged the liquid to be filtered is caused to flow between a center portion and an outer surface of the filter pack. On the filter pack there is placed a piston for applying a compressive pressure to the pack. The piston is displaced and acts to compress the filter pack on a liquid supply side under the influence of the pressure of the liquid to be filtered.