Abstract: A filter, especially suitable for liquids which are difficult to filter and comprising a closed cylindrical filter container (1) having an inlet (5) for the liquid to be filtered and an outlet (7) for the filtrate and enclosing a filter unit (3) comprising one or more filter elements (13-15) which are mounted substantially concentrically inside the filter container (1). At one end, preferably the bottom end in case of vertically standing containers, the filter container has a bottom cover (2) which can be opened, and the filter element or elements (13-15) are mounted so that they can be extracted from and be retracted to the filter container (1) through said cover (2). The filter unit may comprise several filter elements (13-15) formed as separate units and mounted concentrically inside each other. The filter elements are designed so that an inner filter element over a collar (16-18) carries and is sealed against the adjacent outer filter element.