Filter element, filter, and filter system with return line bypass

The invention relates to a filter (12) for filtering a medium, in particular an aqueous urea solution to be filtered. The filter (12) has a filter element (18) with a filter material (30). The medium can be pumped at least partly, preferably completely, out of the filter (12) without passing the filter material (30) such that dirt filtered out of the medium is not released from the filter material (30) and pumped out together with the medium. For this purpose, the filter (12), in particular the filter element (18), is provided with a non-return element (36) such that a flow of the medium from the unfiltered side (32) to the clean side (34) of the filter (12) is blocked but a flow of the medium from the clean side (34) to the unfiltered side (32) of the filter (12) is possible. The non-return element (36) is preferably designed in the form of a mushroom-shaped membrane (42). The membrane (42) is additionally anchored in a continuous recess (46) of the filter (12) preferably by a thickened portion (48) in the b