The filter element of the KLASS cyclone filter is a fixed filter tube. It is located in the centre of the housing into which the contaminated liquid flows tangentially at high speed. Heavy solid particles are separated by the centrifugal force in the rotating liquid column and thus do not load the filter element. Only the light solids settle on the filter tube. A hydrodynamic scraper rotating around the filter element continuously cleans the filter tube by suction. This ensures optimum filter performance at all times and also maintains the circulation of the liquid.