Metal working oils are usually clarified and fed back to the process involved. Pre-coat filters or simple vacuum belt filters with non-regenerable, nonwoven filter media are often used to purify such liquids. This involves permanent extra costs for the unit operation. The concept of using periodically backflushed expandable filter candles has been demonstrated as a successful alternative. The filter principle is based on filter candles consisting of an expandable stack of paper rings. The MVM Institute in Karlsruhe and the Transor Filter GmbH Company have initiated a joint research project to analyze the complex filtration mechanisms and to optimize this filtration system. Filter experiments, CFD simulations and theoretical considerations should result in a reliable model for the prediction of the filter process for practical use and improve the present state-of-the-art in the area.