Abstract: In order to filter out of the dielectric the microscopically small spherical particles removed by spark erosion [???] machines, a labyrinth filter is provided, containing at least one filter unit with a pressure receptacle (21) loosely filled with filter grains. The intake surface area is relatively small by comparison to the height of the column through which the liquid to be filtered flows, and the filter pump is matched to these two dimensions in such a way as to cause the dielectric to flow through the labyrinth at a rate of at least 2 meters per minute. This leads to the formation of low-pressure zones behind the individual filter grains, in which zones the microscopically small spherical particles removed by the erosion [???] process become trapped.