Abstract: A system for determining a leak flow of a vacuum system of a vacuum filter includes a controller for adjusting speed of a filtration media of the vacuum filter and/or for adjusting supply rate of slurry onto the filtration media. The system includes a pressure sensor for determining pressure difference affecting over the filtration media and a layer of the slurry carried by the filtration media, and a device for determining flow rate through a vacuum pump that maintains the pressure difference. The speed of the filtration media and/or the supply rate of the slurry is/are adjusted so that the slurry is fully saturated by liquid along a whole filtration area affected by the pressure difference. Thus, fluid flow through the layer of the slurry is negligible and therefore the determined flow rate is indicative of the leak flow of the vacuum system.