FILTER

A flat bed filter in which a filter medium in strip form is supported on an endless conveyor and supports a pool of contaminated liquid to be filtered. The conveyor is periodically advanced to provide fresh filter medium for filtering the contaminated liquid. The underside of the conveyor communicates with an evacuated compartment which is separated into separate chambers by a transverse partition. The transverse partition is in sealing engagement with the underside of the conveyor that advances the filter medium, and a means is provided for maintaining the chamber nearest the supply of filter medium at a higher pressure than the adjacent chamber in order to reduce the flow rate of contaminated liquid through the portion of filter medium initially exposed to the pool of liquid to be filtered.