Horizontal Belt Vacuum Filters are used in continuous, horizontal vacuum belt filters for the chemical process industries. It has multi-step processing capability in a single machine. It has agitators in the form of rotatable shafts provided with radial vanes, which are arranged transversely above the belt upper run so that the vanes break up the filter cake formed thereon. These agitators are mounted within a cover which is open downwards towards the belt and are supplied with treatment liquid. Filter cake portions removed from the belt are carried around by the rotating vanes and subjected to the additional liquid before being redeposited upon the belt and carried along therewith as the belt progresses.