Abstract: This invention relates to improvements in or relating to vacuum belt filters. It relates further to suction boxes for such filters and to a method of operation of the filters. More particularly, the invention relates to the supporting of the belt of the filter about the suction box so as to minimize drag of the belt and to minimize friction between the belt and the suction box and still seal the suction box. This is accomplished by means of conduits that have deformable walls and are located along the edges of the suction boxes, fluid support cushions being formed in the conduits. This is also accomplished by controlling the fluid support cushion according to the drag on the suction box, the suction pressure in the suction box and the rate of flow of fluid into the conduits to form the support cushion.