Abstract: Filtration apparatus, comprising two endless filter belts (1, 5) parallel to each other over one strand from a point where they come together, then moving away from each other over the remaining strand, a pair of facing plates (P1 to P10) between which the parallel strand passes, a mechanism (27) for temporarily moving the plates (P1 to P10) towards each other until the belts (1, 5) are clamped together for temporarily immobilizing the belts, a first means (2) for increasing the path of travel of the belts (1, 5) between the point where they come together and the pair of plates at the moment when the mechanism (27) immobilizes the belts by clamping them, and a second means (18, 23) for reducing the path of travel of the belts, at this same moment, between the point where they move away and the point where they come together.