A filter plate assembly for a filter press, comprising: a filter frame defining a closed perimeter delimiting an open space, a filter plate supported on the filter frame such that the filter plate extends over the open space, a retainer groove provided on a side of the filter frame facing the filter plate (3, and a diaphragm extending over the open space, and attached to the filter plate assembly, between the filter frame and the filter plate, the diaphragm further comprising: - on a side facing the filter frame, a seal bead for sealing the diaphragm against the filter plate, and - on a side facing the filter plate, a retainer bead received within the retainer groove, such that the diaphragm is retained in position between the filter frame and the filter plate, wherein the filter frame forms a lateral wall of a filter chamber, when in use, characterized in that the seal bead comprises a first seal lip and a second seal lip, wherein the first seal lip is vertically elevated from the second seal lip, wherein the filter plate is arranged on the filter frame so as to allow a limited vertical travel of the filter frame with respect to the filter plate, such that the filter frame has: - a lowermost position, in which only the first seal lip is in contact with the filter plate, and - an uppermost position, in which both the first seal lip and the second seal lip are in contact with the filter plate. a filter frame defining a closed perimeter delimiting an open space, a filter plate supported on the filter frame such that the filter plate extends over the open space, a retainer groove provided on a side of the filter frame facing the filter plate (3, and a diaphragm extending over the open space, and attached to the filter plate assembly, between the filter frame and the filter plate, the diaphragm further comprising: - on a side facing the filter frame, a seal bead for sealing the diaphragm against the filter plate, and - on a side facing the filter plate, a retainer bead received within the retainer groove, such that the diaphragm is retained in position between the filter frame and the filter plate, - on a side facing the filter frame, a seal bead for sealing the diaphragm against the filter plate, and - on a side facing the filter plate, a retainer bead received within the retainer groove, such that the diaphragm is retained in position between the filter frame and the filter plate, wherein the filter frame forms a lateral wall of a filter chamber, when in use, characterized in that the seal bead comprises a first seal lip and a second seal lip, wherein the first seal lip is vertically elevated from the second seal lip, wherein the filter plate is arranged on the filter frame so as to allow a limited vertical travel of the filter frame with respect to the filter plate, such that the filter frame has: - a lowermost position, in which only the first seal lip is in contact with the filter plate, and - an uppermost position, in which both the first seal lip and the second seal lip are in contact with the filter plate. - a lowermost position, in which only the first seal lip is in contact with the filter plate, and - an uppermost position, in which both the first seal lip and the second seal lip are in contact with the filter plate.