a hydraulic anti - vibration device includes two rigid frame members , an elastomer body , two sealed chambers , a constricted passage putting the two sealed chambers into communication with each other , a valve member that defines portions of the two chambers and that has an axis of revolution , and two grids between which the valve member is interposed . the grids limit displacements of the valve member . interposed non - uniformities cause the amount of contact the valve member has with a grid to vary progressively and angularly around the central axis of the valve member . the non - uniformities are disposed around the central axis in a distribution that is angularly non - repetitive .