Abstract: Each group of conical cyclone separators is arranged in an annular block with their longitudinal axes in a common plane, each side of each block having concentric sealing surfaces coacting with corresponding sealing surfaces of an adjacent similar block to seal against leakage from an inlet opening for supplying the separators. Preferably, the stack of blocks surrounds a central shaft for clamping the blocks together and forming a discharge path for the heavier constituent from the separators, the lighter constituent discharging from the separators at the outer periphery of the stack into a chamber surrounding the stack.