Abstract: A device for separation of air from fiber suspensions of flotation devices which are heavily air- and foam-laden or represent a mixture of fluid and foam features a hydrocyclone whose inlet opening is arranged least 2.5 m below the outlet opening of the flotation device for the air-laden fluid or mixture. The separation section of the hydrocyclone is a slender, truncated cone-shaped body on whose pointed (thin) end the deaerated fluid is withdrawn. In this outlet opening there is a back pressure maintained, so that the inlet opening is not completely covered by the vortex of the fluid, leaving still a sufficiently free entrance cross section for the foam. Above the entrance section of the hydrocyclone a mechanical foam eliminator with a rotor is arranged, the rotor comprising an impeller wheel which is provided with radial blades. A funnel-shaped suction socket feeds the foam-air mixture to the impeller wheel.