PURPOSE: To permit a thick sealing effect and a separating effect by a method wherein a grease separating chamber is constituted by a part of a casing to miniaturize it and the perticle of the grease mixed with compressed gas in the grease separating chamber is separated and retrieved to supply it to a gear rotor.

CONSTITUTION: The grease separating chamber 5 is constituted by a part of the horizontal casing 2 to miniaturize it. The perticle of grease, mixed with the compressed gas, is pushed out from the upper opening 4 of the casing into the separating chamber 5, however, the molecular weight of the grease G is larger and, therefore, the grease is separated from the gaseous body, the speed of which is attenuated in the separating chamber 5, dropped onto a block of the grease G on a grease pan 11 to retrieve it, the surface part thereof is softened by the temperature of the compressed gas again and is supplied from both blades 14, 14' to the peripheral surfaces of the gear rotors 9, 9' under a dropping condition to seal the gap S between the gear rotors 9, 9' and the casing 2 by the grease sealing. Thus, the thick sealing effect and the separating effect may be permitted by the circulation of the grease G and the grease sealing.