The dust-mixed conveying gas is started turning by transferring it into a separator by means of a spiral construction. Gas is forced in to rotate in the cyclone. Due to the centrifugal forces, dust parcisles are carried to the surroundings. Pushing the gas to inward from the backward crastes a vortex. The air is separated from the dust particle, which are forced downwards along a spiral way because of friction of the air against the wall.