Abstract: A separator for use in installations for conveying objects over distances by means of a flow of air, the separator including a generally cylindrical separator grid within a casing, and a spiral grid portion extending outside the cylindrical grid. The spiral grid portion is tangential to said cylindrical grid and to the outside wall of an inlet pipe for admitting a mixture of air and objects. The cylindrical grid and the spiral grid portions permit the passage of air, but not the objects. An adjustable flap is pivoted on the line of intersection between the inside wall of the inlet pipe and said cylindrical grid for controlling the flow of air and objects entering the separator. The spiral grid portion has a rough surface exposed to the gas flow.