Abstract: A cyclone separator and an installation of such a separator in a processing vessel are set forth which conditions the inlet flow to prevent the depositing of particulates at the cyclone inlet. The separator is disposed in a cylindrical enclosure represented by the processing vessel. The enclosure has an inner surface and defines a chamber to receive the gas and entrained particulates. Disposed within the chamber is the smaller diameter cyclone separator having a cylindrical wall. To admit gas, the separator wall has an inlet, one side boundary of which is arranged tangential with the enclosure inner surface, the other side boundary being spaced from the surface to define an axially extending, scroll-shaped envelope between the enclosure inner surface, the cyclone wall and its inlet.