Abstract: A closed loop method and apparatus for unloading particulate materials from a transport container into a supply bin is disclosed. Material is conveyed from the discharge manifold of the transport container via vacuum into a transfer unit. The transfer unit has a vacuum zone and a pressure zone. The material is transferred from the vacuum to the pressure zone within the transfer unit and is conveyed via pressure to a cyclone separator mounted upon the supply bin. The particulate materials are separated in the cyclone separator and dropped into the supply bin. The overhead stream from the cyclone separator on top of the supply bin is returned to the discharge manifold on the transport container. Excess pressure developed in the supply bin is relieved into the transport container. Excess pressure in the transport container is filtered before being vented to the atmosphere.