Abstract: Apparatus for pumping or conveying fluent material such as grain, sand, concrete, etc. is disclosed. The apparatus comprises a tube having an inlet at one end and an outlet spaced from the inlet and a pair of helical blades of opposite pitch mounted inside the tube for rotation relative to one another. One blade is mounted to a shaft extending axially inside the tube, and the other blade is mounted to the inside of the tube. The blades are interrupted at diametrical locations to enable the blades to move relative to one another as the shaft rotates relative to the tube for conveying fluent material. Preferably, the assembly is mounted with its inlet in a hopper and its tube disposed upright to afford vertical conveyance of the fluent material through substantial distances.