The present invention relates to an apparatus for converting rotation into fluid flow and/or fluid flow into rotation. The apparatus comprises a first coiled fluid conduit and a second coiled fluid conduit and a fluid separator for separating a first fluid from a second fluid having a second density different from the first density. The fluid separator is configured in such a way that when, during rotation of the fluid conduits first mass portions of the first fluid and second mass portions of the second fluid are alternatingly transported by the first fluid conduit into or from the fluid separator, third mass portions of the first fluid and fourth mass portions of the second fluid are alternatingly transported from or to the fluid separator by the second fluid conduit. A ratio between each of the first mass portions and each of the second mass portions is substantially greater than a ratio between each of the third mass portions and each of the fourth mass portions. This provides for a net flow of one of the first and second fluids through the apparatus.