An apparatus for converting rotation to fluid flow, comprising a fluid conduit coiled around a rotational axis, the fluid conduit having a first inlet for receiving first fluid having a first density and a second inlet for receiving second fluid having a second density, and a first outlet for output of first fluid and a second outlet for output of second fluid; a motor coupled to the fluid conduit to rotate the fluid conduit around the rotational axis in a first angular direction such that first fluid portions of first fluid and second fluid portions of second fluid are transported along the fluid conduit towards the first outlet, while being pressurized; and a fluid returning arrangement, fluid flow connecting the second outlet and the second inlet for selectively allowing pressurized second fluid to return from the second outlet to the second inlet, while depressurizing the pressurized second fluid.