Abstract: A rotary device having an outer rotor having bearings on a first axis, an inner rotor mounted within the outer rotor having bearings on a second axis of rotation offset from the first axis, and in which both outer and inner rotors rotate together in unison and define a spacing between the rotors varying from a minimum to a maximum at respective positions on opposite sides of the rotors, an enclosure at least partially enclosing the rotors, defining an inlet port and an outlet port, an outer annular wall and a plurality of semi-cylindrical contact bodies on the outer rotor, and a like plurality of recesses of semi-cylindrical shape in section in the inner rotor, and there being partitions between the recesses, with head portions on the partitions having a radiussed outward surface, and two acute angle corners, one at each end of the head portion, respective recesses receiving respective abutments so that, upon rotation, any one body may move inwardly and outwardly of its respective recess as the spacing betwee