Abstract: The invention relates to a rotation device, such as a pump or a hydromotor of the rotating type, wherein a rotation-symmetrical rotor bounds at least two rotor channels together with radial baffles. The rotor comprises two generally goblet-shaped dishes, the innermost dish of which is stiffened by a first stiffening plate which has a peripheral widening, for instance branches in its peripheral zone into at least two rings which are rigidly connected with at least two respective bent peripheral edges, substantially over the whole outer surfaces thereof, to the inner surface of the peripheral edge of the relevant dish such that the stiffness of the peripheral edge of the dish is increased.