Abstract: For the reduction of capacity losses and heating in hydrodynamic working circuits, especially retarders, caused by undesired air circulation in emptied condition, it is suggested to introduce a certain quantity of a blocking medium into the working chamber. This blocking medium may be operating fluid, air, or a mixture of both, and can be introduced radially from the inside, from the outside, or from the center. It forms a blocking film by rotation of the bladed rotor wheel, which substantially prevents the circulation of air from one bladed wheel to the other.