Abstract: A rotary valve for feeding bulk material comprises a housing having a cavity, a supply opening leading to said cavity, and a discharge opening. Within the cavity, there is a cellular wheel rotatably supported. The distance between the outer circumference of the cellular wheel and the inner wall of the cavity can be altered. At least one sensor determines the distance and provides an output signal representative for it. Either the cellular wheel or the inner wall of the cavity or both are at least locally deformable in dependence on the output signal. In addition, the invention relates to a method or operating a cellular wheel where the above-mentioned distance or gap is determined or measured and at least one of said inner and outer radial dimensions of the cellular wheel and the cavity are controlled accordingly.