In accordance with some embodiments, margining routines to determine acceptable voltage command values for specific CPU implementations at one or more different operating levels may be provided. Each of the plurality of composite magnetic particles has a ratio Rmc of a maximum diameter to a circle-equivalent diameter of more than 1. According to the invention, another valve, that is built-in in the valve body, is provided since the latter is hollow in order to receive a further valve body that is displaceably arranged for interaction with a further valve seat.