Abstract: An arrangement and method for mechanical cleaning of an active surface (4,17-20) of an instrument (5) in touch with liquid. The active surface of the instrument is exposed to cleaning media (11), which consists of separate, moving particles, enclosed into an instrument container. The motion of the cleaning media is rotational and achieved and maintained by directing an influx (9) parallel to the direction of motion (8) of the cleaning media. The influx may contain gas, liquid or mixture of gas and liquid. The cleaning media wipes clean the at least one active instrument surface.