The protection of data on a client mobile computing device by a server computer system such as within an enterprise network or on a separate mobile computing device is described. There is at least one fluid inlet extending through the bottom wall into the barrel, a fluid outlet in the side wall of the barrel, and a valve cartridge seated in the barrel. To improve the changeover process of a casting tube and to make it safer, the displaceable closure plate carries a connecting ring for the centered accommodation of the casting tube and the displaceable closure plate carries a changing device for the casting tube.