The packing for food such as folded cardboard boxes and cartons for frozen vegetables, sweets or crisps are printed colourfully and effectively for advertising purposes. Printing is often carried out near the place where filling of the respective product takes place. In order to achieve good printing results and / or to avoid permanent soiling of the machine by dried up ink the inking units must be supplied with the required ink colour during the inking procedure and then be cleaned and the ink must be completely removed. These processes can also be automatized and the different inks and cleaning agents are then controlled by valves. As even the slightest ink residues after changing the colour can lead to serious misprints, the valves must have minimum deadlegs and be easily cleanable without leaving residues.