The KOBOLD plastic flow meters model VKP operate on a special suspended float principle with cylindrical measuring tube and spring-loaded float with orifice. The float in model VKP-3... has slots moulded on the outside, which protect the instrument from soiling by depositing dirt particles. The danger of the float jamming is thus considerably reduced and soiled liquids with a particle size up to 400 µm can be measured without difficulty. In model VKP-2... a sharp-edged orifice in the float renders the instrument less sensitive to changes in viscosity.