Very often in the food packaging industry, a cylinder with a Varying bore diameter is used in hygienic dispensing Applications. A piston operates inside the cylinder where there are small clearances and the seal interferes with the Cylinder wall .During the cleaning cycle the piston is actuated to a region of the cylinder where the bore diameter is increased to ensure that there is clearance between it and the cylinder bore. This allows cleaning fluids to encompass the whole of the piston assembly and seal.