The floating suction unit FDB-231 Model operates into vertical storage tanks of a certain height, for which you cannot install a single section unit. As for the FDB-221 Model, FDB-231 Model is designed to suck the clean product just below the product surface. This is in order to prevent the contamination of the product with sediments which settle on the bottom of the tank. Such a position of the suction surface is guaranteed by the presence of floating units, properly sized according to the weight of the arm and of the stored product.