The mechanical load of the relatively expensive conveyor belt is too high for large heavy lumps (40 to 300 mm), so that it would have to be replaced fairly often owing to the large amount of abrasion. To overcome this problem, the material is fed via a sturdy chute into the detection area, which is directly below the edge of the chute. Detection and sorting is carried out according to the same principles as already described above, whereby a much larger quantity of air is required from the high precision valves for throughput because the particles are more difficult to sort.