A conveyor displaces a succession of identical screens along a closed annular path having a generally horizontal upper stretch and a lower return stretch spaced below the upper stretch. The delivery unit includes a fuel pump arranged in a swirl pot, a fuel filter arranged downstream of the fuel pump, and a valve arranged in the swirl pot. The system further includes a radiation directing device that is selectively positionable to reflect the radiation beam in a desired direction and exposure the radiation-sensitive material to the radiation beam.