the inner side of the floor all around in a sealed manner to the same the inlet nozzle 4 is slightly offset to the rear so that the incoming liquid cannot flow more strongly into the upper inlet openings at the outlet end of the double wall chamber the inner square pipe is fitted into the separating wall 7 which is a laser cutting with a plate thickness of 1 5 mm and welded to the same the shape of the separating wall 7 is shown by fig2 a the inner pipe itself consists of two lasered 1 5 mm plate halves which are canted with a defined radius and are to be welded together at an intended narrow bordering 18 the configuration 19 shown in fig2 in a sectional view of the nine provided uv low pressure radiation sources or lamps has been used in the construction in a consistent and aligned manner starting from floor 6 in the collecting shield 20 according to fig2 c and in the flow screen 21 according to fig2 d the cladding tubes 14 are inserted and held in the flow screen 21 and a baffle plate 27 is also lasered into the same the middle radiator holder 20 has the.