Wedeco reactors with a wiper sweep the outside of the quartz sleeve to remove the scale and film that attenuate UV-C before it reaches the water. A wiper that is worn or wiping unevenly shows as falling measured intensity on lamps that are themselves still good. This is the wiper holder for 48 mm sleeves, drawing figure A, Wedeco part 39409. The holder sets the pressure the wiper ring bears on the sleeve: too little and deposits survive the sweep, too much and ring and sleeve both wear. Replace holder and ring together. Wedeco was founded in Herford, Germany in 1976 and is now a Xylem brand.