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 QR48 PTFE scraper, drawing figure B, Wedeco part 37333. PTFE is used here because it removes deposit without scoring the quartz and is unaffected by continuous UV exposure. Wedeco was founded in Herford, Germany in 1976 and is now a Xylem brand.