Wiper flap for Hanovia medium-pressure ultraviolet disinfection systems. The flap is the flexible wiping element carried on the wiper assembly; it is the part that actually contacts the quartz sleeve and therefore the part that wears. The quartz sleeve is the only optical path between the lamp and the water, so any film of scale or iron on its outer surface cuts the delivered UV dose. The wiper sweeps the sleeve on a timed cycle to keep transmission at the design figure. Replaced at scheduled service, and worth checking whenever measured UV transmission falls without an obvious water-quality cause. Reference number 2279G-0610.