Wiper ring, 38 mm diameter, for Hanovia PMD, SPA and BMD medium-pressure ultraviolet disinfection systems. The ring bears on the quartz sleeve and sweeps it clear on each wiper cycle. 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. This range uses two quartz sleeve diameters, 38 mm and 47 mm; the rings are not interchangeable and the 47 mm ring is a separate item. Reference number 2242-0707.