The end flange closes the ultraviolet reactor and is part of its pressure boundary. It also locates the quartz sleeve and, through it, the lamp — so flange condition governs both watertightness and whether the lamp sits on the axis the reactor was dosed around. Flanges are ordered against a specific reactor size and are not interchangeable between them. This is the flange for the InLine 1000. Quote the reactor serial number when ordering if the plant has been retrofitted, as flange detail changed across build standards within a single model number.