Elastomer seals in an ultraviolet reactor work against warmth, pressure and direct UV exposure, which hardens and shrinks them over time. They are replaced whenever the joint is opened rather than reused: a seal that looks sound can still have taken a compression set that will not re-seat. Compound matters as much as size on a UV-exposed seal, so order against the position rather than measuring the old one. The matching TMO IV lens is stocked under item 13215-0215. Wedeco was founded in Herford, Germany in 1976 and is now a Xylem brand.