Atlantium MP0000406 — O-ring, size AS568-050 (inside diameter 133.07 mm x cross-section 1.78 mm; 5.239 in x 0.070 in), NBR (nitrile), compound N6001. Sealing elements are replaced at every lamp or quartz service, because elastomers take a compression set at the operating temperature of a medium-pressure lamp. Fit dry or with a UV-system-approved lubricant and confirm the groove is free of scale before assembly. Spare part for Atlantium Technologies Hydro-Optic (HOD) UV water disinfection systems, which use medium-pressure lamps, a quartz treatment chamber working by total internal reflection, one UV intensity sensor per lamp and continuous UV-transmittance monitoring; installed in aquaculture, dairy and beverage process water, municipal drinking water, power-plant and industrial water treatment.