Replacement ballast for the Willand AT 42/20 ultraviolet disinfection system. The ballast drives the low-pressure UV lamp at the correct current and voltage, so lamp life and delivered disinfection dose depend on it operating within its rated window. Supplied as the OEM part for like-for-like replacement during service. Reference number 2838-0810. Contact us if you are unsure whether this ballast fits your specific UV system revision.