Triple purpose inbuilt by-pass for rapid filling of the boiler. The AB-40 boiler feed valve features an all brass body, inbuilt strainer, special heat resistant diaphragm and seat disc. The AB-40 pressure reducing boiler feed valve contains an inbuilt check valve in the supply inlet, which provides a positive means of preventing backflow of contaminated boiler water in the home water supply. Assembled and tested in the USA.