A backflow preventer that includes a housing having an inlet and an outlet adapted to be mounted in a liquid flow configuration in a liquid supply circuit. An upstream check disc assembly is positioned in the housing downstream of the inlet, and includes an upstream check plate supporting a downstream diaphragm. An upstream check disc is positioned downstream of the diaphragm and integrally formed with an upstream stem mounted in an aperture in a central hub formed in the check plate for movement between an normally open, flow position and a closed position preventing backflow of liquid through the inlet. A downstream check disc assembly is positioned in the housing downstream from the upstream check disc assembly. A vent discharges liquid to atmosphere upstream of the downstream check disc assembly.