Dual check backflow preventer

A backflow preventer, comprising:

• (a) a housing having an inlet and an outlet, and adapted to be mounted in a liquid flow configuration in a liquid supply circuit;
• (b) an upstream check disc assembly positioned in the housing downstream of the inlet, and including an upstream check plate supporting a diaphragm positioned downstream thereof, wherein the upstream check plate is adapted to support the diaphragm on an downstream side of the upstream check plate, and includes an outer, annular face engaging the diaphragm, an outer plurality of flow ports for allowing liquid to pass through the check plate and downstream around a centrally-formed opening in the diaphragm, a central opening in the check plate, an integrally-formed hub positioned in the central opening in the check plate, and a plurality of spokes extending radially outwardly from the hub and defining a plurality of voids for allowing liquid to pass through the check plate and downstream around the centrally-formed opening in the diaphragm ;
• (c) the diaphragm including a peripheral annular rib and a central seal portion comprising a downstream, axially-extending intermediate support rib and an inner, radially-extending seal portion, the peripheral annular rib being captured in a seal channel of the housing, the axially-extending intermediate support rib engaging a downstream support ring adapted to limit downstream movement of the diaphragm, and the central seal portion engaging an annular inner wall of the housing to limit downstream movement of the diaphragm from a position radially inward from the intermediate support rib;
• (d) an upstream check disc positioned downstream of the diaphragm and integrally formed with a stem extending upstream from the upstream check disc and mounted in an aperture in the hub formed in the upstream check plate for movement between an normally open, flow position and a closed position preventing backflow of liquid through the inlet;
• (e) a downstream check disc assembly positioned in the housing downstream from the upstream check disc assembly, and including a downstream check disc integrally formed with a stem extending upstream thereof and mounted in an aperture in a central hub formed in a flow opening in a wall of the housing for movement between an normally open, flow position and a closed position preventing backflow of liquid through the outlet;
• and
• (f) a vent from the housing upstream of the downstream check disc assembly and downstream of the upstream check disc assembly to atmosphere.