Backflow preventers with intermediate atmospheric vent (herein referred to as the device) are installed in the plumbing system to prevent backflow into potable water supply lines when pressure is temporarily higher in the polluted part of the system than in the potable water piping. Devices covered by ASSE 1012-2021 have functional capabilities for preventing both backsiphonage and backpressure, and can operate under continuous or intermittent pressure conditions. These devices have two independently operating check valves separated by an intermediate chamber with a means for automatically venting it to the atmosphere and can be installed in the horizontal, vertical up, or vertical down orientations. The check valves are force loaded to a normally closed position and the venting means is force loaded to a normally open position.