This 8 inch reduced pressure detector assembly with its exclusive design incorporating the patented air-in and water-out principle for protection from the reverse flow of fire protection system substances from being pumped or siphoned into the potable water supply due to backsiphonage and or backpressure in accordance with national plumbing codes and water authority requirements. Its compact modular design facilitates easy maintenance for in-line repairs. It is ideal for protection in continuous pressure piping applications and at cross-connections identified as health hazards and from other contaminants found at the service line entrance. This assembly without the shutoff valves consists of a cast iron body, captured spring check valves, replaceable seats, top mounted test cocks, a pressure differential relief valve, and comes furnished with a cubic foot per minute meter to detect underground leaks and unauthorized water use.