Which type of backflow prevention device is required for a chemically treated boiler system on the potable water system?

The recommended backflow prevention device for a chemically treated boiler system on the potable water system is the Reduced Pressure Zone (RPZ) valve. An RPZ is specifically designed for high-hazard applications, such as when chemicals are introduced into the water supply.

In a chemically treated boiler, there is a significant risk of toxic or harmful substances being back siphoned into the potable water supply if there is a drop in pressure. The RPZ valve features two independently acting check valves with a pressure differential relief valve between them, which ensures that if either check valve fails, the downstream pressure will drop, allowing water to flow out of the valve and preventing any contaminated water from entering the potable system. This makes it an effective safeguard against backflow in high-risk scenarios.

In contrast, other devices listed may not provide adequate protection for such hazardous situations. For example, a double check valve can be used for lower hazard conditions but does not afford the same level of protection as an RPZ because it lacks the built-in relief valve to address potential contamination risks. Atmospheric vacuum breakers and pressure vacuum breakers are more suited for preventing back siphoning in non-hazardous applications, rather than dealing with the complexities of a chemically treated system.