What type of backflow prevention is required for a closed-loop system that contains antifreeze?

The requirement for a Reduced Pressure Zone (RPZ) backflow prevention device in closed-loop systems containing antifreeze is rooted in the need for protecting potable water supplies. In such systems, there is a risk that the antifreeze or other contaminants could backflow into the drinking water supply, particularly under conditions that might lead to a loss of pressure, which can create a siphoning effect.

RPZ devices provide a higher level of protection compared to other backflow prevention methods, such as double check valves or atmospheric vacuum breakers. They are specifically designed to handle situations where harmful substances might be introduced into the potable water system. The RPZ operates with two check valves and a pressure differential relief valve that maintains a constant pressure, ensuring that any backflow is contained and cannot contaminate the drinking water supply.

In contrast, while double check valves are effective in many scenarios, they may not provide sufficient protection against backpressure conditions, which are critical in a closed-loop antifreeze system. Atmospheric vacuum breakers offer limited protection and are not appropriate for systems that can contain toxic or hazardous substances. As such, using an RPZ is the most effective method for safeguarding potable water in these situations.