What type of backflow preventer is best suited for high-hazard applications such as connecting a chemical dispenser to the potable water system?

For high-hazard applications like connecting a chemical dispenser to the potable water system, the best type of backflow preventer is a Reduced Pressure Zone (RPZ) backflow preventer. A backflow preventer is a device installed in a potable water system to prevent backflow or backsiphonage, which is the unwanted reverse flow of non-potable water or other substances into the potable water supply. Backflow can occur due to pressure differences or siphon effects. An RPZ backflow preventer provides the highest level of protection. It consists of two independently acting check valves with a pressure-regulated zone between them, maintained at a pressure lower than the supply pressure. If either check valve fails, the reduced pressure zone will activate a relief valve, discharging the potentially contaminated water to the drain, thus preventing it from entering the potable water system. Because of its robust design and ability to physically separate the potable water from potential contaminants, the RPZ is mandated in situations where a cross-connection poses a severe health risk. The double check valve assembly (DCVA) is a less robust alternative suitable for medium-hazard applications, while atmospheric vacuum breakers (AVB) and pressure vacuum breakers (PVB) are only suitable for low-hazard applications and cannot be used under continuous pressure.