What type of backflow preventer is categorized as a Reduced Pressure Principle device?

The correct answer is a Reduced Pressure Principle backflow preventer because this device is designed specifically to protect water supply systems from contamination resulting from backflow. It functions by maintaining two separate pressure zones: one upstream and one downstream of a pair of check valves. This arrangement ensures that if there is a drop in pressure in the system, the water does not flow back into the potable water supply, thus preventing contamination.

This type of backflow preventer is particularly effective in situations where there is a significant risk of backpressure, such as in industrial applications, and is mandated by various plumbing codes. The two check valves are configured to reduce the risk of backflow, while the pressure differential created creates an air gap that provides additional protection.

In contrast, the other options listed serve different purposes or do not provide the same level of protection against backflow. For example, a pressure vacuum breaker and an atmospheric vacuum breaker primarily address issues related to siphoning and do not function in the same dual-pressure zone manner as a reduced pressure principle device. Similarly, a double check valve, while providing some level of backflow prevention, does not incorporate the same comprehensive safety features that characterize a reduced pressure principle device.