The reduced pressure principal device consists of two independently acting check valves with an automatic operating _______________ valve located between the two check valves.

The reduced pressure principle device is designed to prevent backflow and is a crucial component in maintaining safety in water supply systems. The key feature of this device is the use of two independently acting check valves, which create a physical barrier to backflow.

The automatic operating valve that is installed between these two check valves is known as a pressure differential relief valve. This specific valve plays a vital role in monitoring the pressure within the system. If the pressure in the downstream side of the first check valve falls below the pressure in the upstream side of the second check valve, the pressure differential relief valve opens, allowing any backflow or undesirable flow to be diverted, thereby protecting the potable water supply.

By utilizing this configuration, the reduced pressure principle device ensures that backflow does not contaminate the clean water supply, which is critical for public health. Other options do not accurately describe this automatic valve's function within the device. While a relief valve may seem similar, it typically serves different purposes in various systems, such as preventing overpressure, rather than specifically managing pressure differentials related to backflow prevention.