Which backflow prevention method involves two check valves with a relief valve in between?

The method involving two check valves with a relief valve in between is the reduced pressure principle device. This device is specifically designed to prevent backflow by utilizing a configuration that provides an additional layer of protection against potential contamination of the water supply.

In this setup, the two check valves help to minimize the risk of backflow under standard operating conditions, while the relief valve serves as a crucial safety feature. It opens to discharge any excess pressure that could occur if the upstream pressure falls below the downstream pressure, effectively preventing backflow in the event of a reverse pressure situation. This design is particularly effective in situations where there is a risk of contamination from pollutants or hazardous materials.

Understanding the reduced pressure principle device is key to ensuring safe water supply systems, as it greatly enhances protection against the possibility of backflow in various plumbing scenarios.