What are the three types of backflow prevention methods?

The correct answer identifies three widely recognized methods for preventing backflow: air gap, double check valve, and reduced pressure principle.

An air gap is a physical separation between a water source and a potential contaminant, ensuring that water cannot flow back into the supply line. It is one of the most effective ways to prevent backflow, providing a clear distance that eliminates the risk of contamination.

The double check valve consists of two independent check valves installed in series. This design provides an additional layer of protection against backflow by allowing one valve to detect any reverse flow and close off, while the other can serve as a backup. It's commonly used in applications where there is a moderate risk of backflow.

The reduced pressure principle is a more advanced mechanism that uses a relief valve to discharge any potential backflow, essentially maintaining lower pressure in the protected area compared to the supply line. This highly effective method is often used in situations involving cross-connections with hazardous substances.

In contrast, other options either include components that are not effective for backflow prevention, such as a swing-check valve or gate valve, or do not accurately represent recognized methods in plumbing and water supply safety. Thus, the combination of air gap, double check valve, and reduced pressure principle encompasses the