Which of the following devices is commonly used for backflow prevention?

The double check valve is a widely used device for backflow prevention. It consists of two independently acting check valves that work together to provide a reliable barrier against the reverse flow of water. This device is specifically designed to protect potable water supplies from contamination due to backflow, which can occur when there is a sudden change in water pressure, allowing non-potable substances to enter the clean water supply.

The double check valve is particularly effective in moderate hazard situations where there is a potential for contamination, making it a suitable choice for many applications, including irrigation systems and industrial processes. Its construction allows for easy maintenance and functionality, as it can be tested for effectiveness without interrupting the water supply.

In contrast, devices such as pressure relief valves and flow control valves serve different functions. A pressure relief valve is primarily designed to relieve excessive pressure in a system, while a flow control valve regulates the flow rate but does not prevent backflow. The riser valve also does not function as a backflow prevention device; instead, it typically controls the flow and direction of water in vertical piping. Therefore, the double check valve stands out as the most appropriate choice for preventing backflow in various applications.