One of the methods employed to prevent backflow and control the cross connections is the:

The pressure vacuum breaker is an effective method for preventing backflow and controlling cross-connections in water systems. It works by utilizing an atmospheric vent that allows air to enter the pipeline when there is a drop in pressure, which prevents the possibility of a backflow of contaminated water into the potable water supply.

When a negative pressure occurs in a water line, perhaps due to a sudden demand or a malfunction, the pressure vacuum breaker automatically opens the vent to allow air to enter, maintaining a pressure differential that stops backflow. This device is particularly useful in irrigation systems and other scenarios where there is potential exposure to non-potable water.

In comparison, while the air gap creates a physical separation to prevent backflow, it can be impractical in many systems. Backflow preventers and check valves also serve their roles, but the pressure vacuum breaker excels in situations where maintaining airflow is critical in preventing backpressure conditions. Thus, this device is widely recognized for its ability to mitigate the risk of contamination due to backflow.