Backflow Prevention Practice Exam

Which backflow prevention method creates a physical barrier to contamination?

1. Vacuum breaker

2. Air gap

3. Pressure differential system

4. Check valve

The correct answer is: Air gap

The air gap is a backflow prevention method that establishes a physical barrier between the drinking water supply and any potential contaminants. This method involves maintaining a vertical distance between the water outlet and the flood level of the receiving vessel or drain, which effectively prevents any backflow due to pressure changes or siphoning. By creating this gap, any contaminants that might enter the water system cannot reach the potable water supply, as they would need to physically overcome the height of the air gap. This is particularly effective in applications where there’s a risk of wastewater or other polluted water coming into contact with potable water supplies, making it one of the most reliable methods for preventing backflow. Other methods mentioned do have their own merits but do not create a physical barrier. For example, a vacuum breaker relies on air pressure changes to stop backflow but does not establish a physical separation. Pressure differential systems and check valves utilize mechanical means to prevent reverse flow, but these systems can fail under certain conditions, whereas the air gap remains effective as long as it is properly maintained.