Illinois Food Service License Practice Test

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What is the only completely reliable method for preventing backflow?

High pressure
Air gap
Check valve
Vacuum breaker

The correct answer is: Air gap

The air gap is the only completely reliable method for preventing backflow because it creates a physical separation between a water source and a potential contaminant. This separation ensures that even under conditions where backflow might otherwise occur, such as when water pressure drops, no contaminated water can siphon back into the clean water supply. The air gap must be at least twice the diameter of the water supply outlet to be effective, and this design inherently prevents any possibility of contamination as it requires a significant physical distance between the water sources. Other options, while useful in certain scenarios, do not provide the same level of security. High-pressure systems might temporarily mitigate backflow risks, but they can't guarantee complete prevention. Check valves and vacuum breakers can help reduce the risk of backflow, but they can wear out over time or fail, making them less reliable than a well-maintained air gap. Thus, the air gap stands out as the safest and most dependable method for protecting against backflow.