Backflow Prevention Practice Exam

What hydraulic condition can a pressure vacuum breaker tolerate without failure?

1. Positive pressure on the inlet side

2. Negative pressure at the outlet

3. Stable atmospheric pressure

4. Variable water temperatures

The correct answer is: Stable atmospheric pressure

A pressure vacuum breaker is specifically designed to prevent backflow by allowing air into the system when a vacuum condition occurs. It operates under the principle of maintaining stable atmospheric pressure, which is fundamental for its function. When the system is at stable atmospheric pressure, the air inlet valve is closed, preventing any potential backflow from contaminated sources into the potable water supply. In contrast, positive pressure on the inlet side could lead to failure of the backflow prevention feature, as it does not address any backpressure conditions. Negative pressure at the outlet can create a vacuum, which the pressure vacuum breaker is designed to manage, but it does not tolerate it indefinitely without the risk of failure. Variable water temperatures can affect the operation and materials of the device, but they do not represent a defined hydraulic condition that it is designed to withstand without compromising its function. Therefore, the choice of stable atmospheric pressure reflects the hydraulic condition under which the pressure vacuum breaker can operate reliably without risk of failure.