Backflow Prevention Practice Exam

The air-inlet valve of an atmospheric vacuum breaker is held closed by which force?

1. Atmospheric pressure

2. Cotter pins

3. Gravity

4. Water pressure

The correct answer is: Water pressure

In the context of an atmospheric vacuum breaker, the air-inlet valve plays a crucial role in maintaining proper hydraulic conditions within a plumbing system. The force that holds the air-inlet valve closed is primarily water pressure. When water flows through the atmospheric vacuum breaker, the pressure of the water causes the air-inlet valve to remain closed, thus creating a barrier that prevents backflow and potential contamination of the potable water supply. This is essential in avoiding situations where negative pressure could draw contaminants from the atmosphere into the water supply. It's also important to understand that the operation of the air-inlet valve is designed to be a safety feature. If the water pressure drops significantly—such as in the event of a system failure or when a faucet is opened—this loss of pressure will allow the air-inlet valve to open, which then helps to prevent a vacuum condition that could lead to backflow. The other choices, while related to various mechanical or environmental forces, do not accurately describe the mechanism by which the air-inlet valve is held closed in the context of an atmospheric vacuum breaker. Atmospheric pressure and gravity do play roles in many situations within plumbing systems, but in this particular case, it is the water pressure that is the defining factor.