Backflow Prevention Practice Exam

What will occur if there is a supply pressure loss with a functional check valve in a pressure vacuum breaker?

1. Admit air into the downstream piping

2. Be subject to backpressure

3. Discharge water

4. Retain water pressure downstream of the check valve

The correct answer is: Retain water pressure downstream of the check valve

When a functional check valve is present in a pressure vacuum breaker, a supply pressure loss will lead to the retention of water pressure downstream of the check valve. This is because the check valve is designed to prevent reverse flow and allows water to stay in the downstream piping as long as it is functioning properly. As long as the system maintains a pressure higher than the atmospheric pressure and the check valve remains intact, it will hold the water pressure upstream of it, effectively isolating the downstream piping from the effects of the supply pressure loss. The other options do not align with how a check valve operates. For instance, if the check valve were to fail or allow backflow, only then would air potential could be admitted into the downstream piping, leading to the opposite scenario than what's invoked here. Moreover, while backpressure pertains to situations involving pressure differentials that could occur in other types of systems, a supply pressure loss specifically leads to water retention if the check valve remains operational.