A check valve in an approved backflow assembly must be tight when?

A check valve in an approved backflow assembly must be tight when the assembly is subject to any backflow. This is crucial because the primary function of a check valve is to prevent the reverse flow of water, which can occur during backflow conditions. When backflow is present, there is a risk of contaminated water entering the clean water supply; hence, a tight check valve ensures that no contaminants can breach the system.

If the check valve does not seal properly during backflow, it can compromise the overall effectiveness of the backflow prevention assembly, allowing potentially harmful substances to mix with potable water. This adherence to maintaining a tight seal under backflow conditions is a fundamental aspect of backflow prevention design and operation, ensuring public health and safety by safeguarding drinking water systems.

In contrast, while the check valve may be closed or inoperative during maintenance or when the assembly is not in use, it is not required to be tight in those scenarios. The focus is exclusively on scenarios where backflow could occur.