Which statement accurately describes PVBs when backpressure is possible?

• A. PVBs are approved for both backsiphonage and backpressure.
• B. PVBs protect against backsiphonage and backpressure equally.
• C. PVBs can be used for health hazards if installed properly.
• D. PVBs protect against backsiphonage only, and are not approved if backpressure is possible.

Answer: (D)

The main idea is how a PVB functions in different backflow scenarios. A PVB is designed to prevent backsiphonage by venting to the atmosphere when supply pressure drops, stopping a siphon from pulling contaminants back into the potable supply. However, in a backpressure situation, downstream pressure can push water back toward the source, and a PVB is not built to withstand that reverse pressure. Because of this, PVBs are not approved for use when backpressure could occur. For systems where backpressure is possible (or where health hazards exist), other devices such as RPZs or double-check assemblies are used. So the statement that best fits is that PVBs protect against backsiphonage only and are not approved if backpressure is possible.