Which backflow prevention device is typically used where higher protection is needed on cross-connections?

• A. Air gap
• B. Double-check valve
• C. Non-return valve
• D. Pressure-reducing valve

Answer: (B)

When protecting a water supply from backflow at a cross-connection, you want a device that reliably stops reverse flow while remaining practical for the job. A double-check valve assembly uses two check valves in series, creating redundancy so if one valve leaks, the other still blocks reverse flow. It can be tested to verify both valves seal properly, and it provides a higher level of protection than a single check valve without the complexity or cost of a reduced-pressure device. This makes it the typical choice when cross-connections require more protection than a simple valve can offer, yet a full high-hazard solution isn’t necessary. In contrast, an air gap offers very strong protection but isn’t a valve and isn’t always feasible in existing piping; a single non-return valve offers less protection, and a pressure-reducing valve does not by itself prevent backflow.