Which device uses two independent check valves with an automatic differential valve between them to prevent backflow?

Which device uses two independent check valves with an automatic differential valve between them to prevent backflow?

• A. Air Gap
• B. Reduced Pressure Principal Device
• C. Atmospheric Vacuum Breaker
• D. Backflow

Answer: (B)

Backflow prevention devices protect the potable water supply from contamination by irrigation water or pesticides. The described arrangement—two independent check valves with a differential valve placed between them that vents to drain automatically—fits the reduced pressure principle backflow preventer. If pressure on the downstream side drops or a check valve leaks, the differential valve opens and water is released to the drain, keeping downstream pressure lower and preventing any contaminated water from flowing back into the supply. This provides strong protection against both backflow and back-siphonage, which is why it’s chosen as the correct device. An air gap is just a physical separation with no internal valves, an atmospheric vacuum breaker relies on venting to the atmosphere and doesn’t offer the same level of protection, and “backflow” isn’t a device.

Backflow prevention devices protect the potable water supply from contamination by irrigation water or pesticides. The described arrangement—two independent check valves with a differential valve placed between them that vents to drain automatically—fits the reduced pressure principle backflow preventer. If pressure on the downstream side drops or a check valve leaks, the differential valve opens and water is released to the drain, keeping downstream pressure lower and preventing any contaminated water from flowing back into the supply. This provides strong protection against both backflow and back-siphonage, which is why it’s chosen as the correct device. An air gap is just a physical separation with no internal valves, an atmospheric vacuum breaker relies on venting to the atmosphere and doesn’t offer the same level of protection, and “backflow” isn’t a device.