Which device is used to prevent backflow in piping systems?

• A. Pressure gauge
• B. Backflow preventer
• C. Ammonia vapors near connections
• D. Misting water

Answer: (B)

Preventing backflow is about keeping fluid moving in one direction so contaminants from downstream can’t be drawn back into the clean supply. The device used to achieve this is the backflow preventer. It is designed to block reverse flow, protecting the water supply by responding to pressure changes that could cause siphoning or backflow. Depending on the system, backflow prevention can involve different mechanisms, such as checks, relief valves, or air gaps, but the common purpose is to stop any reverse movement of water.

A pressure gauge, by contrast, only measures pressure and doesn’t stop backflow. Ammonia vapors near connections describe a hazard or leak condition, not a prevention device. Misting water isn’t a backflow control mechanism either.