本powerpoint演示文稿首先介绍防止回流的六种基本方法，包括: 气隙； 大气真空断路器； 压力真空断路器； 防溢压力真空断路器； 双止回阀总成；和 减压原理组件。介绍了选择防回流阀的注意事项，包括水力、组件尺寸过大、足够的流量和压力、热膨胀、危险类型， 保护手段，以及 安装要求。包括数字。

This powerpoint presentation begins by presenting six basic means of protection from backflow, including: Air Gap; Atmospheric Vacuum Breaker; Pressure Vacuum Breaker; Spill Resistant Pressure Vacuum Breaker; Double Check Valve Assembly; and, Reduced Pressure Principle Assembly. Considerations for selecting a backflow preventer are presented, including hydraulics, over sizing of assemblies, adequate flow and pressure, thermal expansion, types of hazards, means of protection, and installation requirements. Includes figures.