Methods Used to Prevent Backflow 1

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The methods used to control backflow can be separated into two categories, non-mechanical and mechanical. The non-mechanical backflow control method would be arranging the piping to eliminate the possibility of backflow or the cross-connection. The mechanical method would be the installation of backflow prevention devices or assemblies. A specific arrangement or configuration of the plumbing system or the use of mechanical devices or device assemblies can effectively prevent backflow provide that the method used is correct for the intended purpose and installed according to the manufacture specifications.

The mechanical backflow control method can be separated into two categories, devices, and device assemblies. Backflow prevention devices for the most part do not have upstream or downstream shut-off valves or test cocks. Typically, they cannot be tested or repaired inline. Backflow prevention device assemblies are equipped with upstream and downstream shut-off valves. Backflow prevention device assemblies are equipped with test cocks located upstream and downstream side of the check valves. They can be tested and repaired inline. Some backflow prevention devices and assemblies can only be used to prevent backsiphonage while other can be used to prevent backsiphonage and backpressure.

The methods used to prevent backflow are as follows:

  • Air Gap – ASME A112.1.3
  • Double Check Valve Assemblies – ASSE 1015
  • Reduced Pressure Principle Assemblies – ASSE 1013
  • Pressure Vacuum Breakers – ASSE 1020
  • Spill-Resistant Vacuum Breakers – ASSE 1056
  • Atmospheric Type Vacuum Breakers – ASSE 1001
  • Dual Check Valve with Intermediate Atmospheric Vent ASSE 1012
  • Dual Check Valve ASSE 1024
  • Carbonated Beverage Backflow Preventers ASSE 1022
  • Hose Connection Vacuum Breakers Backflow Preventers ASSE 1011
  • Hose Connection Dual Check Valve with Atmospheric Vent ASSE 1052
  • Laboratory Faucet Dual Check Backflow Preventers ASSE 1035
  • Barometric Loop

Piping arrangements such as an Air Gap should be the considered first when attempting to eliminate or control the cross-connection. When the cross-connection cannot be eliminated or controlled by non-mechanical means, mechanical backflow prevention device/assemblies should be used.

The selection of the method to control backflow is based upon the degree of hazard posed by the cross-connection, the resultant force associated with the cross-connection, the type of cross-connection and in some case the public water system cross-connection program plan of action.