Resources: Backflow Definitions

• Backflow: the flow of any foreign liquids, gases, or substances into the distributing pipe lines of a potable supply of water. Backflow may occur under two conditions--pressure greater than atmospheric, and pressure that is subatmospheric.
   
• Back Pressure: backflow caused by a pump, elevated tank, boiler, or other means that could create pressure within the system greater than the supply pressure.
   
• Back Siphonage: a form of backflow due to a negative or subatmospheric pressure within a water system.
   
• Cross Connection: any connection or structural arrangement between a public or a consumer's potable-water system and any nonpotable source or system through which backflow can occur. (Bypass arrangements, jumper connections, removable sections, swivel or change-over devices, and other temporary or permanent devices through which, or because of which, backflow can occur are considered to be cross connections.)
   
• Double Check Assemblies: Protects the potable water supply from a pollutant caused by a cross connection. Only used in a backpressure condition. Consists of two independently operating check valves, two shut off valves, and four test cocks. Used in low hazard conditions.
   
• Double Check Detector Check Assembly: Protects potable water systems from a pollutant caused by a cross connection on a fire system and also detects any unauthorized use of water and leaks on the fire line system. Only used on a backpressure condition. Consists of two independently operating check valves, two shut off valves, and bypass assembly with meter. Used in low hazard conditions.
   
• Reduced Pressure Principle Backflow Prevention Assembly: Protects the potable water supply from contamination caused by a cross connection. May be used on a back siphonage and back pressure condition. Consists of two independently operating check valves, a hydraulically operated mechanical pressure differential relief valve located between the check valves and below the first check, two shut off valves, and appropriate test checks. Used in high hazard conditions.
   
• Reduced Pressure Detector Assembly: Protects the potable water supply from contamination caused by a cross connection on a fire system and also detects any unauthorized use of water and leaks on a fire line water system. May be used on a back siphonage and backpressure condition. Consists of two independently operating check valves, a hydraulically operated mechanical pressure differential relief valve located between the check valves and below the first check, two shut off valves, bypass assembly with small diameter RP and meter, and appropriate test checks. Used in high hazard conditions.

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