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Terms used in articles on backflow testing.
Air Gaps– Physical separation between a potable water system and a receiving vessel or source of contamination. Air gap between the outlet of the potable system and the flood level rim of the receiving vessel or any source of contamination must be at least twice as large as the diameter of the potable water outlet and never smaller than 1 inch. May require additional pumping downstream of air gap. Safest and simplest means under backsiphonage and backpressure conditions. Useful for all hazard levels.
Atmospheric Vacuum Breaker-Consists of float check, check seat, air inlet port, and possibly a shutoff valve immediately upstream. Allows air to enter the downstream water connection to prevent backsiphonage. Used for backsiphonage conditions only.
Backflow – the flow of water or other liquids, mixtures or substances into the distributing pipes of the drinking water supply from any source.
Backpressure-Backflow that occurs when the pressure in an unprotected downstream piping system exceeds the pressure in the supply piping.
Backsiphonage – Resulting from negative pressures in the distributing pipes of a potable water supply.
Double Check Valve Devices– Consist of two independently acting, tightly closing, resilient seated check valves in series with test ports. Have tightly closing, resilient seated shutoff valves attached at each end of the assembly. Prevent backflow under backsiphonage and backpressure conditions.
Typically approved for only low to medium hazards.
Pressure Vacuum Breaker Devices– Consist of vacuum breakers with a loaded check valve and a loaded air inlet valve. Used for backsiphonage conditions only.
Reduced Pressure Zone Backflow Devices– Similar to the double check valve devices, but also contain an independently acting pressure relief valve between the two check valves (which sits lower than the first check valve). Protect against high water pollution hazards. Protect against backsiphonage and backpressure.
