back siphonage

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back siphonage

A reversal of the normal flow of water or other liquid due to a negative-pressure gradient. Back siphonage in a water system may result in contamination, triggering a “boil order” (i.e., an order to boil water before drinking so as to kill potential contaminants).

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* When hydrostatic pressure inside the pipe is lower than pressure outside the pipe (i.e., atmospheric pressure), back siphonage occurs and vacuum breakers are appropriate backflow prevention devices.

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The RPZ design features triple security to provide optimum protection against back pressure and back siphonage: two check valves and a discharge valve divide the unit into three chambers, each providing a separate pressure zone.

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If the consumer has a private water supply or even reuses some of the city water for other purposes, definite precautions should be taken to prevent any possible back siphonage induced by opening a large valve on a lower floor, especially when the city line has low pressure, thus allowing a submerged inlet or hose on an upper level to siphon polluted water into the lines.