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.
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.
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.