Protecting against backflow in process lines

Backflow—a flow-reversal, by which liquids get into places they do not belong—can be serious. Here is how to prevent it. 

I I Backflow is most simply defined as a reversal of the normal direction of flow of piped liquids. It happens when, for one reason or another, upstream pressure falls below downstream pressure. Backflow can result from a pump failure, heavy upstream drawoff, downstream pressure rise, ruptured lines and many other conditions. 

What makes backflow a major cause of concern is that reverse flow of liquids often has highly undesirable consequences. In mixing tanks, for example, backflow of mixed product to feedstock holding-tanks can result in contamination and costly waste. Backflow can also create hazardous conditions, particularly where toxic or explosive fluids are involved. 

Backflow presents its most serious problems, of course, when human health may be affected. For example, where a single water-supply system furnishes both potable water and process water, great care must be taken to protect potable water from possible contamina- 

Barometric loop provides protection against backsiphonage but not backpressure 

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