Monday, October 3, 2011

Backflow Prevention

  Back-flow is the reversal of the normal and intended direction of water flow in a water system. Devices and assemblies known as back-flow preventers are installed to prevent back-flow, which can contaminate potable water supplies.

Why is back-flow a problem?
  Back-flow is a potential problem in a water system because it can spread contaminated water back through a distribution system. For example, back-flow at uncontrolled cross connections (cross-connections are any actual or potential connection between the public water supply and a source of contamination or pollution) can allow pollutants or contaminants to enter the potable water system. Sickness can result from ingesting water that has been contaminated due to back-flow.

Backflow may occur under the following two conditions:

back-pressure: Back-pressure is the reverse from normal flow direction within a piping system as the result of the downstream pressure being higher than the supply pressure. This reduction in supply pressure occurs whenever the amount of water being used exceeds the amount of water being supplied (such as during water-line flushing, fire-fighting, or breaks in water mains).

back-siphonage: Back-siphonage is the reverse from normal flow direction within a piping system that is caused by negative pressure in the supply piping (i.e., the reversal of normal flow in a system caused by a vacuum or partial vacuum within the water supply piping). Back-siphonage can occur when there is a high velocity in a pipe line, when there is a line repair or break that is lower than a service point, or when there is lowered main pressure due to high-water withdrawal rate (such as during fire-fighting or water-main flushing)
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1 comment:

  1. I really needed this kind of useful information. Very informative and fantastic article and very clearly explained.
    Great Job!
    Scarborough Home Inspector