Types of Backflow

Backsiphonage is the reversal of normal flow resulting from negative or sub-atmospheric pressure in piping system. A partial vacuum is created within the piping system. Backsiphonage result in fluid flow in an undesirable or reverse direction. It is caused by atmospheric pressure exerted on a pollutant liquid forcing it towards a potable water supply system that is under a vacuum. Negative pressure is a very powerful force and is some cases very damaging. Negative pressure can cause a water transmission mains or water storage tanks to collapse.

Backpressure is the reversals of normal flow resulting from an increase of pressure downstream of the incoming public water system or within the non-potable piping system.  Backpressure occurs if there is a decrease in the public water system distribution system pressure that is lower than the non-potable system pressure or an increase in the non-potable water system pressure that is greater than the potable water system pressure.  Downstream pressure in the piping system that is greater than the incoming pressure in the piping system is backpressure backflow.