The term backflow means any unwanted flow of used or non-potable water or substance from any domestic, industrial or institutional piping system into the pure, potable water distribution system.

The direction of flow under these conditions is in the reverse direction from that intended by the system and normally assumed by the owner of the system.

Backflow may be caused by numerous specific conditions; but, basically the reverse pressure gradient may be due to either a loss of pressure in the supply main called backsiphonage, or by the flow from a customer's pressurized system through an unprotected cross-connection, which is called backpressure.

Thus the term backflow covers both a backsiphonage condition and a backpressure condition.

A reversal of flow in a distribution main-or in the customer's system-can be created by any change of system pressure wherein the pressure at the supply point becomes lower than the pressure at the point of use.

When this happens in an unprotected situation the water at the point of use will be siphoned back into the system; thus, potentially polluting or contaminating the remainder of the customer's system.

It is also possible that the contaminated or polluted water could continue to backflow into the public distribution system.

The point at which it is possible for a non-potable substance to come in contact with the potable drinking water system is called a cross-connection.

To prevent backflow from occurring at the point of a cross-connection a backflow prevention assembly must be installed. However, it is important the backflow prevention assembly match the particular hydraulic conditions at that location and is suitable to protect against the degree of hazard present.

The particular type of backflow preventer appropriate for specific needs will be discussed later. First, it is necessary to understand some basic hydraulics which govern the principles of backflow and cross-connection control.

The type of backflow preventer used to prevent backflow from occurring at the point of a cross-connection depends on the type of substance which may flow into the potable water supply. A pollutant is considered to be any substance which would affect the color or odor of the water, but would not pose a health hazard.

This is also considered a non-health hazard.

A substance is considered a health hazard if it causes illness or death if ingested. This health hazard is called a contaminant.

Sewage and radioactive materials are considered Lethal Hazards. This is because of the epidemic possibilities associated with sewage and the tremendous dangers associated with radioactive material.

Therefore, we must install backflow prevention device at the cross-connection points. The following requirements shall apply: 

A. Backsiphonage, Non-Continuous Pressure, Non-Health Hazard
1. Atmospheric vacuum breaker-ASSE 1001(AVB)
2. Hose connection vacuum breaker-ASSE 1011

3. Any backflow protection device approved for protection against backsiphonage with non-continuous or continuous pressure

and a Non-Health Hazard or Health Hazard.

B.Backsiphonage, Continuous Pressure, Non-Health Hazard

1. Pressure vacuum breaker-ASSE 1020(PVB)
2. Spill-resistant vacuum breaker-ASSE 1056(SVB)
3. Backflow preventer with intermediate atmospheric port-ASSE 1012

4. Double check valve assembly-ASSE 1015(DC and DCDA)

5. Any backflow protection device approved for protection against backsiphonage with continuous pressure and a Non-Health Hazard or Health Hazard.

C. Backsiphonage, Non-Continuous Pressure, Health Hazard
1. Atmospheric vacuum breaker-ASSE 1020(PVB)
2. Hose connection backflow preventer-ASSE 1052
3. Any backflow protection device approved for protection against backsiphonage with non-continuous or continuous pressure and a Health Hazard.

D. Backsiphonage, Continuous Pressure, Health Hazard
1. Pressure vacuum breaker-ASSE 1001(AVB)
2. Spill-resistant vacuum breaker-ASSE 1056(SVB)
3. Reduced pressure backflow preventer assemblies-ASSE 1013(RP, RPZ and RPBA)

4. Any backflow protection device approved for protection against backsiphonage with continuous pressure and a Health Hazard.

E. Back Pressure, Non-Health Hazard
1. Double check backflow preventer -ASSE 1024(DuCh)

2. Double check valve assembly-ASSE 1015(DC and DCDA)

3. Reduced pressure backflow preventer assemblies-ASSE 1013(RP, RPZ and RPBA)

F. Back Pressure, Health Hazard

1. Reduced pressure backflow preventer assemblies-ASSE 1013(RP, RPZ and RPBA)

by Young Ho Kim, President

C&T Corporation