Principles of Backflow Prevention

1   2   3   4   5   6   7   8   9   10   11  

Protecting and maintaining water quality is one of the most important aspects facing us today. since we cannot increase our supply of water, we must insure measures are in place to keep it safe. Fortunately, there is a simple solution to protecting the quality of this valuable resource. Understanding the health risks of cross-connection and backflow, and the solutions available, is paramount to insuring a continued source of potable water.

What Is Backflow?

Backflow is the undesirable reversal of flow of water or mixture of water and other liquids, gases, or other substances into the distribution pipes of the potable supply of water from any source or sources.

When Does Backflow Occur?

Backflow may be caused by conditions of gravity, vacuum or other pressure changes. There are two factors that contribute to reversal of flow in pipelines. One is back-siphonage and the other is backpressure.

Back-siphonage condition exists when there is negative or sub-atmospheric pressure in the supply piping, allowing downstream substances to be siphoned into the potable water supply. Under-sized pipes, pipeline breaks, and high withdrawl rates can create vacuums, which contribute to the occurrence of back-siphonage.

Top of Page

Backpressure condition exists when a pressure higher than the supply is created in the downstream piping, allowing downstream substances to be pushed into the potable water supply. Backpressure can occur when higher pressures downstream are generated by pumps, thermal expansion, and elevation.

What Is a Cross-Connection?

The term Cross-Connection refers to any unprotected actual or potential connection or structural arrangement between a public or a consumer's potable water system and any other source or system through which it is possible to introduce into any part of the potable water system and any used water, industrial fluid, gas or substances other than the intended potable water with which the system is supplied.

By-pass arrangement, jumper connections, removable sections, swivel or change-over devices and other temporary or permanent devices through which or because of which backflow can or may occur are considered to be cross-connections.

Top of Page

The Solution Is Clear

It is evident that we cannot eliminate either the occurrence of backflow nor can we prevent cross-connectionsfrom being created. We must therefore provide a means of protecting drinking water systems from the hazards of backflow occurrences throuh cross-connections.

Mechanical backflow prevention devices and assemblies offer the best protection against cross-connection hazards. Backflow prevention devices prevent backflow by stopping the reversal of flow, but are not testable once installed because they do not have inlet and outlet shut-off valves or test cocks. Backflow prevention assemblies include an inlet and outlet shut-off valve and test cocks to facilitate testing of the assembly while it is in its functional in-line position. Furthermore, backflow preventers may be installed at the source of potential contamination or on the water service line itself.

Standards, Approvals, and Listings

Approval agencies, representing many diverse geographical areas and levels of government have established performance criteria regarding the function, manufacturing, installation, testing, and maintenance of backflow prevention devices and assemblies. The overall objective of the preformance criteria is to insure the sanctity of drinking water; however, each standard specifies different requirements relating to mechanical function, material requirements and testing for backflow preventers.

It is the task of backflow prevention manufacturers to produce a single product within a product category that complies with all applicable standards and the acceptance of such products are driven by the state, county and even the local city.

1   2   3   4   5   6   7   8   9   10   11  

Top of Page

Text courtesy of Wilkins a Zurn company.