Backflow Prevention

Backflow is the undesirable reversal of flow of a liquid, gas, or other substance in a potable water distribution piping system as a result of a cross-connection due to back-siphonage or back pressure.

Back-siphonage is the reversal of normal flow in a system caused by the negative pressure (vacuum or partial vacuum) in the supply piping.

Back-siphonage can be created when there is a stoppage of the water supply due to nearby fire-fighting, repairs or breaks in the city water mains, etc. The effect is similar to the sipping of an ice cream soda by inhaling through a straw which induces the flow in the opposite direction.

Back pressure backflow is the reversal of normal flow in a system due to an increase in the downstream pressure above that of the supply pressure.

Back pressure-backflow is created whenever the downstream pressure exceeds the supply pressure which is possible in installations such as heating systems, elevated tanks, and pressure producing systems. An example would be a hot water space-heating boiler operating at 15- 20 lbs pressure coincidental with the reduction of the city supply below such pressure (or higher in commercial boilers). As water tends to flow in the direction of least resistance, a back pressure- backflow condition would be created and the contaminated boiler water would flow back into the public drinking water supply.

A cross connection is a direct arrangement of piping line which allows the potable water supply to be connected to a line which contains a contaminant and/ or pollutant. An example is the common garden hose attached to a sill cock with the end of the hose lying in a cesspool. Other examples are a garden hose attached to a service sink with the end of the hose submerged in a tub full of detergent, supply lines connected to bottom-fed tanks, supply lines to boilers, supply lines to automatic irrigation systems.

The garden hose is the most common form of a cross connection. It can be easily connected to the potable water supply and used for a variety of potentially dangerous applications.

The purpose of a sill cock is to permit easy attachment of a hose for outside watering purposes. However, a garden hose can be extremely hazardous because they are left submerged in swimming pools, lay in elevated locations (above the sill cock) watering shrubs, chemical sprayers are attached to hoses for weed killing, etc.; and hoses are often left laying on the ground which may be contaminated with fertilizer, cesspools, and garden chemicals.

The purpose of a sill cock is to permit easy attachment of a hose for outside watering purposes. However a garden hose can be extremely hazardous because they are left submerged in swimming pools, lay in elevated locations (above the sill cock) watering shrubs, chemical sprayers are attached to hoses for weed killing, etc.; and hoses are often left laying on the ground which may be contaminated with fertilizer, cesspools, and garden chemicals.

A hose bibb vacuum breaker should be installed on every sill cock to isolate garden hose applications thus protecting the potable water supply from contamination.

Pollution of a water supply does not constitute as an actual health hazard, although the quality of the water is impaired with respect to taste, odor, and color. Contamination of a water supply, however, does constitute as a health hazard; the consumer being subjected to potentially lethal water borne disease or illness.

The degree of hazard is a commonly used phrase utilized in cross connection programs (backflow prevention programs) and is simply a determination of whether the substance in the non-potable water supply is toxic or non-toxic.

A toxic substance is any liquid, solid, or gas, which when introduced into a water supply creates, or may create, a danger to health and well-being of the consumer. An example is treated water boiler. A non-toxic substance is any substance that may cause a non-health hazard, is a nuisance or is aesthetically objectionable. For example, food stuff such as sugar, soda, etc.

1. Air Gap
2. Atmospheric Vacuum Breakers
3. Pressure Vacuum Breakers
4. Double Check Valve Assembly
5. Reduced Pressure Zone Backflow Preventers

A double check backflow prevention assembly may be used as protection of all direct connections through which foreign materials might enter the potable water system in concentration which would constitute a nuisance or aesthetically objectionable, such as air, steam, food, or other material which does not constitute a health hazard.

An RPZ may be used on all direct connections to the potable water supply which may be subject to back pressure or back-siphonage, and where there is the possibility of contamination by the material that constitutes as a potential health hazard.

Yes, OSHA requires that no cross connection be allowed in an installation unless it is properly protected with an approved backflow preventer. These requirements are covered in the B.O.C.A, Uniform Plumbing Code, and City, State, and Federal regulations.