Backflow Prevention - Evermist Ltd


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What is backflow?

Backflow happens when water in an irrigation system flows back into the water supply. Backflow allows contaminants such as fertilizers, pesticides or animal residues to flow back into the drinking water.

While irrigation systems might begin with potable water, they can be contaminated by submerged sprinklers, auxiliary water supplies, ponds, reservoirs, swimming pools or other sources of nonpotable water.
What causes backflow?

Backflow is caused by backpressure or backsiphonage. Backpressure is the flow from a pressurized system through an unprotected cross-connection into the potable water supply. This occurs when a higher pressure is generated in the irrigation system by a pump or by elevation differences.

The primary causes of backpressure are:

Booster pump designed without backflow prevention devices.

Interconnection with another system operated at a high pressure, like a fertilizer injector system.

Changes in system pressure which cause the pressure at the supply point to become lower than the pressure point of use which allows the nonpotable water to be backsiphoned into the main supply line.

The primary causes of back-siphonage are:

Undersized piping.

Line repairs or breaks that are lower than a service point.

Lower main pressure from high water-withdrawal rates.

Reduced supply main pressure on suction side of a booster pump.

Connections between the water supply and a source of contamination are called cross-connections.

For any irrigation system, an approved backflow prevention device must be installed at the cross-connection point to prevent backflow. The backflow prevention apparatus must match specific hydraulic conditions at the site and be capable of protecting aainst the degree of hazard present.