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Backflow
In plumbing systems, fluids move in one direction from areas of high pressure to areas of low pressure. Municipal water distributors send clean water at high pressure. Open faucets at homes and offices produce low-pressure release. This establishes the flow of water in one direction from municipal water sources to local buildings. Heavy demands on main water supplies may create pressure imbalances that reverse the flow of water. The term "backflow" describes the reversal of water direction. If a faucet is connected to a contaminating source, harmful particles can backflow into the fresh water supply. Backflow preventors are used to prevent water contamination.
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Back-Siphonage
Recognized as the most common type of backflow, back-siphonage is brought about by a negative pressure (vacuum) in a potable water system. Back-siphonage can occur when a water main breaks or firefighting operations place sudden heavy demand on the main water supply – consequently lowering water pressure significantly. A sudden drop in water pressure can back siphon wastewater flowing into the potable water supply entering local buildings. Backpressure is another type of backflow that occurs when the downstream pressure is higher than the supply pressure.
Cross-Connection
A cross connection is any connection between potable and non potable water sources. Residential cross connections occur when garden hoses are used to spray herbicides or insecticides on lawns or to flush out sewer pipe clogs. A sudden drop in water pressure of mains causes harmful contents in the hose to backflow and contaminate the drinking water supply of the home.
Backflow Prevention
State agencies (Health Depts, State Environmental Protection Agency [EPA], State Department of Environmental Quality [DEQ], etc) hold municipal water distributors accountable for potable water systems by installing and maintaining backflow devices on all cross connection points. While backflow preventors protect municipal water supply from contamination, backflows can still occur in the home. The simplest means of providing backflow prevention in the home is the physical separation, known as an air gap, of a water supply outlet and the receiving plumbing fixture. The following mechanical backflow prevention devices provide physical barriers to backflows in individual plumbing systems:
- Reduced-pressure principle assembly
- Pressure vacuum breaker assembly
- Double check valve assembly
Licensed plumbers periodically inspect backflow preventors for functioning order. Backflow testing is performed with properly calibrated gauge equipment.
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