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Pressure
Pure water at sea level weighs 62.4 pounds per cubic foot. Thus, if the base of a cubic foot is divided into 144 one-inch squares, the weight of the column of water one foot...
Backsiphonage
Technically, if one siphons a fluid out of a container or a pipeline, one causes that fluid to flow up over the rim of the container or top of the pipe and then down into a lower elevation...
Airgap
An Air Gap is a physical separation of the supply pipe by at least two pipe diameters (never less than one inch) vertically above the overflow rim of the receiving vessel...