Water Conditioning & Purification Magazine

Air gap

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A clear vertical space through the free atmosphere between the lowest opening of any pipe or faucet conveying water or waste to a tank, plumbing fixture receptor, or other device and the flood level rim of the receptacle. An air gap prevents cross connection between a water treatment device and a possible source of wastewater, so as to prevent a reverse flow of water from the sewer into the water supply system. Otherwise, a reverse flow could occur when negative pressure is created in the water supply line, or from an increase in the pressure in the sewer system. Local plumbing codes usually require the air gap to be twice the diameter of the inlet, with a minimum width of 1.5 inches.

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