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A double check valve or double check assembly (DCA) is a backflow prevention device designed to protect water supplies from contamination. [1] It is different from the two-way check valves (sometimes erroneously referred to as double check valves) used in air brake systems on heavy trucks which select from the highest pressure source.
Check valve (usually not a legally approved method of backflow prevention.) Chemigation valve (primarily used in agriculture) Double check valve assembly (DCVA) Dual check valve (A dual check is not a testable device and is mainly used on residential customers) Pressure vacuum breaker assembly (PVB) Reduced pressure zone device (RPZ)
This gauge uses hoses attached to the various test cocks of the RPZD and checks to be certain that the check valve springs as well as the relief valve spring are not fouled and are working properly. There is a variety of manufacturers of these gauges, but most utilize either a three-valve or a five-valve design to test the RPZD in different ways.
Regulations for these check valves specify the design capabilities of the valve used, according to the hazard. Category 2 contamination may be prevented by a single check valve, but category 3 requires a double check valve (these are manufactured as a convenient single unit, or even integrated into tap (faucet) fittings). Category 5 requires an ...
Inside this elbow is a poppet valve that is held "up" by the water pressure found in the system, closing the air entrance to the device. If the pressure in the "upstream side" is reduced to atmospheric pressure or below, the poppet valve drops and allows air to enter the system, breaking the siphon. [1]
Water cannot flow from the sink to the tap in normal circumstances, even if the water supply loses pressure. An air gap, as related to the plumbing trade, is the unobstructed vertical space between the water outlet and the flood level of a fixture. [1]
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