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Where submerged mains inflow is permitted, [further explanation needed] a backflow prevention assembly is required, which protects the potable water system from contamination hazards. A check valve is a basic form of backflow prevention, but often more complex devices are required because check valves are not considered to be reliable, when ...
Backflow occurs for one of two reasons, either back pressure or back siphonage. [1] Back pressure is the result of a higher pressure in the system than in its supply, i.e. the system pressure has been increased by some means. This may occur in unvented heating systems, where thermal expansion increases the pressure.
Because certain combinations of check valve failure and/or system backpressure cause the relief valve to discharge, the device must be mounted in a location where the drain will not become flooded. An example of where backflow would harm the water supply is the use of well washing devices inside underground sewerage pumping stations.
It is usually constructed of brass and resembles a 90-degree elbow with a hood on its top to allow air to enter the water system if a siphon attempts to form. 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 ...
A pressure vacuum breaker (PVB) is a type of backflow prevention device, used to keep non-potable (or contaminated) water from entering the water supply. A PVB is similar to an atmospheric vacuum breaker (AVB), except that the PVB contains a spring-loaded poppet. This makes it acceptable for applications that are high hazard or where valves are ...
"My personal opinion is that our water system was not compromised, but the law says that doesn't matter," Majich said. "If you lose a house, you do the testing, so we're waiting for the results."
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