GLOSSARY & TERMS
Backflow Prevention
Backflow is the undesired reversal of flow of water and/or other substance into the potable water supply, via a cross-connection, due to a change in pressure caused by either Backpressure or Backsiphonage.
Backflow Prevention Assembly
A backflow prevention assembly or backflow preventer is a mechanical valve arrangement, which is designed to prevent the "backflow" or reversal of flow of water, once it has passed through the valve. There are different types of backflow preventers for different uses, and different degrees of hazard.
Because the backflow preventer is a mechanical device with springs, moving parts and rubber seating surfaces, which wear over time, it must be tested upon installation and every year thereafter to ensure that the assembly is working properly.
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Backsiphonage
Backsiphonage occurs when higher pressure fluids, gases, or suspended solids move to an area of lower pressure fluids.
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Cross-Connection Control
A cross-connection is an actual or potential link between the potable water supply (water safe for human consumption) and a non-potable source (any other type of liquid, gas or substance not fit for consumption and that can affect water quality). A cross-connection can be avoided by eliminating the link between the two sources. If the link cannot be removed, then the potable water supply must be protected through the use of a backflow prevention assembly.
TYPES OF BACKFLOW PREVENTERS
from Zurn
Atmospheric Vacuum Breaker (AVB)
An AVB is a device containing a float-check, a check seat, and an air inlet port. The flow of water into the body causes the float to rise and close the air inlet port. When the flow of water stops, the float falls and forms a check valve against backsiphonage and, at the same time, opens the air inlet port to allow air to enter and satisfy the vacuum. A shut-off valve immediately upstream may be an integral component of the assembly.
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An AVB can NOT be tested once it is installed.
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Double Check Valve Assembly (DC)
A DC is an assembly containing two independently acting approved check valves, four resilient-seated test cocks and two resilient-seated isolation valves.
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Pressure Vacuum Breaker (PVB)
A PVB is an assembly containing an independently acting, internally loaded check valve with an independently acting loaded air inlet valve, located on the discharge side of the check valve. A PVB shall have two resilient-seated isolation valves attached at each end of the assembly and two properly located resilient seated test cocks.
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Reduced Pressure Principle Assembly (RP)
A RP is an assembly containing two independently acting approved check valves together with a hydraulically operated, mechanically independent differential pressure relief valve located between the two check valves.
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