An Atmospheric Vacuum Breaker (AVB) is a

backflow prevention device A backflow prevention device is used to protect potable water supplies from contamination or pollution due to backflow. In water distribution systems, water is normally maintained at a significant pressure to enable water to flow from the tap, ...

used in

plumbing Plumbing is any system that conveys fluids for a wide range of applications. Plumbing uses piping, pipes, valves, piping and plumbing fitting, plumbing fixtures, Storage tank, tanks, and other apparatuses to convey fluids. HVAC, Heating and co ...

to prevent

backflow Backflow is a term in plumbing for an unwanted flow of water in the reverse direction. It can be a serious health risk for the contamination of potable water supplies with foul water. In the most obvious case, a toilet flush cistern and its wate ...

of non-potable

liquid Liquid is a state of matter with a definite volume but no fixed shape. Liquids adapt to the shape of their container and are nearly incompressible, maintaining their volume even under pressure. The density of a liquid is usually close to th ...

s into the

drinking water Drinking water or potable water is water that is safe for ingestion, either when drunk directly in liquid form or consumed indirectly through food preparation. It is often (but not always) supplied through taps, in which case it is also calle ...

system. It is usually constructed of

brass Brass is an alloy of copper and zinc, in proportions which can be varied to achieve different colours and mechanical, electrical, acoustic and chemical properties, but copper typically has the larger proportion, generally copper and zinc. I ...

and resembles a 90-degree elbow with a hood on its top to allow

air An atmosphere () is a layer of gases that envelop an astronomical object, held in place by the gravity of the object. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A stellar atmosph ...

to enter the water system if a

siphon A siphon (; also spelled syphon) is any of a wide variety of devices that involve the flow of liquids through tubes. In a narrower sense, the word refers particularly to a tube in an inverted "U" shape, which causes a liquid to flow upward, abo ...

attempts to form. Inside this elbow is a

poppet valve A poppet valve (also sometimes called mushroom valve) is a valve typically used to control the timing and quantity of petrol (gas) or vapour flow into or out of an engine, but with many other applications. It consists of a hole or open-ended ch ...

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. These devices, since they work on atmospheric principles, cannot be installed in an enclosure containing air contaminants. Those contaminants could be drawn into the device, thus fouling the

pipe Pipe(s), PIPE(S) or piping may refer to: Objects * Pipe (fluid conveyance), a hollow cylinder following certain dimension rules ** Piping, the use of pipes in industry * Smoking pipe ** Tobacco pipe * Half-pipe and quarter pipe, semi-circular ...

s. AVBs must be installed a minimum of 6 inches above the highest usage point in the system (i.e. sprinkler, drip emitter, etc.) Underground installation of AVBs is ''entirely ineffectual'' in providing backflow protection as groundwater in the underground vault could be drawn into the water system, contaminating it. The AVB can be used in high hazard situations but not with continuous pressure, as the poppet would likely stick and the AVB would no longer function properly. A shutoff valve should never be placed downstream of any AVB, as this would result in continuous pressure on the AVB. The AVB is not a testable device. Rohrbeluefter_E.0127.jpg, Atmospheric vacuum breaker with a

tundish The word tundish originates from a shallow wooden dish with an outlet channel, fitting into the bunghole of a tun or cask and forming a kind of funnel for filling it. These were originally used in brewing. In general, any tundish will accept flo ...

Rohrbelüfter_E.png, Functional schematic (labelled in German) AVB-1.JPG, One-Inch Brass Atmospheric Vacuum Breaker mounted on PVC Pipe

References

{{DEFAULTSORT:Atmospheric Vacuum Breaker Plumbing valves Irrigation Backflow

See also

References