page_title: Atmospheric vacuum breaker
hierarchical_section_title: Atmospheric vacuum breaker
caption_attribution_description: English: If the pressure in the water system happens to drop, the poppet valve drops as well, to compensate for the loss of pressure, and so the hood is raised by the action of the poppet valve. Air is sucked into the pipe as well by the loss of pressure, and the vacuum is filled before back-siphonage can occur, because the pressure is neutralized by the air, which, in turn, creates a buffer between the system of potable water and the contaminated water. It must not be installed underground as well, but is seen raised above the ground, because its operation may suck in ground water, which may be contaminated as well, into the system.
context_page_description: An Atmospheric Vacuum Breaker is a backflow prevention device used in plumbing to prevent backflow of non-potable liquids into the drinking water system.
  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 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 pipes. AVBs must be installed a minimum of 6 inches above the highest usage point in the system 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.
context_section_description: An Atmospheric Vacuum Breaker (AVB) is a backflow prevention device used in plumbing to prevent backflow of non-potable liquids into the drinking water system. 
  
  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 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 pipes. 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.
caption: Diagram of Atmospheric Vacuum Breaker in both working states.
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