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Backflow Assemblies & Methods

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Types of Backflow Assemblies


1. Reduced Pressure Principle Assembly (RP)

Used on health hazards in buildings and is a combination of check valves and an air inlet allowing water from the private system to vent when City pressure drops.


  • 1 foot above the floor
  • No higher than 5 feet
  • Adequate drain
  • Adequate protection from vandalism if outdoors
  • Protect from freezing


2. Pressure Vacuum Breaker (PVB)

Mainly used for irrigation. It has a one way check and a spring loaded air inlet valve that closes when City water main pressure drops.


  • No backpressure
  • 12" above high point of use
  • Adequate protection from vandalism if outdoors
  • Protect from freezing


3. Double Check Valve Assembly (DCVA)

Typically used on non-health hazards in buildings and on fire lines. It uses two spring loaded valves.


  • 12" above the floor
  • No higher than 5 feet
  • Protect from freezing

4. Atmospheric Vacuum Breaker (AVB)


Used mainly on irrigation systems. It has an air inlet valve that will drop to draw in air thus preventing sprinkler system water from entering the City's water mains.


  • Not under continuous pressure for more than 12 hours
  • No downstream valves
  • No backpressure
  • Six inches above high point of use
  • Protect from freezing

Types of Backflow Methods

1. Air Gap

Used mainly on tanks and faucets, it is a gap between the pipe and the container.


  • The gap needs to be a minimum 2 times the supply pipe diameter
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