Typical Backflow Assemblies

Backflow prevention assemblies can reduce or eliminate backflows by segregating drinking and non-potable water piping. This is done either by providing an air gap or by installing a backflow prevention assembly (BPA) between the two plumbing systems.


It is important that the backflow prevention assembly match the location’s particular hydraulic conditions and is suitable to protect against the degree of hazard present. Any BPA installed must be a design approved and listed by University of Southern California Foundation for Cross Connection Control and Hydraulic Research. Also, the BPA must be installed according to the most recent plumbing code adopted by the City of Garland.

Testing & Maintenance

Once installed, these BPA are subject to initial and periodic testing and maintenance requirements to confirm their continued operational effectiveness. Such testing must be performed by a state licensed Backflow Tester (PDF) registered with the City of Garland.

Assembly Examples

  1. Air Gap
  2. Double Check Detector
  3. Double Check Valve
  4. Hose Bibb Vacuum Breaker
  5. Pressure Vacuum Breaker
  6. Reduced Pressure Detector
  7. Reduced Pressure Zone

Air Gap Assembly ExampleThere is a vertical, physical separation between the end of a water supply outlet and the flood-level rim of a receiving vessel.

Separation must be at least twice the diameter of the water supply outlet and never less than one inch.

It is effective against back pressure backflow and back-siphonage and may be used to isolate health or non-health hazards.