Backflow Devices: Installation & Testing

Backflow can be a serious health risk

Backflow is a plumbing term for when water flows in the incorrect direction. This can occur when the private property water supply is lost or is at a low pressure due to utility company service repairs.

Backflow is the undesirable reversal of flow of a liquid, gas, or suspended solid into the potable water supply. In other words, its a term in plumbing for an unwanted flow of water in the reverse direction. By using a backflow preventer ensures that this does not happen. When potable water system connect with a non-potable water system we have what is called cross connections.  These connections must be carefully designed and installed to prevent backflow.

Backflow Prevention Devices

The simplest, most reliable way to provide backflow prevention is to provide an air gap. An air gap is simply an open vertical space between any device that connects to a plumbing system (like a valve or faucet) and any place where contaminated water can collect or pool. A simple air gap has no moving parts, other than flowing water. Other preventive devices include but not limited to

  • Air gap
  • Atmospheric vacuum breaker (AVB)
  • Chemigation valve (primarily used in agriculture)
  • Double check valve, or double check valve assembly (DCVA)
  • Pressure vacuum breaker assembly (PVB)
  • Reduced pressure zone device (RPZ)
  • Spill resistant pressure vacuum breaker assembly (SPVB)
  • Vacuum breaker

Regulatory Requirements

To prevent contamination due to back pressure, many health regulatory regimes require an air gap or mechanical backflow prevention assembly between the delivery point of mains water and local storage or use. Where submerged mains inflow is permitted,a backflow prevention assembly is required, which protects the potable water system from contamination hazards. A check valve is a basic form of backflow prevention, but often more complex devices are required because check valves are not considered to be reliable, when compared to more sophisticated devices with redundancies and reduced-pressure zones.

In many countries. approved backflow prevention assemblies are required by law, and must be installed in accordance with plumbing or building codes.A typical backflowassembly has test cocks and shut-off valves, and must be tested when installed, if relocated or repaired, and also on a periodic basis

Risk of contamination

The precise measures required to prevent backflow depend on the risk of contamination, i.e. the condition of the water in the connected system. This is categorized into different risk levels:

  • Category 1: No risk. Potable water
  • Category 2: Aesthetic quality affected, e.g. water which may have been heated
  • Category 3: Slight hazard from substances of low toxicity, e.g. cold water storage tanks
  • Category 4: Significant hazard, e.g. pesticides
  • Category 5: Serious health risk, e.g. human waste

How Alcom Plumbing can Help

Only licensed plumbers with backflow prevention accreditation issued by a registered training organisation (backflow plumbers) can inspect, commission and test backflow devices. With that said, Alcom Plumbing are accredited in backflow prevention and works with Sydney Water to ensure compliance.