4 Common Types of Backflow Prevent Devices

Similar to heart valves in the human heart, backflow devices allow water to flow through one way and close when there is pressure coming back through. They are critical tools for blocking contaminated water from entering our clean water systems in Calgary.

Backflow prevention devices are also used in public sectors such as municipal water systems, food processing plants, medical and dental water supplies, and many industrial applications throughout Calgary.

What types of backflow testing devices are available in Calgary?

There are four basic designs, but they’re not all created equal. Here is a breakdown of the most common ones.

1. Atmospheric vacuum breakers (AVB)

AVBs are the least expensive, but they are also least reliable and least recommended. They cannot be used where subject to continuous pressure for more than 12 hours at a time or where shutoff valves would be located downstream, or where there is a potential for backpressure.


  • Six inches or more above the highest outlet in the zone
  • Vertical, with the bonnet on top (prevents back-siphonage only)
  • Installed downstream from zone control valves, one unit per zone
  • No chemigation

2. Pressure vacuum breaker assemblies (PVB)

PVBs are inexpensive and commonly used because they’re easy to install, maintain and repair. The downside is that they occasionally eject water. However, "spill-resistant" models are available for indoor installations. An air gap drain is required if the valve is installed in a basement or other interior space.


  • Installed 12 inches above the highest downstream point
  • Not allowed where back-pressure is a potential threat
  • Vertical, with the inlet at the bottom
  • Back-siphonage only
  • No chemigation

3. Double check valves (DCV)

DVCs are a good choice of backflow preventer for underground or indoor (in-line) installations. Unlike PVBs, DCVs do not have to be installed 12 inches above the highest point in the system. Some areas do require above-ground installation, so check with authorities before installing below ground.


  • Installed either above ground or inline (underground)
  • Installed horizontally or vertically, but horizontally is preferred
  • Protects against back-siphonage and backpressure
  • No chemigation

4. Reduced pressure zone assemblies (RPZ)

Although the most expensive, RPZs are the most versatile, secure and reliable of all backflow prevention devices. Choose an "inline" or "straight" configuration for installation underground. For above-ground installation, consider an "n" configuration assembly for a very small footprint.

  • Assembly:
  • Protects against back-siphonage and backpressure
  • Chemigation is approved
  • Horizontal installation required, unless factory-configured for alternate installation

Backflow testing in Calgary

If you suspect your property may need backflow testing, contact the friendly, knowledgeable plumbers at Commercial Mechanical.

We’ll inspect your backflow system and provide you with an assessment and estimate should you need to have new backflow devices installed on your property in Calgary. Contact us today!


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