The right backflow preventer is determined by hazard level and local code, not preference. High-hazard connections require a reduced pressure zone (RPZ) assembly; lower-hazard ones may allow a double check valve; irrigation commonly uses a pressure vacuum breaker.

The Main Types

  • Reduced pressure zone (RPZ) assembly. The highest level of protection, with two check valves and a relief valve between them that discharges if either check fails. Required for high-hazard applications — anything where backflow could introduce something genuinely harmful. It must be installed above grade and needs drainage for the relief discharge.
  • Double check valve assembly (DCVA). Two independent check valves in series. Suitable for lower-hazard connections where backflow would be a nuisance rather than a health risk. Can be installed in a below-grade vault in some cases.
  • Pressure vacuum breaker (PVB). Common on irrigation systems. Protects against back-siphonage but not back-pressure, and must be installed above the highest downstream outlet.
  • Atmospheric vacuum breaker (AVB). The simplest, used on individual hose bibs and specific fixtures. Limited application.

What Determines Your Requirement

The hazard level of what is downstream — irrigation with fertilizer injection is treated very differently than a simple sprinkler system. Whether back-pressure is possible in addition to back-siphonage. Installation location and freeze exposure. And local water authority requirements, which are the final word and vary by jurisdiction.

Freeze Exposure Matters Here

Worth planning for. Many assemblies sit outdoors on irrigation systems, and a New Mexico hard freeze will crack an unprotected one. Whichever type you install, it needs winterizing — drain and insulate, or shut down and drain the irrigation system before the first freeze.

The Related Detail

A backflow preventer creates a closed system, so thermal expansion from your water heater has nowhere to go. Without an expansion tank that shows up as a weeping T&P valve — frequently misdiagnosed as a bad valve.

Testing

Annual testing by a certified tester is required for most assemblies. Contact B. Carlson about backflow prevention in Albuquerque.