Backflow preventer in Water Meter?

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by Wayne Lippman, May 23, 2020 at 2:00 PM.

  1. Wayne Lippman

    Wayne Lippman New Member

    Apr 13, 2020
    canandaigua, NY
    Lowe's website says that houses built since 1985 have backflow preventer built into the water meters. Googling seems to say that only houses with sprinker systems have them. Which is true?

    Before I put an expansion tank on today my pressure would go from 50 (where the PRV was set) up to 90 (which is the feed pressure); so I presume my 2006 house doesn't have one; but I could be wrong.
  2. fitter30

    fitter30 Active Member

    Feb 2, 2020
    Retired service tech
    Peace valley missouri
    You would have to check with your water purveyor. In Missouri as a state certified tester, houses only get a rpz backflow on sprinkler systems that have to tested once a year and certified. Cities and counties can spec other like a boiler. Commercial is total different.
    Last edited: May 24, 2020 at 9:57 AM
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  4. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Sep 2, 2004
    Retired Systems engineer for defense industry.
    New England
    The feds have been pushing utilities to add check valves for a long time now. While it doesn't happen often, and the specific circumstances don't occur that often, it is possible to pollute the supply system without one. It's a matter of time before all of the utilities install one, if they haven't already. Where I live, it's been code to have an expansion tank for decades to account for the fact that the utility is working its way through all of their customers, installing check valves.

    This is different that what is required for a sprinkler system, where a simple check valve doesn't normally suffice.
  5. WorthFlorida

    WorthFlorida The wife is still training me.

    Oct 28, 2009
    Orlando, Florida
    You are getting the two mixed up. Most water companies are adding backflow preventers just pass the meter. Without one as the water expands from heating, it can be pushed back into the main line. A backflow preventer can be different for a sprinkler system. It is a vacuum breaker type or double check valve installed just before the irrigation system. Though both may be called the same and have similar function, there are many different designs for it particular use. One designed for a sprinkler only cannot be used on your water supply line. A home with city water used for irrigation and domestic use could have two backflow preventers.

    Google "backflow preventer diagram" and you'll see different designs.
    Last edited: May 24, 2020 at 5:08 AM
  6. Bannerman

    Bannerman Well-Known Member

    Mar 19, 2014
    Ontario, Canada
    The 'PRV' you mention is a Pressure Reducing Valve or Pressure Regulator Valve, which itself will prevent backflow back into the municipal distribution system.

    Once a PRV is added, an expansion tank will be needed as cold water that expands when heated in the water heater, will have no place to expand to when no water is being drawn. This will result in excessive pressure on the home side of the PRV.

    When there is no backflow prevention device, cold water that expands in the WH will simply push back into the town's distribution system and the home pressure will remain at the usual pressure delivered from the town.
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