Backflow Preventer Questions

Discussion in 'Irrigation' started by Darryl G, Nov 21, 2012.

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  1. Darryl G

    Darryl G Inactive
    Messages: 9,500

    Hi guys. I'm wondering if you guys could answer some questions about backflow preventers for me. I'm not an irrigation guy, and this is actually related to volunteer efforts on my part to try to solve a mystery for a local municipality. They are getting fecal coliform contamination in a well at their athletic complex as an ongoing problem. The well provides water for their snack bar and water fountains as well as their irrigation system. It's a drilled bedrock well, so I think it unlikely that the groundwater in the area is contaminated, although it is posslbe.

    Possible sources of the contamination that I have identified are:

    1) Surface water leaking into the well head (someone is inspecting the well for me today to let me know if it's flush with grade or elevated)
    2) A bad well seal around the well casing allowing water to flow around the outside of the casing, and
    3) Possible backflow from their irrigation system

    This field does get a lot of geese on it, and I'm thinking that perhaps they're getting backflow from the irrigation system into the well. So what exactly is a backflow preventer? Is it like a check valve? Do they fail sometimes (I would imagine so)? How does one typically test one? Is there usually just one on a system or multiple?

    I have no idea what their irrigation setup is and it's not likely I'll have that information readily available. I guess I just want to know a little more about backflow preventers and if it's possible that a failed one (or lack of one for that matter) could be causing surface water to flow back into the well.

    Thanks in advance.

  2. irritation

    irritation LawnSite Gold Member
    Messages: 3,594

    You should know. You've been around a long time. Common sense says yes.
  3. Darryl G

    Darryl G Inactive
    Messages: 9,500

    I've been around for a long time but I'm not an irrigation guy :)

    How can I determine if this is the problem?
  4. irritation

    irritation LawnSite Gold Member
    Messages: 3,594

    Examine the irrigation supply and the feeds for the snack bar and water fountains. If they supply all and there is no backflow preventer in between, there could be a serious problem.
  5. bcg

    bcg LawnSite Bronze Member
    from Tx
    Messages: 1,865

    Locate the cross connections, make sure valves are installed (if not, hire someone to install them) and then hire a BPAT to test them.
  6. cjohn2000

    cjohn2000 LawnSite Senior Member
    Messages: 570

    I don't know what area your from, but over here the most common bp is the doublecheck, 2 spring loaded check valves, one after the other, usually mounted in a box below grade.

    In areas where it doesn't freeze they use PVBs, pressure vacuum breakers.
    PVB has single check valve protecting the incoming water. Any water trying to "Flow back" goes out the top of the unit, since the top is vented. Another form is the little screw on deals that can be added to outdoor faucets.

    Atmospheric vacuum breaker is like the PVB except the check isn't spring loaded and the unit is not testable. Usually they are molded with the solenoid control valve. In our area ( as far as I know) Atmospheric vacuum breakers can be used but one for every solenoid control valve and they need to be mounted 6-12" above the highest head.

    Last is the Reduced pressure backflow preventer like a double check except their is a vent that opens between the two checks should the second check fail.

    All my own understanding of the different devices.:waving:
  7. irritation

    irritation LawnSite Gold Member
    Messages: 3,594

    Wrong, PVB's are the the most common here. RP's if elevation is a factor.
  8. cjohn2000

    cjohn2000 LawnSite Senior Member
    Messages: 570

    I guess I was thinking more about California.
  9. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Messages: 50,757

    where the $#%^&*@# is the OP's location - we got location-specific knowledge and advice, along with zero interest in playing guessing games :realmad:
  10. Mike Leary

    Mike Leary LawnSite Fanatic
    Messages: 23,171

    My guy failed his backflow re-cert because of the part concerning PVBs; they are not permitted in our market area, and, hence we had none in service and had no working experience with them. Go figure backflow regs all around the country, seems to me it should all be the same. :dizzy
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