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Old 11-21-2012, 06:04 PM
Darryl G Darryl G is offline
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Backflow Preventer Questions

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.

Darryl
  #2  
Old 11-21-2012, 06:42 PM
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irritation irritation is offline
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You should know. You've been around a long time. Common sense says yes.
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Old 11-21-2012, 07:08 PM
Darryl G Darryl G is offline
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I've been around for a long time but I'm not an irrigation guy

How can I determine if this is the problem?
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Old 11-21-2012, 07:28 PM
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irritation irritation is offline
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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  
Old 11-21-2012, 07:30 PM
bcg bcg is online now
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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  
Old 11-21-2012, 07:37 PM
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cjohn2000 cjohn2000 is offline
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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.
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Old 11-21-2012, 07:42 PM
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irritation irritation is offline
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Quote:
Originally Posted by cjohn2000 View Post
In areas where it doesn't freeze they use PVBs, pressure vacuum breakers.
Wrong, PVB's are the the most common here. RP's if elevation is a factor.
  #8  
Old 11-21-2012, 07:48 PM
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cjohn2000 cjohn2000 is offline
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Quote:
Originally Posted by irritation View Post
Wrong, PVB's are the the most common here. RP's if elevation is a factor.
I guess I was thinking more about California.
  #9  
Old 11-21-2012, 07:51 PM
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Wet_Boots Wet_Boots is offline
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where the $#%^&*@# is the OP's location - we got location-specific knowledge and advice, along with zero interest in playing guessing games
  #10  
Old 11-21-2012, 07:53 PM
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Mike Leary Mike Leary is offline
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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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