Where does the backflow preventer go?

alan_s_thefirstJuly 28, 2012

I'm roughing in a future connection to my watering system (was decommissioned some time ago, so I'll have to do some repairs to get it working) in a spot that's going to be insulated in such a way it'll be hard to plumb.

So, question is, which order is it? Watering system shutoff with drain, then backflow preventer, or is it the other way? I'm assuming the latter.

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The backflow preventer goes between the shut-off valve and the watering system.

    Bookmark   July 30, 2012 at 2:52PM
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Ok, thanks. I was a bit puzzled by that, and couldn't see any literature anywhere. So I guess a drain on the shutoff is mandatory so you can drain the water between the shutoff and the backflow/check valve.

    Bookmark   July 30, 2012 at 3:09PM
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Now I'm puzzled. How do you drain the system at the end of the season if the backflow preventer is after the drain.

    Bookmark   July 30, 2012 at 8:51PM
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Hm. Around here, they get people to come round with a big compressor, open all the sprinkler valves, and then pressurise the system from a hosebib. I don't know if the compressed air would be good for the check valve. I would have thought the backflow preventer went before the shutoff, but that'd leave water sitting between the two for months. Maybe a shutoff before and after is better??

    Bookmark   July 30, 2012 at 11:50PM
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These things:

The body of the valve can be drained if needed.

It needs to go between the supply line and the ON/OFF valves ... in AZ, code requires either one in the supply line before the manifold, or one to each valve in the manifold.

The important part is they have to be the highest part in the system, so they can work properly.

    Bookmark   August 1, 2012 at 8:49AM
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I was actually going to use the item below which is what I've seen plumbers use for watering systems in the places I've worked on. They're required in new construction here but I don't think they were mandatory back in the day. Naturally, I think they're a good idea and I'd be doing anything to current code.

Here is a link that might be useful: Watts Dual Check

    Bookmark   August 3, 2012 at 12:23PM
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