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I want to install an above ground irrigation system for our flowers (large flower farm). The part I am having trouble with is how to properly connect to the main water supply without having backflow. I would like to have a setup like below (I will add a blowout to prevent pipe freezing).
enter image description here

The pipe that goes underground will tee off, one end going to a garden faucet, and the other end to the irrigation lines. The pipe will travel 100-150 feet underground and eventually end up 5 feet higher than its starting point. This means it will be above the faucet at its end point. I am unsure what type of backflow prevention I would need, and where I should put it. I figure I need something in the mainline before the tee in the picture, but am not sure what. I read that RPZ is "the best" but am worried about potential flooding.

Also, I live in Maryland and am on Well Water.

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Generally you want the backflow as close to the supply as possible. So right here might be a good choice:

enter image description here

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  • Can you install a backflow preventer at a tee? Should it be slightly to the right of the tee? Or perhaps I am thinking of things incorrectly...
    – math314
    Apr 5 at 17:22
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    Backflow preventer is also called "vacuum breaker". It's a device that will allow air into the pipe if pressure falls. Generally you want it at a high point so that there is no standing water exerting pressure on it. It could be placed anywhere along your "House Service Line" to "Faucet" line.
    – jwh20
    Apr 5 at 17:34
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Since you're on well water I would think a regular check valve on the pipe right out of the house would be all you'd need. I know the RPZ's are good but awful expensive.

If your line is copper, SharkBite makes one that's easy to install similar to the one pictured below.

enter image description here

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  • Do you have a specific check valve in mind?
    – math314
    Apr 5 at 17:25
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To be code compliant in most areas you need a double check valve going to your irrigation system such as below. You don't needvacuum break control valves, in fact, they are problematic going uphill...just a regular electrically operated irrigation valve.

Sorry, JACK, but your solution doesn't meet code in most areas.

Double check valve

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  • Thanks for the great answer! Although your solution might be the best, do you have any comments on how it compares to the answer given by @jay613? Your solution appears to be more aesthetically pleasing, but if that didn't bother me, would a properly installed atmospheric pressure breaker work as well? Would you say an atmospheric pressure breaker is code compliant in most areas of the country?
    – math314
    Apr 6 at 11:10
  • You'd have to check with your AHJ for regs. there. In my area you now not only need to have a double check valve on irrigation systems, but if you are connected to a municipal or public water system, you need a double check valve at the meter that supplies the house/property/building. BTW, all the little connections on the pictured valve are for testing for proper operation. Apr 6 at 14:30
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Where I live what is most common is an atmospheric vacuum breaker. They are much cheaper than double/triple check backflow preventers. You would install it on the section of pipe that you labelled "house service line" with a reverse U that raises it above the highest point in your irrigation system.

I do not know if there are code reasons or other reasons why you might need one or another. My case is utility-provided water feeding a residential irrigation system on fairly flat ground and not connected to any chemical fertilization equipment.

I believe that if you have substantially high pressure, sewage or poisons downstream of the valve you need something different to what I have. A 5-foot rise might make this awkward, as the valve would have to be about 6 feet above the ground.

Not shown in this picture but you usually have shutoff and blowout valves adjacent to this breaker.

enter image description here

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