Can you install dual check valves underground for irrigation system?

Discussion in 'General Plumbing Help' started by Fusion916, Oct 10, 2013.

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  1. Oct 10, 2013 #1

    Fusion916

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    I'm going to redo my irrigation system and instead of using the above ground anti-spihon valves I want to install a dual check valves and then inline timer valves.

    The DC valve im thinking of getting is this one:

    http://www.amazon.com/Wilkins-Reduc...&keywords=Wilkins+3/4+inch+double+check+valve

    I want to install both the DC valve and inline valves underground. Is that allowed in CA? I know anti-siphon valves have to be (I think) 12 inches above the highest sprinkler, but don't know if that also applies to the pro grade DC valves.
     
  2. Oct 10, 2013 #2

    johnjh2o

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    First off that's not a dual check. It's an RPZ device. (reduced pressure zone) That device can not be installed under ground. A dual check is not and approved device because it can't be tested. You may be thinking of a DBL check. That device has test cocks a dual check doesn't. Both the RPZ and the DBL check are much more expensive then the PVB
    (pressure vacuum breaker). What is your reason to not use the approved device for your irrigation system. (PVB)
     
  3. Oct 10, 2013 #3

    Chris

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    We install that very device here in Southern CA in many commercial irrigation lines but I have never installed one under ground, they have always been brought above ground with an air gap under then back down under ground. I am also curious of why you are not going with the norm?
     
  4. Oct 10, 2013 #4

    Fusion916

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    Is a RPZ and double check the same except the pressure reduction? It looks the same:

    http://www.amazon.com/Wilkins-Doubl...26&sr=1-1&keywords=Wilkins+double+check+valve

    I'm 100% sure the double check and RPZ devices are approved where I live because I literally see them everywhere on commercial properties. I have never seen that PVB devices anywhere in CA so I don't think that's legal here.

    The reason I'm looking to get a separate check valve is so I don't have to use those above ground anti-siphon valves, but instead use a bunch of buried inline valves. Even if I have to elevate the double check, it would only be one thing elevated while I can bury the many inline valves I need.
     
  5. Oct 10, 2013 #5

    johnjh2o

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  6. Oct 10, 2013 #6

    Fusion916

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    Given it is, does this also need to be elevated above ground? and if so, by how much?
     
  7. Oct 12, 2013 #7

    chukar

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    I believe it has to be at least 12" about your highest outlets or feed. So if your property is flat it's like 18" off the ground to the center line radius, but if you have a sprinkler head that is going to be taller then that on say a sloping years you have to raise it up. A PVB protects against back siphonage only, not back pressure. A double check valve will protect against back pressure and can be installed in a pit, assuming you have proper clearances.
     
  8. Oct 13, 2013 #8

    Fusion916

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    What is the difference between back siphonage and back pressure?
     
  9. Oct 13, 2013 #9

    Caduceus

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    Back pressure is when additional pressure is created within the water system after the service, such as thermal expansion, and puts pressure on the incoming service. Back siphonage is when a negative pressure is created before the service causing the water to be drawn back towards the water service.
    Positive for one, negative pressure for the other.
     
  10. Oct 14, 2013 #10

    Fusion916

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    Why (for residential use) do you need to protect from anti-siphon but not back pressure? Do check valves protect from both? Most residential sprinkler valves are anti-siphon valves but say nothing about protecting from back pressure. Do the industrial check valves (the big double check valves) protect from both?
     
  11. Oct 14, 2013 #11

    chukar

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    You don't need to protect from back pressure unless you have something to create it like a pump or an elevation gain in your piping, this why when you install a PVB you do it above the highest point in your irrigation piping. Doing so also lessons the cost of the install, and servicing later.

    When we install a back flow preventer we do so based on a threat to health check list, depending on your application we will increase the types of protection.
     
    Last edited: Oct 14, 2013
  12. Oct 14, 2013 #12

    Fusion916

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    So pumps anywhere on the residence after the service main will cause backflow, understood. Make sense why backflow preventers are needed for commercial properties with fire hydrants than.

    So if the only thing harmful on the service main is an irrigation system, then only an anti-siphonage device is needed?
     
  13. Oct 15, 2013 #13

    chukar

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    If only it were so simple, keep in mind a pump could create siphonage behind it. Also some area's use grey water (recycled water) for irrigation that will increase the amount of protection required. Also do you intend to put in fertilizer to be distributed through your system, or other chemicals.

    For my house I installed an RPBA I wanted the best protection for my family while also giving me the option to expand the system down the road with above ground water for hanging plants and such.

    We have plans to put in a back deck, I wanted to be able to have hanging plants with there own watering system. Beyond that you need to ask what your local water authority requires.
     
  14. Oct 15, 2013 #14

    Caduceus

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    Okay, maybe my input will help you to finalize your decision as to what is an appropriate backflow device for your irrigation system.
    Back siphoning and back pressure are both important concerns with irrigation systems, no just back siphoning.
    Most irrigation systems are less than a foot below the soil surface. Whether it is copper or plastic piping, the piping arrangement is considered a 'closed system' when a solenoid valve and any backflow device is added to any part of the arrangement...even if the only device is on the house service.
    The shallow piping subjects the pipes to expansion and contraction from heat and cold from the surface and can produce a pressure situation, not just a siphon situation. With the risk of chemical infiltration from your yard, neighbor's yards and other public sources, a testable RPZ is the only approved device for my area. A testable double check is good, but still not approved. ASSE requirements may specifically state the need for an RPZ when glycol antifreeze is used for winterizing, but locally the risks are observed as the same when it come to pesticides, herbicides or other surface chemicals.
    For these reasons, if I had an irrigation system, I would protect my family with ONLY an RPZ device. Nothing else would even be a consideration.
     
  15. Oct 15, 2013 #15

    Fusion916

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    So after all of the discussion, for an irrigation system, the anti-siphon/backflow preventor that is recommended is an RPZ device, such as the one in the OP (Wilkins 3/4" 975XL)?

    EDIT:

    Actually, why do all sellers of this device say they can't ship to CA? Is this device actually NOT approved here?
     
    Last edited: Oct 15, 2013
  16. Oct 15, 2013 #16

    Chris

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    I believe they have to be lead free in ca now. We install that device often.
     
  17. Oct 15, 2013 #17

    Caduceus

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    Yes, after all of the discussion...but keep in mind that the discussion was started to clear up the differences between what was written in text and shown in a photo. In the plumbing world, calling an RPZ a double-check is a red flag that the products are not understood for what they are and for their uses.
    As the discussion continued it was important to explain the importance of these differences, since you are the person who will ultimately be responsible for the end result.
    Sharing information and having an open discussion in order to learn more about something is a good thing.
     
    Last edited: Oct 15, 2013
  18. Oct 15, 2013 #18

    Fusion916

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    Do you have a link that has the lead free version?
     
  19. Oct 15, 2013 #19

    Fusion916

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    Understood, I have to admit I know next to little about plumbing but am learning. Just to be clear though, a RPZ device will prevent both backflow and siphonage right? Meaning between the water main and the irrigation, this is the only device I need?
     
  20. Oct 16, 2013 #20

    Chris

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