basic antisiphon set up w/4-5 zones

Discussion in 'Irrigation / Sprinkler Forum' started by bloocruiser, Feb 25, 2008.

  1. bloocruiser

    bloocruiser New Member

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    1
    Hello all,This is my first post here... so glad I found this forum. I'm getting ready to dig up my yard to put in a sprinkler system. I'm looking at 4-5 irrigation zones. My question is if I use 4-5 automatic in-line valves can I get away with using one antisiphon valve before the manifold? Does anyone have a diagram or schematic drawing of a basic 4-5 zoned set up? Thanks in advance,george
  2. Wet_Boots

    Wet_Boots Sprinkler Guy

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    798
    Location:
    Metro NYC
    The answer to your question is no. Each of the valves would have to be antisyphon. Hopefully you are on flat ground, because the valves have to stand higher than the sprinkler heads and pipes.
  3. Gary Swart

    Gary Swart In the Trades

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    7,328
    Location:
    Yakima WA
    Since you are concerned with antisyphon valves you must be using domestic water. Here's a brief description of my system that has worked well for over 20 years. I have a tee in the main supply line. One side of course if for the house and the other is for irrigation. I have a stop and waste valve in the irrigation line right after the tee. From the tee, I come up with 1" copper to about 18" below the surface of the ground. That's where my back flow preventer is located. This is a Watts unit that is attached to the intake and outlet pipes with unions. The outlet pipe is 1" copper for about 3" then transitions to 1-1/2" PVC that runs 30' to my manifold which has 4 electric valves. The zones branch for there. I also have one 1" PVC that is under pressure at all times for hose bibs. Everything is underground. In the fall, I remove the back flow preventer and blow each zone with compressed air. The back flow preventer is stored inside just to be absolutely certain it will not freeze if I don't get all of the water out. In the spring or early summer, my city requires the back flow be recertified by a licensed inspector. With my system, the controller is located in my basement just inside of where the manifold and valves are located so there is no lengthy wiring to worry about.
  4. Wet_Boots

    Wet_Boots Sprinkler Guy

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    798
    Location:
    Metro NYC
    Washington State doesn't yet have the requirement that the lawn sprinkler backflow be toxic-rated. While cheaper than the DCVA used in WA, the antisyphon valves are toxic-rated and can comply with the higher standards of other states.
  5. Gary Swart

    Gary Swart In the Trades

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    7,328
    Location:
    Yakima WA
    Guess I'm behind times. I have no clue what this "toxic rating" is.:confused: I would have to assume Wet Boots is correct however, what I use now is the same as I started with 20+ years ago. I did have tor replace the original BF preventer a number of years ago, but the replacement was essentially the same as the original. I'll take this as a heads up for something that will probably become a requirement for me sooner or later. Thanks!:)
  6. hj

    hj Moderator & Master Plumber Staff Member

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    26,481
    Location:
    Cave Creek, Arizona
    Bfp

    A single approved antisiphon/backflow preventer DOES replace the individual ones on the valves. However, the ones on the valves are atmospheric type, while the common one has to be either a pressure or reduced pressure principal one, depending on your area's requirements.
  7. Wet_Boots

    Wet_Boots Sprinkler Guy

    Messages:
    798
    Location:
    Metro NYC
    Remove the word 'antisiphon' to be more correct, since that word is allied with the combination of shutoff valve and atmospheric vacuum breaker, known as an antisiphon valve. When you use antisiphon valves as the means of backflow prevention, you must use one antisiphon valve for each zone, because there can be no valve downstream of an atmospheric vacuum breaker. This is an important point, because an atmospheric vacuum breaker will not function if it is pressurized 24/7 (and you don't get to claim the the downstream zone valves are always in perfect working order - backflow preventers are 'self-contained' and not dependent on other devices)

    The "toxic" question comes in when codes take into account the nature of the possible backflow. If the code declares the water in a sprinkler system to be toxic, then the backflow preventers required by the code will be rated to protect against toxic backflow. Double Check Valve Assembly devices are not rated for toxic backflow, so they are no longer approved by many states.

    There are two ways to define the dividing line on backflow, and lawn sprinkler systems can be on one side or another. If the words "toxic" and "non-toxic" are used, the sprinkler system will very likely be defined as toxic, and the code will not allow the DCVA. If, instead, the words are "high-hazard" and "low-hazard", then the lawn sprinkler system may be classified as low-hazard, and the DCVA can be used.

    If someone asks about lawn sprinkler backflow, I would point them towards backflow that is toxic-rated, because codes get tighter, but rarely get looser, and old backflow is not likely to be grandfathered when codes get tighter. And since most posts do not state a location, I would never assume the poster could actually use the DCVA.

    The least expensive single device for backflow prevention, upstream of a group of zone valves, is the Pressure Vacuum Breaker. It is toxic-rated, and must be installed so that the device is at least a foot higher than any pipe or sprinkler downstream of it.
  8. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,481
    Location:
    Cave Creek, Arizona
    definition

    Remove the word 'antisiphon' to be more correct,

    Remove that recommendation to be correct. The pressure vacuum breaker/backflow preventer does both. The air gap/float performs the "antisiphon" feature, and the spring loaded piston does the backflow function. A simple check valve will prevent/minimize backflow, and an atmospheric vacuum breaker will take care of siphonage. But NEITHER can perform both functions.

    I do not know of any code that ever approved a DCVA for irrigation purposes, since siphonage was always the major concern, given that there was seldom any way for the downstream portion to be independently pressurized, unless it was a dual fed system and that creates its own set of problems.
    Last edited: Feb 29, 2008
  9. Wet_Boots

    Wet_Boots Sprinkler Guy

    Messages:
    798
    Location:
    Metro NYC
    My point is to avoid confusing the folks asking questions, and to emphasize the wisdom of never using the word "antisiphon" in connection to a Pressure Vacuum Breaker. Other terms can describe its functions.

    You haven't been getting around. The DCVA is standard irrigation usage in the state of Washington, and in others as well. Many towns in New Jersey had ordinances requiring DCVA usage. That made things interesting when the state moved to use BOCA codes and the National Standard Plumbing Code, which removed the DCVA from irrigation usage.
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