Is a check valve sufficient for backflow prevention?

Discussion in 'Irrigation / Sprinkler Forum' started by gonif, Jun 20, 2007.

  1. gonif

    gonif New Member

    Messages:
    8
    Location:
    Orange County, CA
    Hi everyone,

    I'm fairly new to irrigation, but I'm learning a lot as I go about installing a drip system into my back yard. My question is this: is a check valve good enough to satisfy backflow prevention for a drip system, or do I need something else?

    My water source will be tee'd off of the pipe that feeds a hose bib in the back yard, so the supply pipe will travel down a couple feet until it hits the ground, enters the valve box, and goes to the check valve, pressure regulator, screen filter, and manifold. The irrigation supply company I went to sold me a plastic check valve and said that would be sufficient, but I can't find anything online that even mentions this type of backflow preventor. They first brought out a heavy brass device, but then one of the guys there said that was overkill and a simple check valve would be fine for my small yard.

    What do you think, is this suitable or do I need something more beefy? Also, I understand that a true vacuum breaker needs to be installed above the highest sprinkler, but since my water supply is even higher than that then will that cause a problem?

    Thank you!
  2. Cass

    Cass Plumber

    Messages:
    5,980
    Location:
    Ohio
    Mos jurisdictions require a back flow preventer and not a check valve.
  3. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    Local codes spell out backflow prevention requirements. In general, a check valve is NOT adequate. Pressure vacuum breakers, or atmospheric vacuum breakers, or anti-siphon valves, must be installed above the heads.

    In your case, the RPZ device ( probably the large brass device they showed you) is the only option.
  4. gonif

    gonif New Member

    Messages:
    8
    Location:
    Orange County, CA
    Ok, thank you. I do want to do this the right way. Does it matter that the original water source is 2 feet higher than the RPZ device would be? In other words, the copper supply line will descend 3 feet from the hose bib tee to ground level, then go back up 1 foot to the RPZ device, then back down to the valve manifold, which is underground. Is this ok?
  5. Kiril

    Kiril New Member

    Messages:
    87
    Location:
    Sacramento, CA
    If your running the irrigation line directly off the hose bibb, then most likely all you will need is a MHT x FHT hose BPD (backflow prevention device).

    http://www.watts.com/pro/_products_sub.asp?catId=65&parCat=102

    Otherwise you will need something more, such as an above ground valve with a built-in BPD:

    http://www.irritrol.com/valves/valves_2700s.html

    Or one of the non hose type BPD's at the bottom of the Watts page from the first link above.

    In both cases, it's best to check with the local BD to see what their requirements are.

    In my area (NorCal), code requires a BPD be installed 12" above the majority of the downstream outlets regardless of what height the water is originally coming from. If your going to do as you suggest above in your last post, I would run the initial line from the source pipe down to the same level as the valves, back up to the BPD, then back down to the valves.

    I have also plumbed the BPD directly into the source line from the house, but you need to be careful to provide support for it or the fitting (usually inside the wall) may develop a leak over time. Make sure you include unions on both legs of your BPD and a shutoff valve.
    Last edited: Jun 21, 2007
  6. Gary Swart

    Gary Swart In the Trades

    Messages:
    7,349
    Location:
    Yakima WA
    Double check BGPs can be mounted under the ground surface and do not have any restrictions about the elevation of the sprinklers. These would be just below the surface of the ground, in a control box, so they are considerably higher than the supply line coming from the meter. You do have to use great care in winterizing them. I remove mine completely each fall for that reason. There are other methods of backflow pevention, but the double check seem to be more sensible than others, at least to me.
  7. Last sprinkler system I had to connect to off the potable water system was a RPBA which was a little overkill given the system had no chemical injection setup.

    A DCVA would of been the equivalent to the need.
  8. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,636
    Location:
    Cave Creek, Arizona
    backflow

    An atmostpheric vacuum breaker cannot be used if there are control valves downstream from it. The least level of protection in most areas is a pressure vacuum breaker. Some areas require a reduced pressure device, but in most cases it is not necessary.
  9. gonif

    gonif New Member

    Messages:
    8
    Location:
    Orange County, CA
    Wow! Thanks for all the great information, you guys. This is very helpful and I hope it can help future readers as well. If you can believe it, I also had contacted my city's Building & Safety department and the guy thanked me for wanting to do the right thing but then really didn't have any information. He recommended that I went with any UL-approved device. :confused:

    So if I could ask one more follow-up question, please. The irrigation store I went to sold me an anti-siphon valve to use as a Master Valve. It's a Hunter ASV-075 (http://www.hunterindustries.com/Products/Valves/asvspecs.html). Is this acceptable to add backflow prevention to the system? What's confusing me is that all descriptions of atmospheric vacuum breakers say that control valves can't be located downstream of them -- but maybe that only applies to atmospheric breakers that don't have their own valve attached to them.

    What do you think, will this type of valve work as a backflow preventer?
  10. Mr_Pike

    Mr_Pike New Member

    Messages:
    136
    Location:
    Nebraska
    Do not use a double check if you are using any sort of natural water source such as a lake or stream. The fine sand that is inherent in these systems will likely cause a failure in these types of spring tensioned devices.

    They do have there places, but are not legal in a lot of states. Where they are legal, it is the best option for when a BFPD is needed on the interior of the structure as they are sealed and will not "burp" when a valve closes or during startup.
  11. Wet_Boots

    Wet_Boots Sprinkler Guy

    Messages:
    798
    Location:
    Metro NYC
    The OP is in California, which I believe got rid of the Double Check Valve Assembly quite a while ago. (It isn't rated to protect against toxic backflow) If the water source is higher than any part of the drip system, then a vacuum breaker would suffice for the required toxic-rated backflow protection, provided that there are no valves downstream of the vacuum breaker. The antisyphon valve mentioned, would also provide toxic-rated protection, with the same requirement of there being no valves downstream of it.
  12. gonif

    gonif New Member

    Messages:
    8
    Location:
    Orange County, CA
    So if I can't use that antisiphon valve as the Master valve, the it sounds like I need to rebuild my manifold. The whole reason they sold me the antisiphon valve/Master valve in the first place is because I had already built my manifold with control valves that don't have any backflow prevention built in. It seemed like the work around was to add a Master valve that did have backflow prevention, nice and tidy.

    So is there a different type of Master valve that I can add with backflow prevention, or am I just plain out of luck here? Do I need to rip out the manifold and replace each valve with an antisiphon or something similar?

    Sorry for all the questions, this is really complicated to me, and my city clerk and the irrigation store seem to be giving questionable answers.

    Thanks!
  13. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,636
    Location:
    Cave Creek, Arizona
    valve

    You do not have to redo the manifold. Just purchase a pressure vacuum breaker and properly install it between the water line connection and the manifold. That main line valve would fit into a "gray" area, because when the valve is closed there is no pressure on the vacuum breaker so the downstream valves would not be a factor.
  14. Wet_Boots

    Wet_Boots Sprinkler Guy

    Messages:
    798
    Location:
    Metro NYC
    Now that you made it clear that there is a manifold of valves to protect, then you can just move up to a backflow preventer that's designed for continuous pressure. If your location is at least a foot higher than any of the sprinkler heads or pipes, then the PVB will work just fine. If the elevations are against you, that's when you have to use the RPZ device.
  15. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    The RPZ must be above ground. It cannot be in an undergrade box
  16. gonif

    gonif New Member

    Messages:
    8
    Location:
    Orange County, CA
    That's great, thank you to everyone for taking the time to reply! I returned that master anti-siphon valve and bought a pressure vacuum breaker, which I'll install 12-18" above the highest water outlet downstream.

    Thanks again, I'd have been stuck without you guys.
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