Backflow preventer. Basic questions

Discussion in 'Irrigation / Sprinkler Forum' started by ToolsRMe, Jun 2, 2007.

  1. ToolsRMe

    ToolsRMe New Member

    Messages:
    145
    Location:
    CO
    (1)
    My biggest problem is that my Wilkins 720A (http://www.zurn.com/operations/wilkins/pdfs/installation/IS720A.pdf) was not installed correctly by me ... at least according to Wilkins.

    Basically to make the plumbing simple, the backflow preventer is about 20 degrees off of horizontal. The tech support people at Wilkins tell me that any inspector (there won't be any) would not approve. Frankly, I don't care about inspection. I do care about contaminants flowing back into my home's potable water system.

    So, will being 20 degrees off of horizontal really cause a problem? I'm going to fix it, anyway, but I'm just curious.


    (2)
    The installation sheet says that the 720A needs to be 12 inches above the highest outlet. Does that include the "spray heads on risers" that could be a few feet off of the ground?


    (3)
    What's the basic idea about testing the backflow preventer? How often should it be tested? Can I do it?
  2. Gary Swart

    Gary Swart In the Trades

    Messages:
    7,359
    Location:
    Yakima WA
    #1 The reason for inspection is to verify the installation was done correctly, not to burden you with unnecessary work. Improper installation may be the reason your unit isn't working. In my city, if you don't have functioning backflow device, your water will be shut off.

    #2 I believe that's what it means. I use a different style preventer that does not have to even be above ground.

    #3 The purpose of these devices is to prevent contaminated water from your irrigation lines from getting into your or the city's water supply. The testing process requires special instruments and some training so it is not really a DIY job. This is especially true if your device has to be officially certified each year. Testing should be done each spring to make sure the unit is still work properly.
  3. ToolsRMe

    ToolsRMe New Member

    Messages:
    145
    Location:
    CO
    I actually went to my city and they do not require a permit. Weird given how much this city is "control freakish." But the guys at the help desk were very helpful

    I believe that you are talking about a "double check" system that uses springs instead of vacuum to prevent backflow. Which one do you use? Do you like it? Do you have it checked every year?

    So who does this? Landscaper? Plumber? How much should it cost?

    And my device doesn't even have to be certified ... but I'm anal so I'll have it done.

    What's strange is that most of the homes in my subdivision were built about 35 years ago and very few of them have backflow preventers on their irrigation system. Indeed, I'm installing a pair of backflow preventers (one on each leg of a tee) on an existing irrigation system.

    Is there anything wrong with having two backflow preventers in a row? What I mean is if I put a double-check backflow preventer before the water tees, will that cause problems?
  4. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,831
    Location:
    Cave Creek, Arizona
    backflow

    Only a registered tester can make the tests, partly because it takes a special instrument, and they are the only ones that usually have them.

    Two backflows in sequence only reduces your dynamic pressure and flow volume.

    The proper backflow device for sprinklers is usually a "pressure vacuum breaker" or a "reduced pressure principal" backflow preventer. The latter costing much more than the former, and being required in some areas.

    The backflow preventer should be 1' above the highest outlet, i.e., sprinkler head, or there is a possibility that its elevation induced pressure could simulate a backflow condition and cause the BFP to dump water periodically.
  5. Gary Swart

    Gary Swart In the Trades

    Messages:
    7,359
    Location:
    Yakima WA
    Yes, mine is a double check type. I chose this type because it could be located under the surface of the ground and did not have to be above the highest sprinkler. It was made by Watts. I looked on the Watts website but couldn't find one exactly like mine. It is somewhat similar in appearance to their 007 model, but since mine is several years old, it has probably been replace by a newer version. Since I am just a homeowner, I am not familiar with other types, this is all I have used since I installed the system in 1984. I can't recall how much it cost, but after almost 25 years, it wouldn't be a relevant figure anyway. I did have to have it repaired once, don't even remember what it needed for sure, but it was easily repaired. I also can't give you learned answers about the pros and cons of different systems. As HJ points out, the testing must be done by a trained, certified, and licensed technician. My city provides a list each year of companies and individuals that meet their requirements. I can choose anyone from the list. They come, test, and take care of the paperwork. The city inspects new installations, then it is done by these private contractors. The cost in past years has been $25, but this year I called a large landscaping company and it was almost $50. I don't know if I got ripped off or if everyone raised their fees. It does require special instruments that are not going to be found in every plumbers tool box. I assume in different areas, the rates may differ, so what it would cost you, I can't even guess. As I stated in my earlier posting, if I forget or try to slip by without the new certification, the city will give me a reminder, then shut my water off if I don't comply. (I forgot to get it done one year and received the reminder with warning of consequences) As you have already noted, your city apparently doesn't see the need for the use of backflow preventer, but they are widely used and required by cities around the country. I don't know what the odds are that if a dog took a dump on top of a sprinkler in an unprotected system that your water supply would be contaminated, but I sure don't think I'd want to gamble with my family;s health to save the cost of a backflow preventer or to save the cost of an annual inspection.
    It seems to me that you only should need one device. It probably should be near where the irrigation leg splits from the domestic leg.
  6. ToolsRMe

    ToolsRMe New Member

    Messages:
    145
    Location:
    CO
    Well, that answers that! Thanks!

    So if I'm not concerned about water being dumped out then I really don't have to care?
  7. Wet_Boots

    Wet_Boots Sprinkler Guy

    Messages:
    798
    Location:
    Metro NYC
    Just install the device according to the manufacturer's instructions. Buy some elbows. Stop trying to justify doing less. The Wilkins 720 is a good PVB, and if it's a foot-and-a-half higher than any pipe or sprinkler that's downstream of it, then it can pass inspections, and provide you the protection for which it was designed.
  8. Mr_Pike

    Mr_Pike New Member

    Messages:
    136
    Location:
    Nebraska
    I will have to get out my code book, but according to my supplier, a double check is not a legal backflow prevention device for new installation in our state. As a rule, we use Pressure Vacuum Breakers 99% of the time, and they should be located 12" above the highest head so the back pressure from the laterals would not activate the dump valve. This is sort of a fail safe thing, if by some freak occurance, your neighbor's house caught on fire, the day after you sprayed pesticide and fertilizer on your yard, and the run off from the fire department hosing your place down flooded your yard at the same time their pumper truck is sucking all the water out of the main, and your toilets and sprinkler lines. It is suppose to eliminate the risk of your heads collecting runoff and syphoning it back into your system. Will that appy to the shrub risers on the spray heads? Depends on the inspector I suppose. No one says they have to be installed at the time of inspection.
    Last edited: Jun 28, 2007
  9. ToolsRMe

    ToolsRMe New Member

    Messages:
    145
    Location:
    CO
    I installed both PVBs correctly ... so this is for my curiosity more than anything else:

    If the PVB is installed "too low", can polluted water flow backwards into my house or will it just dump water?

    If there are shrub risers (there are) that are above the PVB, can't the water in the riser push water from the sprinkler head back into the PVB? I'm thinking of a sprinkler head that is screwed into a tee and the shrub riser is further downstream. (Or does that violate safe practice?)
  10. Mr_Pike

    Mr_Pike New Member

    Messages:
    136
    Location:
    Nebraska

    I don't think it should dump or violate safe practice. The opening is so far above ground it is not likely to operate as a suction device for runoff. the back pressure caused by a few feet of riser is not likely to activate the PVB's backpressure dump valve. Most of the time it requires a fairly large amount of lateral line being above the PVB and an interruption in system pressure. This can occur if you have a large large slope (like 30ft or more).

    The main purpose for this rule, is to hopefully activate the dump valve with any sort of back flow occurance during an interruption to your supply pressure. Like due to a fire truck pumper, or a water main break down hill from your location. There are a lot of "what ifs and this also has to happen" in any sort of BFP talk. You are fine in my book, and are probably better off than 1/4 of the systems in my community that have NO BFPD because they were not code at the time of installation.

    I would probably fix your angled installation, more for winterization safety than anything else. The tilt shouldn't effect anything as far as operation to my knowledge, but I am not a BFPD engineer, just a ditch digger.
    Last edited: Jun 28, 2007
  11. ToolsRMe

    ToolsRMe New Member

    Messages:
    145
    Location:
    CO
    I did that already. What a pain.

    I had called the manufacturer and one of the engineers said "It has to be level". I then asked "What does that mean? How much angle is allowed?"

    The guy said "None." Which, of course, is a silly answer ... but I couldn't get anything like +/- 5 degrees, or whatever, out of the guy.

    So I installed it as level as I could.
  12. Wet_Boots

    Wet_Boots Sprinkler Guy

    Messages:
    798
    Location:
    Metro NYC
    What's such a pain about installing a backflow preventer on the proper plane? What kept you from doing it right the first time? "Twenty degrees off horizontal" is something you should take a photograph of.
  13. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,831
    Location:
    Cave Creek, Arizona
    valves

    Double checks are usually not acceptable because any check valve can fail without giving any outward signs of a problem. Buring them underground can immerse them in polluted water which could then be aspirated into the system. The 12" above the highest riser is irrelevent when there is a valve between the PVB and that highest riser, because the valve will prevent backflow unless the valve is open and the water supply is turned off, in which case the backflow would be a temporary aberation.
  14. GrumpyPlumber

    GrumpyPlumber Licensed Grump

    Messages:
    1,404
    Location:
    Licensed Grump
    2) YUP, often they wind up being installed inside a joist bay above the sill inside the basement ceiling if necessary (when inspected..which is a good idea)
    3) I think, if I recall..once a year (I could be wrong) you need certification to test them, most plumbers don't do it. (specialized training)
  15. ToolsRMe

    ToolsRMe New Member

    Messages:
    145
    Location:
    CO
    What was such a pain was that it had already been installed. That was my fault for not thinking it through.

    The copper that goes to the manifold was some kind of "flexible" 3/4" copper that they ran through the foundation wall. It then made a right-handed turn to run alongside the exterior foundation wall towards the manifold with a slope of about 20 degrees.

    What I had stupidly done was cut the line (on the 20 degree slope) and installed 90-degree elbows and then straight pipe to the backflow preventer.

    What made it such a pain was that

    a) I had to redo it.

    b) The trenching was done behind prickly shrubbery.

    c) There were 24V control lines going to valves near there and the line was fairly tight and it ran parallel to the copper at ground level. Digging is such sweet sorrow. OK, not sweet.

    d) I had to use 4 90-degree elbows in order to straighten out the connection and for a DIYer that turned out to be somewhat fun.

    e) Cleaning the copper that had been sitting in soil for thirty (?) years is something I don't really want to do again having now done it twice.

    Anyone want to see a picture of the connections? Just walk me through how to post a picture to this forum and I'll do it.
  16. Gary Swart

    Gary Swart In the Trades

    Messages:
    7,359
    Location:
    Yakima WA
    Well, we all live and learn! I have explored the subject a tad more, and find that indeed my BFP is a RPZ type, not a double check as I stated in an earlier post. It is very similar to those pictured on the Watts web site, the petcocks have a slightly different appearance, but essentially the same thing. Point is, this type does not have to be above the highest sprinkler. It can be below the ground level (not buried) in a control box.

  17. (KY) Testing is:

    1. When first installed
    2. Yearly
    3. Whenever moved or relocated

    You can not test your own backflow device. Takes either mechanical or computerized gauges that are never rented. The one who tests them must have a backflow license in the state they reside in along with a journeyman plumber's license.

    They are the only ones that have the ability to give a report on that device.
  18. Wet_Boots

    Wet_Boots Sprinkler Guy

    Messages:
    798
    Location:
    Metro NYC
    One does have to cut the manufacturers some slack, so far as installation technique goes, and what they'll say about it. These backflow preventers get their 'legitimacy' by being approved by various agencies, like AWWA, ASSE, IAPMO, CSA (that's not the Confederate States of America) - and the testing is done on devices installed on the level. If a manufacturer wants an RPZ approved for use in a position other than horizontal, the device is tested separately, in another orientation (like vertically, with the flow downwards) ~ The extra testing costs extra money.

    Only with agency approvals, does a backflow preventer gain any 'street cred' ~ Even if the functionality of a PVB may exist no matter how it's positioned, it is only approved for the one position that the instructions describe.
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