# Irrigation Question What is this thing? **URL:** \ **Category:** Factual Questions\ **Created:** [January 30, 2012, 12:36am UTC](https://boards.straightdope.com/t/irrigation-question-what-is-this-thing/611129 "2012-01-30T00:36:53Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![obbn](https://avatars.discourse-cdn.com/v4/letter/o/d6d6ee/32.png) [@obbn](https://boards.straightdope.com/u/obbn)\ **Post date:** [January 30, 2012, 12:36am UTC](https://boards.straightdope.com/t/irrigation-question-what-is-this-thing/611129/1 "2012-01-30T00:36:53Z")
Hello All, I am having a problem with my irrigation system. The county is testing backflow prevention devices. I believe that mine is working properly but it cannot be tested because when I turn the water main on to provide water to the irrigation system this “device” starts leaking water from what looks like a o-ring possibly on the top of this device. The part that is leaking is at the top of the device and it looks like a big round knob or cap. It’s the one on the left in the picture with the raised “ridges” around the side. To make a long story short, the water guy from the county told me I didn’t need that part and his suggestion was to “cut it off” and just put in a few 90 degree pieces to close up the pipes. I don’t know if this is correct or not because I don’t know what the damn thing is and does and he didn’t really explain it all that well. So, does anyone know what it is? Can I fix it with a new o-ring or something or would his advice of “just cut if off” be the best and easiest way to go. Thanks in advance for your help. Pic [https://picasaweb.google.com/lh/photo/ZEkM-UcE\_9VtG842OpYlG691DwRvJdANZoSrW8yteMM?feat=directlink](https://picasaweb.google.com/lh/photo/ZEkM-UcE_9VtG842OpYlG691DwRvJdANZoSrW8yteMM?feat=directlink) ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [January 30, 2012, 1:14am UTC](https://boards.straightdope.com/t/irrigation-question-what-is-this-thing/611129/2 "2012-01-30T01:14:56Z")
That’s your back-flow preventer. It may unscrew, and allow you to clean it. It’s also possible that you have an obstruction downstream. ---
**Author:** ![obbn](https://avatars.discourse-cdn.com/v4/letter/o/d6d6ee/32.png) [@obbn](https://boards.straightdope.com/u/obbn)\ **Post date:** [January 30, 2012, 1:21am UTC](https://boards.straightdope.com/t/irrigation-question-what-is-this-thing/611129/3 "2012-01-30T01:21:01Z")
> [@beowulff](#): > > That’s your back-flow preventer. It may unscrew, and allow you to clean it. It’s also possible that you have an obstruction downstream. The guy from the Water Department told me that it wasn’t the backflow preventer, in fact he told me to cut it off! There is another device installed before this one that is certainly a backflow preventer. It looks just like this: [http://www.google.com/products/catalog?q=backflow+preventer&um=1&ie=UTF-8&tbm=shop&cid=5826972170067627446&sa=X&ei=FPAlT8PWB-n10gGr\_pDqCA&ved=0CI0BEPMCMAI](http://www.google.com/products/catalog?q=backflow+preventer&um=1&ie=UTF-8&tbm=shop&cid=5826972170067627446&sa=X&ei=FPAlT8PWB-n10gGr_pDqCA&ved=0CI0BEPMCMAI) Would there be two of the backflow devices mounted for any reason? Oh, and FWIW, we don’t use the sprinklers since grass doesn’t seem to grow in this part of Florida. The water valve is always shut off that supplies water to the irrigation system, so it isn’t a daily problem. However the backflow preventer must be tested to meet local requirements. ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [January 30, 2012, 1:44am UTC](https://boards.straightdope.com/t/irrigation-question-what-is-this-thing/611129/4 "2012-01-30T01:44:33Z")
Strictly speaking, it’s an anti-syphon device, but everywhere I’ve lived they are required to prevent backflow: > [@](#): > > Anti-Siphon Valves > Anti-siphon valves are an inexpensive choice and easy to install and maintain. The built-in anti-siphon backflow device prevents potential contamination of household wa- ter supplies from fertilizers and other toxic chemicals which may enter the system. Check your local codes for the types of backflow protection required in your area. Electric models are simple to hook up to a timer for automatic watering. They are best suited to plans where there is not more than a slight rise in elevation, and fairly clean source water. (From Rainbird) ---
**Author:** ![obbn](https://avatars.discourse-cdn.com/v4/letter/o/d6d6ee/32.png) [@obbn](https://boards.straightdope.com/u/obbn)\ **Post date:** [January 30, 2012, 2:05am UTC](https://boards.straightdope.com/t/irrigation-question-what-is-this-thing/611129/5 "2012-01-30T02:05:10Z")
> [@beowulff](#): > > Strictly speaking, it’s an anti-syphon device, but everywhere I’ve lived they are required to prevent backflow: > (From Rainbird) Thanks, I will see tomorrow if I can get it to unscrew and see if there is dirt in the o-ring or something. Possibly my local sprinkler company will sell a replacement o-ring. ---
**Author:** ![thelabdude](https://avatars.discourse-cdn.com/v4/letter/t/dc4da7/32.png) [@thelabdude](https://boards.straightdope.com/u/thelabdude)\ **Post date:** [January 30, 2012, 2:44am UTC](https://boards.straightdope.com/t/irrigation-question-what-is-this-thing/611129/6 "2012-01-30T02:44:09Z")
> [@beowulff](#): > > Strictly speaking, it’s an anti-syphon device, but everywhere I’ve lived they are required to prevent backflow: > (From Rainbird) I agree, an older device also know as a vacuum breaker that allows air in to preven water being sucked back through it. I think a properly working one would be less effective than the widely required backflow preventers. I agree with the inspector, chop it out if you can’t repair it. ---
**Author:** ![Snnipe\_70E](https://avatars.discourse-cdn.com/v4/letter/s/b5a626/32.png) [@Snnipe\_70E](https://boards.straightdope.com/u/Snnipe_70E)\ **Post date:** [January 30, 2012, 2:46am UTC](https://boards.straightdope.com/t/irrigation-question-what-is-this-thing/611129/7 "2012-01-30T02:46:06Z")
It is not a back flow device. It is a vacuum breaker- anti-syphon device. It does not have to pass inspection. I would leave it after repairing. ---
**Author:** ![Dag\_Otto](https://avatars.discourse-cdn.com/v4/letter/d/439d5e/32.png) [@Dag\_Otto](https://boards.straightdope.com/u/Dag_Otto)\ **Post date:** [January 30, 2012, 6:21am UTC](https://boards.straightdope.com/t/irrigation-question-what-is-this-thing/611129/8 "2012-01-30T06:21:16Z")
Well, technically it is a backflow device (it’s an atmospheric vacuum breaker, and there is nothing to test), but it is not required as you have a reduced pressure device upstream. However, the reduced pressure device is a testable device, and required calibrated gauges to test properly. If the county tests this for free, then good news for you.