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Old 10-10-2013, 04:23 AM   #1
Fusion916
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Default Can you install dual check valves underground for irrigation system?

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-Reduced-Pressure-Backflow-Preventer/dp/B001AS7C7U/ref=sr_1_fkmr1_1?s=hi&ie=UTF8&qid=1381377790&sr=1-1-fkmr1&keywords=Wilkins+3%2F4+inch+double+check+val ve

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.



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Old 10-10-2013, 12:13 PM   #2
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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)



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Old 10-10-2013, 03:11 PM   #3
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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?

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Old 10-10-2013, 06:20 PM   #4
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Quote:
Originally Posted by johnjh2o View Post
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)
Is a RPZ and double check the same except the pressure reduction? It looks the same:

http://www.amazon.com/Wilkins-Double-Check-Backflow-Preventer/dp/B0006B07A6/ref=sr_1_1?s=hi&ie=UTF8&qid=1381428926&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.
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Old 10-10-2013, 08:32 PM   #5
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This is a PVB. I'm sure you will find it is an approved device for your system.
http://www.amazon.com/s?ie=UTF8&page=1&rh=i%3Aaps%2Ck%3Apressure%20vacuu m%20breaker

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Old 10-10-2013, 08:45 PM   #6
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Given it is, does this also need to be elevated above ground? and if so, by how much?

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Old 10-12-2013, 04:58 AM   #7
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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.

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Old 10-13-2013, 07:13 AM   #8
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What is the difference between back siphonage and back pressure?

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Old 10-13-2013, 03:06 PM   #9
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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.

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Old 10-14-2013, 04:01 AM   #10
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Quote:
Originally Posted by Caduceus View Post
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.
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?


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