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ericnash

Unregistered

1

Friday, July 26th 2013, 7:56am

Placement of Pressure Vacuum Backflow Device

Hello, I'm installing a sprinkler system in my backyard. The yard is on a slight slope, with the higest point about 4 feet higher than my water supply line. (The 4 feet slope goes over about 70 feet.)
I am pulling the water off a hose bib that comes out of the house. I was hoping to have the anti-siphon valves near the house as that is where my electrical is.
Since there is a slope, when the sprinklers turn off, the water in the pipes will fall back into the anti-siphon valves.
My questions are:

1) I wasnt planning on using a pressure vaccum breaker device. Do I need to or will the anti-siphon valves work?
2) If I do need to install a PVB, is there a specific location that it needs to be? Can I place it close to the anti-siphon valves?
3) Would it be easier to move the anti-siphon values up to higher ground? And if so, where would I install the PVB - near the water source by the house or by the anti-siphon valves?
It seems like the best solution would be to place the PVB right by the house and then place the anti-siphon valves uphill.
I apprecaite any help and suggestions! Thanks!
Eric

Ken D

Unregistered

2

Thursday, August 29th 2013, 1:50am

PVB Placement with ASVs

Hi Eric,

Only one type of backflow prevention is required, so there is no reason to install a PVB with ASVs. However, neither of these will provide protection unless they are installed 6" above your highest head (or pipe). Note that code in some areas require this to be 12 or even 18". ASVs are just valves with an atmospheric vacuum breaker (AVB). AVBs are available separately, but one is required after each valve, and no other valves can be downstream of the AVB. PVBs can have valves downstream, so if used, you only need one, and then you could use remote control valves downstream that do not have backflow prevention (are not ASVs). These could be installed in valve boxes. However, in some areas, PVBs have to be close to the point of connection (POC). I would not recommend a PVB if you have a pump, as they do not protect from backpressure.

Reduced pressure principal assemblies (RPs) are installed 12" above grade, but can be installed below sprinklers and pipes. They are expensive and typically have to be certified annually. You could install one of these at your POC and then valves anywhere downstream. I would check on the certification requirements before installing. This is going to be an expensive solution and only rarely done on residential irrigation systems. If you are going to consider this, check on certification requirements and manufacture spec's for other requirements (freeze protection, clear space for testing, drainage, etc.)

I do not recommend double check backflow preventers, and most areas do not allow them for irrigation backflow prevention anyway.

So, it seems you have three solutions:
  1. Install the ASVs at a location at least 6" above the highest head (or pipe). Least expensive solution.
  2. If you don't have a pump, Install one PVB at a location at least 6" above the highest head (or pipe) and then run mainline to install remote control valves where you want them, and they could be in valve boxes.
  3. Whip out the credit card and install an RP by your POC and then run mainline to install remote control valves where you want them, and they could be in valve boxes. Most expensive solution.
Check your local requirements before selecting #2 or 3, as noted above.


I hope this helps.

Ken

Wet_Boots

Supreme Member

Posts: 4,030

Location: Metro NYC

3

Thursday, August 29th 2013, 5:29am

Actually, a PVB has to be 12 inches (not measured from the top of the PVB, but rather the outlet pipe) higher than any pipe or head that it feeds. I would install a PVB so that its top was at least two feet higher than downstream pipe or heads.

hi.todd

Supreme Member

Posts: 413

Location: Houston, Texas

4

Thursday, August 29th 2013, 9:00pm

Yes, PVB 12" above all piping and heads. Atmospheric Vacuum Breaker is 6", but not OK for constant pressure.

I am alive!

The PVB and RP Both need to be certified annually.

The RP is not as stable on a pump as the water source as the PVB. The RP will lose 10.0 LBS of Pressure, and the PVB will loose 2 or 3 LBS of Pressure.
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