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Backflow preventer

Posted by toffee1 9 (My Page) on
Sun, Aug 1, 10 at 17:19

I am planning to install irrigation for my house. I am can use anti siphon valves but prefer to use inline valves with some variety of backflow preventer. Questions:

1. If all my sprinkler, emitters etc are 6" below the level of backflow preventer, I can get away with using Pressure Vacuum Breaker. Is that true?

2. I would like it if I can run low pressure tubes to my 2nd floor balcony. By doing so, does it mean that neither anti siphon valves or pressure vacuum breakers would be sufficient? And I need something expensive like Reduced Pressure Type Backflow Preventer or a Double Check Type Backflow Preventer?

Thanks for reading and any help would be appreciated.

Follow-Up Postings:

RE: Backflow preventer

Hi Toffee,

Please provide your water source type of connection, pressure and flow rate. If you do not know how to obtain this info, I will help you.

An anti-siphon valve is essentially a vacuum breaker valve. They need to have the water level in the pipes below the valve to allow air back into the system to interrupt the back-siphoning when the irrigation stops. A check valve will block the backward flow of water mechanically. This is the type for your second story balcony because it will keep water in the pipes to the second floor balcony after water shut off. When you start irrigation again water won't have to be lifted again and you do not have to listen to all the air being pushed out of your emitters. Aloha

RE: Backflow preventer

Hi lehua13. Thanks for helping. My water pressure is about 60psi, 1" pipe from the city water company. I haven't check the flow rate.

I think this is what I will do.

I will run a water pipe to the 2nd floor balcony and install an anti siphon valve on the balcony. From the valve, low pressure hose will water the potted plants on the balcony. Of course I will make sure that valve is at least 6" above all the emitters.

I am wondering if I should install the pressure reducer (to 25psi) after the valve or install at ground level so the water travel up to the 2nd floor valve under low pressure hose?

Think my plan will work?

RE: Backflow preventer


What you have written is fine but the water in the pipe going up the line to the second floor could back into your house but it is such a minor amount and is not worth worrying about. Your valve at the ground level should act as backflow preventer unless it malfunctions. You will have plenty of pressure reaching the second floor(55 psi) and reduce the pressure on the 2nd floor to obtain your 25 psi. JMHO Aloha

RE: Backflow preventer

I have a situation very similar to Toffee1's. I want to add an additional drip line to the balcony from the existing irrigation system. The existing system has a shut off valve connected to the water supply. After the shut off valve is a pressure vacuum breaker (Wilkins model 720A) which then connects to 3 control valves (one for the lawn, one for trees, and one for shrubs). I simply made a new branch from the 1/2" black ploy tube off the shrub line to the foot of the house (about 10 ft). Then I plugged in 3 micro-tubes (1/4") into the poly tube and pulled them up to the balcony. Water pressure is good enough when it reaches the balcony. However now I just realized I will have about 10 drippers on the balcony. These drippers are located much higher than the Pressure Vacuum Breaker. I wonder how likely this is going to cause the PVB to malfunction. If I add an inline backflow preventer (you can buy it from Home Depot for just a few dollars) on the new poly tube will it solve the problem? I am looking forward to hearing from you experts :)

RE: Backflow preventer


I wouldn't worry too much about. The in-line BFP would just increase the friction lost to the drippers. As long as you don't have the drippers in the soil your good to go. If you have a break in the balcony line, the line would only suck air anyway. JMHO Aloha

RE: Backflow preventer

Hi lehua, thanks for your reply. Being an engineer I always think too much. I can certainly keep the drippers on the balcony off the soil. But my main concern was whether a few drippers on the balcony (higher than the PVB) would cause the entire PVB to fail when a backflow condition occurs, thus causing backflow from all other drippers (there are a lot of them and most of them are laying in the dirt). I have read a couple of articles about how PVB works but still don't have a definitive answer. Considering the low probability of backflow conditions, I think I should just concentrate on more important things in life and let this problem go. :)

RE: Backflow preventer


Yup. Aloha

RE: Backflow preventer

The solution for backflow is only the backflow prevention cage. We provide custom backflow cages with the safety issues as using by rounded edges. Provides extra durability and security in affordable price.
Contact us and let us know what your backflow preventers dimensions are and we will get to work on your custom cage.
Toll free : 877-490-7700
California - 949-903-3863
Arizona - 602-717-8017

Here is a link that might be useful: GuardianEnclousers

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