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Starting Member

Posts: 1

Location: USA


Monday, May 1st 2006, 10:23am

Backflow prevention

My sprinler system does not have a back flow preventer. I am told that without this my drinking water (well) can become contaminated.
Can anyone tell me what kind of preventor I need? Do I need one for each zone? Is there a code that i need to follow in NJ?


Supreme Member


Monday, May 1st 2006, 12:47pm

Can't help you on the codes for NJ.

As for which one you need, depends upon your particular situation. I can't even answer you question on "Do I need one for each zone?) I'd suggest you review has a whole section on back-flow prevention.

But just to get you started...

If you do one backflow per zone, that's where anti-siphon valves are used (i.e. if you don't already have these types of valves, to do one per zone requires the replacement of all your valves). However, anti-siphon valves can only be used if the valves are located ABOVE every sprinker head.

Simplar to anti-siphon valves are PVB. Only one is needed to protect the entire system and it's the cheapest alternative. However, the PVB must be positioned as the highest element in the entire irrigation system (i.e. once again, must be higher than all your sprinkler heads).

One of the next options is an RPZ (Reduced Pressure Zone). This is considered the ultimate in protection, but it has it's down sides too. It's the most expensive option. It comes at a cost of losing 10-15 psi available to the irrigation system. The RPZ must be installed above grade and outdoors (it must be allowed to spit out water to insure protection, and the "spitout" valve MUST NOT become submerged).

The other principal option is the DC (Double Check). This is basically a pair of double check valves with test cocks so insure it's properly working. But it's also considered the least protection. This is because in a critical failure, the device provides no protection, where as with an RPZ, a critcal failure usually results in lots of water comming out of the device and not back-flowing into your potable water supply. But it has the up side of much less pressure loss than an RPZ and because it doesn't have to vent anything, it can be installed below grade (i.e. in a valve box). Both RPZ and DC can be installed at any height relative to the rest of the system.

Hope that helps get you started.


Supreme Member

Posts: 5,288

Location: Metro NYC


Monday, May 1st 2006, 3:47pm

No Double Check Valve Assembly for New Jersey - the regional plumbing code for those Mid-Atlantic states requires toxic-rated devices. If you can cut it into the supply line, so that it's at least a foot-and-a-half higher than the highest head or pipe that it feeds, a PVB is the way to go. If you can't get that elevation difference, like when a property slopes uphill from the house, you must go with the RPZ, and deal with making the sprinklers work with the pressure loss.


New Member

Posts: 13

Location: USA


Wednesday, May 3rd 2006, 5:43am

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by HooKooDooKu</i>
<br />Can't help you on the codes for NJ.

This is because in a critical failure, the device provides no protection, where as with an RPZ, a critcal failure usually results in lots of water comming out of the device and not back-flowing into your potable water supply.
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">

Need help understanding, critical failure in the backflow device or in the sprinkler system? Next thing I need help with is, how does water get sucked backwards thru a control valve? If a control valve fails open - you see water passing thru to the sprinkler head. Do control valves fail in the closed position just enough so that when you use water in the house it creates enough vacuum to suck dirty water in from your sprinkler system? Wouldn't I notice air in my house water lines if that happened? I'm for backflow prevention, I just want to know more, yes I have read the tutorial from Jess. I do think of one example, if the water company had a break and had your water off, no backflow prevention on system, your controller opens valves to water, no pressure. Then would it run back into the house and the water main?


Supreme Member

Posts: 5,288

Location: Metro NYC


Wednesday, May 3rd 2006, 8:06am

Lawn sprinkler control valves have absolutely no way to prevent water from flowing backwards through them. They can only prevent normal 'forward' flow. Not backflow.

Go to your local library and read their copy of the National Standard Plumbing Code. There's even a special illustrated version for the non-plumbers out there.


Supreme Member


Wednesday, May 3rd 2006, 9:16am

<i>Need help understanding, critical failure in the backflow device</i>

An example of a critcal failure of a backflow would be if something got wedged into the device such that a check valve could not seal properly. In the case of a DC, you'll never know there is a problem with the device until you test it. In the mean time, you can get reverse flow through the DC. But with an RPZ, if the unit can not maintain the reduced pressure (i.e. if one of the check valves is failing) water will spit out the relifeve valve rather than allow the water to flow backwards.

And before you say "but my water is 'clean' city water, how could the devices fail". First, from experience I can tell you that I installed a fine mesh filter on my irrigation system. At the end of last year, I found a splinter of wood about the thickness of a toothpick and about 1/4" long trapped by the filter. When I reported this to Jess (basically to say thanks on his advice on filtration already paying for itself), I got back a reply something like this:
"It's amazing what you will find. I have found fish, tiny snails are very common and of course sand and pipe scale are almost a given."


Starting Member


Sunday, December 31st 2006, 7:54am

you definetly do not need one for each zone-one on the main branch is fine i would recommend febco 805y or conbraco should be within code


New Member

Posts: 4

Location: USA


Tuesday, January 9th 2007, 4:08am

Backflow advice/device:
I have an acre and 1/2 with a house in the middle, I want to irrigate the entire house with my well water. I am thinking about 10 zones with a PVB BACKFLOW device, what do you think? Or should I use 10 antisphon devices?



Supreme Member


Tuesday, January 9th 2007, 5:44am

Unless local codes require antisiphon valves, I would think it would be better to just use the one PVB. That way, you only have to have one thing sticking out of the ground to maintenance.

Then on the other side, if you don't care what's sticking out of the ground, and local codes don't required PVB (or higher end back flow devices), I would think having all the valves sticking out of the ground makes for easier maintenance of valves.

Of course the other thing to consider is slop of the land, because both PVB and antisiphon valves must be located higher than the highest sprinkler head.

And then of course if local zoning codes require RPZ, then you don't get to choose.

So for starters, find out what your local zoning ordanances are.

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