backflow prevention valve

[Mighty_P]

Hey TFP,

I had an automatic water filler installed, and had a different guy run the water line for me a few months ago. He put in 2 manual valves, one right before the pool and one on the other end near the water supply. This is nice because I can seal it off from either end. But, he did not install an anti-siphon valve to prevent water from being sucked from the pool back into our house lines. I'm not clear exactly what is needed...is the attached photo the proper product for this?

cheers!

 

[mknauss]

Back Flow Preventer - Further Reading

www.troublefreepool.com

 

[Ahultin]

is the attached photo the proper product for this?

Nope that does not offer any backflow prevention

I'm not clear exactly what is needed.

Depends on what area of California you are in. In many counties these are installed and meet code :
Zurn Wilkins 34-720A 3/4" 720A Pressure Vacuum Breaker Assembly Amazon.com
Where I am in San Diego county unincorporated, this was required AND has to be tested annually:
Wilkins 34-975XL2 3/4-Inch Reduced Pressure Backflow Preventer Amazon.com

 

[1poolman1]

Hey TFP,

I had an automatic water filler installed, and had a different guy run the water line for me a few months ago. He put in 2 manual valves, one right before the pool and one on the other end near the water supply. This is nice because I can seal it off from either end. But, he did not install an anti-siphon valve to prevent water from being sucked from the pool back into our house lines. I'm not clear exactly what is needed...is the attached photo the proper product for this?

cheers!

What part of California? In my area a standard anti-siphon sprinkler valve has always been accepted. Picture is the same brand as found at Home Depot.

 

[Ahultin]

In my area a standard anti-siphon sprinkler valve has always been accepted. Picture is the same brand as found at Home Depot.

I could be wrong, but as I recall, @Dirk had stated that those sprinkler valves are not rated to have an additional valve (like the autofill) downstream of them

 

[1poolman1]

I could be wrong, but as I recall, @Dirk had stated that those sprinkler valves are not rated to have an additional valve (like the autofill) downstream of them

Rated? Don't know. Seen virtually everywhere in Sacramento even with autofill? Yes.

 

[Dirk]

those sprinkler valves are not rated to have an additional valve (like the autofill) downstream of them

You are correct, sir!

Code and requirements and "accepted" aside, a sprinkler anti-siphon valve is not the correct thing to use if there is any kind of valve downstream of it, including any sort of secondary shut off valve, or the auto-fill mechanism itself (which is a valve).

Sprinkler anti-siphon valves have a spring and diaphragm that do the "anti-siphoning." That is a type of backflow prevention, so technically a sprinkler anti-siphon valve is a backflow preventer (BFP). The problem is, the spring in a typical sprinkler anti-siphon valve is of a "strength" and quality that is expecting to deliver water to a set of sprinklers. Because the water is always flowing out of the sprinklers, the pressure on the spring will be significantly less than the full pressure available (coming from the street). Further, sprinklers are typically run a few minutes a day, so when the circuits are done watering, all the water drains out through the sprinklers, and then there is zero pressure on the anti-siphon parts. So these cheapie Lowes valves have springs that can only handle reduced pressure for a few minutes a day (so that they can sell them for 20 bucks).

Now when you add a second valve downstream of one of those, and that second valve is closed (either because you closed it, or the pool is full and the auto-fill valve closes itself), there is now nowhere for the water to flow, and so the pressure builds in the output side of that sprinkler anti-siphon valve, all the way up to the full pressure coming into that valve (typically the same pressure as the street pressure, which can be much higher than the pressure on valves inside your home). Worse still, that pressure is now trapped in the pipe between the sprinkler anti-siphon valve and the secondary valve downstream, 24-7. The only time the pressure gets reduced, is when the pool needs a little water. Which might be only a few minutes a day. Once the pool is full, the pressure in that pipe returns to full-on!

So now all that pressure is pushing on that poor, cheap spring and diaphragm, all the time, and that's what we mean by "not rated." That spring is not designed (rated) to push against that much pressure all day every day. Eventually the spring and/or the diaphragm will poop out, and you'll either get a leak, or worse, it'll just stop functioning as a backflow preventer. But because those cheap valves don't offer any way to test them, you may never know if or when that "anti-siphon" backflow preventer is no longer capable of preventing anything.

Whew! So... what you get when you get a properly rated BFP, is one that has stronger springs and diaphragms, plus test ports that allow it to be tested periodically.

So while inspectors might look the other way (or not understand what I just described) and/or a cheap sprinkler anti-siphon valve might work for years, that doesn't mean it's OK to use for this purpose.

 

[Mighty_P]

Thanks for the info, everyone! One other question...does it matter where on the line it's installed? Should it be closer to pool, or closer to water source? Or in the middle?

 

[Ahultin]

Mine is installed at the pad . As it is intended to protect your potable water in the house, Ideally you want it installed as early as possible on the line.

 

[Dirk]

Backflow prevention is not really intended to keep pool water out of your house, though it can also do that. Backflow prevention keeps all of your water (pool water, toilet water, water in your garden hoses, or in your washing machine or dishwasher, etc) out of the city's water supply.

Backflow can occur during a backflow event. Here's the example I described in the Further Reading article that Marty linked:

Accidental events (like a broken water main, for example) can create a situation where water is sucked out of a contaminated source on an individual's property, back out into the public's common water source (the water main). Later, when the main is repaired, the contaminated water gets pushed back into all the surrounding houses! The contaminated source might be a pool, or a hose filling a bucket of nasty garden chemicals, or a hose laying in a muddy garden, an improperly installed water filter or water softener, etc. A BFP keeps any water from your property from entering the public's, or a well.

Things in your house already have built in BFPs: there's one in each of your toilets, a properly installed dishwasher has one, etc. So your pool needs one, too. As long as it is somewhere between your auto-fill valve and the city's water supply, it can do its primary job. Now, if you have your pool fill source coming from a water softener, or perhaps a hose bibb pipe, it's possible a street-wide backflow event could drag some pool water through some of the plumbing in your house, so ideally it should be between the autofill valve and wherever the pipe feeding it exits your house or garden.

The height above the pool water surface is really the more important thing you need to satisfy, so install it where its height above ground is the least intrusive to your yard and walkways. As @Ahultin suggests, on or near your pool pad is a logical choice. That's where mine is.

 

[Ahultin]

Backflow prevention is not really intended to keep pool water out of your house

Good info - in my case though being county of San diego, that's really all it does.
I have an existing 2" rpz immediately following the water meter that we were required to install when we built the house to protect the city supply. In 2020 when we added irrigation I was required to place a 1" rpz after the line split off the house supply before the irrigation valves. Then in 2021 when we added the pool another 3/4" rpz was required for the pool (I had an easy way to tee off after the 1" irrigation rpz thinking it would save money but the county said that was also not allowed.

 

[Dirk]

Good info - in my case though being county of San diego, that's really all it does.
I have an existing 2" rpz immediately following the water meter that we were required to install when we built the house to protect the city supply. In 2020 when we added irrigation I was required to place a 1" rpz after the line split off the house supply before the irrigation valves. Then in 2021 when we added the pool another 3/4" rpz was required for the pool (I had an easy way to tee off after the 1" irrigation rpz thinking it would save money but the county said that was also not allowed.

Yah, that sounds like city lawyers got involved. It's a combo of common sense, science and litigation results that drives building codes.

Mine used to be on a branch split off underground before the house, on the city side of my house's pressure reducer. The auto-fill line was taken off the irrigation plumbing, like you wanted to do. So a backflow event from the street wouldn't have sucked pool water into the house, but rather drained both the house and the pool together. And since the pool is below the house, the water wouldn't have traveled "up." The pool builder did put a cheap check valve on the auto-fill line, and that must have passed inspection (before I owned the property).

My city doesn't require an RPZ between property and street, so we don't even have that protection. So, yah, every city is going to have different requirements, and the OP probably needs to investigate and meet those, if for no other reason than to stay compliant.

Then I really messed things up by rerouting my auto-fill supply to my indoor circuit, to fill the pool with soft water. That's when I installed the BFP, just in case. Later, I re-did my irrigation, so installed one there, too. But there's still nothing between my house and the street!

My city-water-company-employee buddy, who taught me all this stuff, thinks eventually, here in CA anyway, BFP will be required everywhere. Currently it's required on all businesses, just not residences. He figures they'll start with new construction, and then maybe someday require retrofits for everyone. Typical indoor fixtures have built-in BFP, as I mentioned, so that's probably why this has never been addressed, nation-wide. But that doesn't account for numbskulls like me that modify their own plumbing. Or pool builders or landscapers that take shortcuts that never get inspected.

So while all that BFP is a pain for folks like you in forward-thinking cities like yours, it really should have been mandatory ions ago, everywhere. Ultimately, you and your family and your neighbors are safer, and while shelling out for that was no fun, you can feel good about contributing.