Autofill hooked up to a sprinkler line

[Dirk]

Would the air gap that is built into the Pentair T40 with the Fluidmaster valve cover the backflow prevention needs? This is also assuming that the overflow is properly installed.

No, though it is a part of a good BFP system. A first line of defense. It’s missing two key components of a proper BFP. The bottom of it needs to be some number of inches above the highest level the pool water could ever get to, 6” to 18” depending on local code. Strike one. And it needs to be testable, and tested regularly. Strike two. The plastic those types of valves are made of are not really conducive to long-term reliable BFP...

 

[kingstar]

I’m not going to take any chances and will be using the one you suggested; however, I find it odd that this exact type of valve is acceptable for use in a toilet as a back flow preventer. But outdoor pool is a much harsher environment than the lightly chlorinated water in my toilet.

 

[Dirk]

I’m not going to take any chances and will be using the one you suggested; however, I find it odd that this exact type of valve is acceptable for use in a toilet as a back flow preventer. But outdoor pool is a much harsher environment than the lightly
chlorinated water in my toilet.

A few differences:

- The entire valve assembly in a toilet is well above "the potty water." It's basically submerged in clean, fresh water. The one in a pool is submerged in pool water.

- The outlet of the water supply line is [supposed to be] mounted above the tube that runs down to the bowl. So any water that is in the tank would overflow into the tube before it got near the open end of the supply line. If their was negative pressure in the supply line (like it was being sucked out into the street's main as I described), the end of the supply line is in the air, not in the water. That's the definition of "air gap." If your pool doesn't have an overflow system, or it got plugged up by leaves or something, the pool's water level could rise above the air gap built into the auto fill valve (if it even has one). In that scenario, negative pressure on valve could suck pool water into the street's main.

The household systems are not infallible, and are subject to failure. Which is why someday we'll all be required to have proper whole-house BFP.

If you use the BFP I suggested, and install it correctly (well above where any water could get near it), then you're good-to-go.

What I should have done is installed it on my water main, instead of just on the pool supply line...

 

[kingstar]

That makes sense. Thanks.

I'm going to install it above where the line exits my house, which is no where near any other sources of water and well above the pool water line.

 

[Dirk]

Bingo!

 

[Ironman92]

I don't have an auto-fill on my pool; however, I have a dedicated sprinkler zone for my pool fill. The zone is downstream of the back-flow preventer of the sprinkler system.

The sprinkler controller I used was the Rachio Wi-Fi controller. My PB replaced the old Rainbird controller with the Rachio and created a new zone to fill the pool when needed. He piped in the fill line from the sprinkler system during my pool build before pouring the deck.

I usually monitor the water level and add water as needed by dialing up the time on my phone app. For my pool, it takes about 18 minutes to raise the water level 1 inch, so I just play with the times when I'm adding water. Also, I can set up temporary schedules or fill the pool while I'm on vacation. Personally, I think this is better than manually adding water and waiting to shut off the valve (or forgetting to shut off the valve). I also didn't want an auto-fill because I was afraid that I would not notice a water leak for a long time.