Another Sprinkler System Question

[JR]

Take my word for it guys... I do know just a little about this.

This is do not doubt!

Now you've got me rethinking my design. If I have to spend another month of weekends on this project I will kill you - then thank you!

JR

edit: It now occurs to me that I have an anti-siphon valve at the top of the run feeding the line on top of my slope.

[crokett]

edit: It now occurs to me that I have an anti-siphon valve at the top of the run feeding the line on top of my slope.

Got a pic? Is it up out of the ground? I could get away with putting one in my flower bed, but not out in the middle of my yard.

[Uncle Cracker]

If you use valves with an AVB, you can put them anywhere you want. If you use separate AVB's rather than built-ins, there must be one on every sprinkler zone, and it can be located anywhere between the zone valve and the first sprinkler downstream of that valve. With other types of backflow preventers, you only need one in your mainline, and it must be located between your service connection and the first zone valve downstream of that point.

I am not totally convinced that JR has an anti-siphon device on that elevated zone. He may have a simple check valve, to hold the water up on the hill, instead of allowing it to drain back to the bottom. That is not the same as a true backflow preventer. It is a practice not uncommon on sites with differing elevations. But it's not about public health when used that way. It's about preventing head drainage at low points, and about avoiding large influxes of air into the lines through the higher heads when the water drains back into the system.

[crokett]

Cracker, is what you are calling an AVB different from this?

http://www.irrigationtutorials.com/sprinkler10.htm

He says the AVB (with antisiphon) has to be installed above the highest sprinkler head on the zone. I think I am going go with either the RP backflow or the doublecheck. The RPZ needs to be installed above grade, but not necessarily higher than the sprinkler. The double backflow can be installed anywhere. If I could get valves that were BFPs without needing to be installed obove the sprinkler heads, that would be ideal.

[Uncle Cracker]

"AVB" means "Atmospheric Vacuum Breaker". It is the simplest type of backflow preventer. Also the least accepted by authorities. Not rated for installation in a constantly pressurized line, they are installed downstream of each zone control valve (or, as in your diagram, as an actual part of the zone control valve).

Of your other listed choices, try for the double-check first. It is cheaper than the RP, and can be located in your basement without regard to elevation. It also won't have the potential to vent water into your basement, as it has no air vent. Lastly, it will cost you far less pressure than an RP. RP's are designed to work on the principle that water will not flow from an area of lower pressure to an area of higher pressure, so a differential zone is set up which will cost you from 12-15 psi, which is tough to swallow on many systems.

The only problem with a double-check device is that it has a lower hazard rating than an RP, and is therefore not accepted in many jurisdictions. Check with your code-enforcement folks. If they accept it, you should use it. Remember, double-check is different than dual-check. Make sure you get a double-check device.

AVB's are the only backflow prevention devices that you can get built-in on your electric valves. There are no built-in DCVs or RPs, so you can abandon that option.