SPRINKLER TALK FORUM - You Got Questions, We've Got Answers

BTW, as for the irrigation valves, unless you are using valve with built-in AVB, the vertical location of the valves relative to the rest of the system doesn't matter (its a pressurized system).

(And for those that don't know what an AVB is, it's basically the same thing as an PVB. But where as a single PVB can be placed before all the irrigation valves, an AVB must be down-stream from the irrigation valves. Of course the way this works in reality is that you have what are know as in-line valves and Anti-siphon valve where the AVB is built into the valve, and the two valves cost about the same.)

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by DOORZ</i>
<br />Thats my problem; in order to get backflow 12" above the highest pipe, it has to be run 270' away from the meter, which just happens to be the highest spot on the property.

Will this hurt the system by having to add another 270' of pipe before even thinking about going to the first zone valve?
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You are either confusing yourself, or leaving out some essential information. Try to follow this example.

I have a three acre property that slopes very gently up from the house. The elevation of the ground at the house is five hundred feet. At some three hundred feet away from the house, the elevation is five hundred and six feet, and that is the highest point on the property. I install a pressure vacuum breaker at the house, tucked behind a chimney, for appearances sake, since it's over seven feet above gound level. The outlet of the PVB runs straight down to the ground, and everything else in the system is at or below grade. Since the elevation of the PVB is more than 507 feet, that provides protection for any in-ground sprinkler head or pipe, since they can be no higher than the highest elevation on the property, and that elevation is 506 feet, and that gives me the one foot minimum elevation difference that the PVB requires to be code compliant.

Only elevation matters. Horizontal distances are meaningless.

This example is for a sprinkler system fed from the house plumbing, where the ground slopes (slightly) uphill from the house. It is an extreme example, because a pro would really install a RPZ at a more convenient height, and deal with the resulting lower water pressure with more heads and zones (and more homeowner money)

For a similar system fed from a curbside water meter, there is no place to hide a very tall PVB, so the only realistic choice is an RPZ.

Well it looks like Toro has designed the system with the valve box at the top of the hill. I don't think that was done "because it's the top of the hill", but because that way you don't have to run every circuit back under the driveway. I think they also did it so that the control box is "hidden" on the far side of the property.

It seems to me the only way to stay within their 50psi diesign would be to use DC at the meter or a PVB at the top of the hill.

Using 1.25" PVC will only loss about 2psi on a 300' run.

If you are going to wait until spring to install this system, I'd once again suggest that you follow the instructions found a www.irrigationtutorials.com If you're waiting til spring, you've got time to study this site, and it will give you everything you need to make sure the Toro design is going to work. Yes it's a lot of information to go over, but better to determine if your plan is going to work BEFORE it gets put in the ground.

Virginia is probably not a state that will allow the use of a Double Check Valve Assembly, if they use the BOCA codes, so it's a PVB or an RPZ. The RPZ will cost you almost 10 psi more than a PVB, but that's just the way they're designed. If you have to have all the pressure possible, you can run the supply straight from the meter into the woods, then go straight up about eight feet and have the PVB at an elevation that is higher than any possible pipe or sprinkler head it will feed. And if you connect the system at the meter, you will want oversized pipe for the mainline, because your distances justify oversizing it this way.

If you feel inclined to repeat the thought about locating a backflow preventer at the point of highest ground elevation on the property, please hit yourself on the head with a hammer until the thought goes away.

<i>If you feel inclined to repeat the thought about locating a backflow preventer at the point of highest ground elevation on the property, please hit yourself on the head with a hammer until the thought goes away.</i>

Why is that? If a PVB is going to be used and there are no buildings or other objects to hide the fact that it's going to have to be stuck 7 feet in the air, why not place it on the up-hill side where it will only have to be 1' in the air? Add to that the fact that the design for this situation calls for the main line to pretty much run to the top of the hill anyway and I don't see what the big deal would be. The only change to the design I see that would be needed is to make sure the branching line running to the house is after the PVB, but that seems to add a minumum amount of extra pipe if the PVB is placed at the very top of the hill.

Can you elaborate on why you think the PVB should not be located at the top of the hill?

Water main in the street - water meter by the curb - sprinkler system connection - backflow preventer - sprinkler system

That's the the pathway taken by the water, and the distance between the first and the last is to be as short as physically possible. Especially if the sprinkler system pipe is going to be poly pipe (freezing climate you know) and the supply pipe into and out of the PVB is going to be copper tubing (the strongest and most durable choice)

The diagram indicates woods near the meter pit, and a possible 'hiding place' for a tall PVB. If there were no woods, you'd have an RPZ right near the meter pit, plain as day (or hidden under one of those hollow 'rocks' they make for the purpose) - I'd just go with the RPZ and live with the lower pressure, since I don't think it will affect the layout in the diagram.

The idea of running hundreds of feet of more-expensive-than-it-has-to-be pipe, just to aesthetically locate a PVB, is a non-starter.

Wet Boots, I still feel like I'm logically missing something (not trying to argue the point, just trying to get an understanding a learn something here). So please point out the flaw in the following logic:

Ignoring the branch line running to the house for a moment, it doesn't look like locating the backflow at the top or bottom of the hill is going to make a difference. The control valves are all located at the top of the hill, and you've got to have "expensive" mainline pipe on both sides of the backflow preventer. So place the backflow at the bottom of the hill or the top of the hill and you've still got to run 270' of mainline pipe.

Now taking the branch line into account, you are going to add 20' of mainline pipe and 40' to the total run for the water traveling to the house if you locate the backflow at the top of the hill. The water will have to run to the top of the hill, through the backflow, and then double-back for 20' to reach the point it would branch back towards the house. You can't argue "cost" says the backflow must be located at the bottom of the hill. If you attempt to use the least amount of pipe, you'd use an RPZ, but the cost difference in an RPZ and a PVB will makeup for the extra cost of the pipe. If you place a PVB 7' in the air at the bottom of the hill, you're going to use at least an extra 12' of pipe to go vertical, so now we're discussing a difference of 8' of pipe. Now in my opinion, the "cost" of 8' of pipe is worth the 10psi pressure difference, and the 10psi pressure difference more than makes up for the small amount of pressure loss the extra 40' water path is going to make.

So IF your priorities are in maximizing water pressure, the RPZ is out and your back to deciding is it better to have a PVB 7' or 1' in the air to choose top or bottom of the hill.

Now the one point that I will admit that your "shortest distance" argument would force the backflow to be at the bottom of the hill would be if you located the control valves at the bottom of the hill too. If that's what you've been driving at all along, you forgot to spell out that detail in this thread about what to do about backflow.

It might be that you are assuming I'd exactly follow the Toro design. I would not. I do my own designs. In a climate where the ground freezes, you would not be using PVC pipe installed in open trenches. You would be using polyethylene tubing installed by a vibratory plow, without digging trenches. In such an installation, connecting at a curbside water meter, the design would include a electric master valve to feed the mainline, just after the backflow preventer. The rest of the system could follow the Toro layout. (I would not group zone valves together, but locate them close to the heads they feed) By removing constant water pressure from the mainline, standard poly pipe can be used throughout the system, at a significant materials savings. That is why I emphasize a short path from water meter to sprinkler system.

I can see that my thoughts were heading in the direction that you laid out. I had thought of the idea of locating valves closer to the zones. But as a home owner, for athstetic reasons, I like the idea of grouped valves. Where I was really missing the boat was the idea of a master valve at the backflow.
Thanks for taking the time to relay your insights and experience.