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

When the pipe needs repaired, you don't want to be destroying your wires while digging. Pipes on top of pipes? Only if you're a glutton for punishment. That practice can come back to haunt you. Especially when something breaks, with three or four other somethings on top of it.

If you are having wires in your trench, there is no reason you can't locate your zone valves right near the area they feed. One valve per location, each with their own mini valve box (they're cheap)

If you 'decentralize' your trenched system this way, it isn't likely you'll need more than one zone pipe running alongside a mainline.

Why the eighteen-inch mainline depth?

About the frostline, I wouldn't worry about it. Better to blow out all the water, come fall. Also better to use a RPZ at the point of connection, than to add hundreds of feet of pipe you don't need. Unless your supply pressure is less than 50 psi, you can live with the RPZ pressure drop. Sprinklers can run on 30 psi and survive. I know of one RPZ with a pressure drop of less than 10 psi. Not real cheap, but it's available.

What you contemplate is never done by professionals, so far as my own observations go, and they must have a reason.

This whole system-design question was beaten to death last summer.
http://www.sprinklertalk.com/forum/topic.asp?TOPIC_ID=1339

If you follow the Toro-supplied design, you are wasting money and materials. They probably assume you may be using a vibratory plow to install the lines. Go ahead and use their head locations, if you think they're okay, but find a different way to 'connect the dots'

By the way, do yourself a favor, and hire someone with a vibratory plow to install polyethylene tubing for this system. It will be worth the money you spend, if only for not damaging your lawn. And if you are dead set on using Toro's exact design, you could have a heavy-duty NSF-rated poly mainline, and not be risking too much in the way of future problems. You could also have PVC pulled as well, should you desire. Whatever pipe you use, it will all be cleared of water before winter, regardless of the depth it's installed at.

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by Wet_Boots</i>
Why the eighteen-inch mainline depth?
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">

Assuming DOORZ is using PVC, I though 18" was a CODE requirement for Mainlines.

<b>Multiple Pipes in the same trench</b>
I asked the same question my self last year because I too had a situation where I really NEEDED to place multiple pipes in the same trench.

The only answers I could find were:
1. Don't let the pipes touch each other.
2. The Pros don't do it from a stand point of maintainence.

What the pros are saying makes a lot of scence from the stand point of IF you ever have a problem with that bottom pipe, it will be a maintainence nightmare.

However, I'm not building my irrigation system with maintainence in mind, I'm building it to be as maintainence free as possible, so I decided to risk placing seven (7) pipes all in the same trench. I used the following justifications:
1. The pipes are all latteral lines (i.e. not under the constant pressure of the main line).
2. The pipes are all Schedule 40 PVC (over-kill for latterals).
3. I'm not just tossing the pipes in these trenches, I'm making sure the are resting on a bed of sand and/or screening all of the dirt that gets placed back into the trench next to the pipes (so all the large rocks are removed except for the top layers of the trench away from the pipes).
4. The minimum depth for the top pipe in the trench is still 12".
5. I live in the South where the frost line is like 1".

My only concern came when I found tree roots near the trench I was digging. My worry was that a tree root would grow between the pipes, swell up over the years, and finally break a pipe. So to help midigate that issue, I found some off-color vinyl siding on clearance and lined the side of the trench with it to try to keep the roots out.

From what research I did on the subject last year, there's nothing in the plumbing code about it (there's on details on the location of sewage pipes and water source pipes in the same trench.


Given that you are wanting to place
So it basically comes down to the risk you want to take for any future repairs.

The one piece of advice I can give you from my experience is that the pipes will eat up more space in those trenches then you think. I dug down 24" deep to install 4 levels of pipe: 1 1" pipe on level 1, 2 1" pipes on level 2, 2 3/4" pipes on level 3, and 2 3/4" pipes on level 4. My pipes are rediculously close together and the top level tops out around 12" - 10" deep.

Another note, is that in a 4" wide trench (when dug by a typcial ditch witch) will only leave about 3/4" to 1" of space between two 1" PVC pipes places in the same trench beside each other.

So basically, if you do multiple pipes (specifically 6) in one trench, you either gamble that you'll never have to "fix" any of these pipes, or you get a ditch witch that can dig a 6" wide trench and make a trench 6" x 24" to place your 6 pipes... wait, make that 26" to 28" to make room for your wire.

There is no particular code requirement for the depth of a seasonal waterline, mainline or no. I question the wisdom of trenching that deep, because of the increased chance of hitting some underground utility. Better to work within a foot of the surface, and stay out of trouble. If I were a strict local official, I would maybe insist on thick copper tubing between the connection at the water meter and the backflow preventer. A requirement like that would make an RPZ near the meter the way to go, because the price of the copper tubing is too high to go installing hundreds of feet of it.

I made a printout of your Toro-supplied design, and looked it over with a ruler in hand. It looks like you have square spacing, more or less, with 30 feet or so of spray radius from your rotor heads. Even if it's a 40 foot radius on the drawing, the following analysis would apply.

You don't need so many zones. With Hunter PGP's, I could almost certainly cover the front strip in three zones. The rest could be handled with two more zones. One for rotors and one for spray heads. And this with a RPZ near the meter. If it were possible to run a supply line into the woods, and make a camouflaged install of a tall-enough PVB, there would be even more pressure available.

I would make the RPZ connection first, and then make some flow-and-pressure measurements at the source. That's a way to be conservative, and make certain of your water supply. You may have a lot more available flow than the Toro design makes use of. With head to head spacing, you don't need much pressure. If you do have good flow at, say, 40 psi, downstream of the RPZ, then you can be assured of 30 psi at the heads. That's plenty. With the possible addition of a head or two, you might even do well with 25 psi at the heads. In some cases, one can even do a system with as little as 20 psi at the heads, although you start getting into some obscure equipment.

The flow test would also tell you if it would make sense to bump up the size of your mainline to inch-and-a-half. Depending on your results, the increase would be a way to conserve pressure.

If you wanted to be really conservative, you could make your connection at the meter, and do flow-and-pressure tests right there, and have the information on what your supply really is. Those numbers would help you work out the other details.

I think your design way underestimates the amount of water that a one inch meter will supply. Go ahead and tee off after the meter, and run some water through the new connection. Use the meter and your wristwatch to calculate the flow rates. Put some one inch pipe with a pressure gauge on it, and a valve at the end, so you can try different flows, by adjusting that valve. You have the luxury of being able to do this one step at a time. And you don't really have the experience and expertise to evaluate your water supply in any other way. If you don't have the information on the PGP performance, with all the various nozzles that it uses, get the information. (at low pressures, like what you'll have, it's nozzle sizes #1 through #6 that will get used most)

Just make the connection, or you may become a victim of 'paralysis by analysis' ~ at some point, you have to make a start, and the connection is the way to begin.