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Advanced Member


Thursday, April 27th 2006, 4:55am


I am planning on renting a trencher to install my pipe. I have an area that is 30' wide X 270' long and was wondering if it's alright to lay different zones in the same trench. The entire area will require 5 zones.

I have to cut a trench down the entire length to run the mainline and to also get to other areas in the yard. Since the mainline needs to be buried 18" deep, I was hoping to be able to bury the mainline throw some dirt ontop of that & then put my latterals on top of that at 10-12" deep. Since I assume all 5 zones along with the mainline wont fit in the same trench I would have to dig another along side this one to put the remaining zones that wouldn't fit in the first trench.

Is there anything wrong with doing this with the mainline & laterals? It would save alot of trenching in this area if I can.

And in reading the irrigation tutorial, it mentions The wire should be at least two inches away from the pipe, and either next to, or under the pipe. I can understand running it under the pipe, but why 2" away?


Supreme Member

Posts: 5,307

Location: Metro NYC


Thursday, April 27th 2006, 6:08am

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?


Advanced Member


Thursday, April 27th 2006, 6:50am

I was hoping to combine some of my pipes in the same trench which is why I asked.

The water meter is at the low point on the property (at one end of my 270' strip), and I need to run a mainline up to the high point (the other end) to install my PVB and also to be able to get to the areas in the front yard as well as the back. I am running the mainline 18" deep to stay below the frostline.

Since I have 5 zones and the zone valves are being installed at the high spot after the PVB I am starting at the high end and work back to the low end. If I dig a trench to each zone the first one will be about 70', the next 133', the next 170' and the last 235'. Since my mainline goes the entire length that's why I was looking to combine pipes in the same trench.

The other areas in my yard are much easier, since the mainline will be brought right up to the area to be irrigated, and I will install a zone valve right there. If it's a REALLY bad idea to combine pipes in the same trench, then I will have to avoid doing so.

I had looked at using a reduced pressure assembly, but due to the inceased pressure drop it cuts the system too close.

The only area I was planning on running wires in the trench were where the mainline is. The mainline passes by the end of the house, so running the wires in the mainline trench would be a convienent place to run the wires to get to the zone valves. The irrigation tutorial says to keep the wires at least 2" away from the pipe, and I was wondering why this is? I understand wanting to run it under the pipe due to diging, and keeping it under the pipe would protect the wires, but why 2" away?


Supreme Member

Posts: 5,307

Location: Metro NYC


Thursday, April 27th 2006, 7:20am

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.

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.


Advanced Member


Thursday, April 27th 2006, 9:37am

I obviously missed a lot end responses that were posted last summer.

I went back and looked at my pressure loss table I created using the irrigation tutorial. If I figure things based on that table, I am a 1/2 PSI below my design pressure of 57 PSI using a RPZ. Do you think I am safe in working with this?

When I initially did the pressure loss table I was VERY conservative, and overestimated some of the PSI losses to be on the safe side, and adding the RPZ would have put me over my design pressure by 1-1/2 PSI.


Supreme Member


Thursday, April 27th 2006, 12:58pm

<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.


Supreme Member

Posts: 5,307

Location: Metro NYC


Thursday, April 27th 2006, 3:15pm

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.


Advanced Member


Friday, April 28th 2006, 3:59am

Thanks for all of your input <b>Wet Boots</b>.

I have re-worked the system incorporating a RPZ. Irronically before seeing your post last night I had thought about changing my mainline to 1-1/2" due to the mainline having to run 380'. Doing this would gain me another 1.3 psi in the sysyem, which I figure would be better.

Also by using the RPZ I was able to reduce the amount of piping in zones 9-13 since I am able to come right off the mainline and did as you suggested and installed the valves right next to the zone.

The previous layout as well as my current layout was based on rotors at 30' spacing. You mention I would be able to able to cover the front strip in 3 zones with PGP's. How would I be able to do this with PGP rotors verses other rotors?

With a static pressure of 57, I should have more than 40psi after the RPZ, since it looses 12psi. I had figured between the loss of mains, laterals, valves 30psi at heads, etc. that after adding it all up I was really close to my design pressure.

I have provided a link to my new layout, let me know if you think this looks better than the first layout.

Zone 3 - drip
Zones 4,5,6 are sray heads
Everything else rotors


Supreme Member

Posts: 5,307

Location: Metro NYC


Friday, April 28th 2006, 4:48am

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.


Advanced Member


Friday, April 28th 2006, 5:14am

Thanks for all of your help

By the way I am only working through a 3/4" meter, and not a 1"

I guess it does become an matter of over analyzing the situation sometimes. I am the kind of person who likes to do things myself, and do as much research as I can so I get a full understanding of what I am getting into, which is the reason for asking all the questions.

I had looked at the PGP rotors, and did post a question asking about the flow rates. It seemed very strage to me that the flow rate on the PGP standard nozzles were so much lower than other rotors (even PGP with gray nozzle), and I didn't understand why this was. Never got a good explanation on this, only thing I can figure is that Hunter did this due to situations like mine where you don't have high flow rates.

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