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Running water lines for a big garden

 
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I'm working rapidly on plans to trench water for a community garden in a few days.  We need to connect up to a city meter that isn't in place yet (I'm calling about that in the morning).  From there we'll need to trench about 200 feet to the first spigot location.  From there we need to tee/split off to 6 other spots.  We're in Wisconsin so it gets cold.  The city will remove the meter in the fall and reinstall in the spring.  I'm trying to figure out a bunch of details so that we can do this semi-correctly.  Here's my first raft of questions for the experts out there

1.  We do get frost but this site will generally be snow covered so I doubt frost will get very deep.  We'll ideally be able to drain the system mostly.  Am I correct in thinking that black poly pipe 18" deep would be a reasonable plan of attack?  The lines will run under lawn and under the garden plots.  I doubt any gardener will do anything deeper than 12" and we can run that section inside a larger metal pipe for protection if it's really warranted.

2.  The site is quite flat so we can't rely on a slope for drainage.  If we eyeball the low end and put a drain valve 18" down in an accessible pit, would that be a good approach to draining?  Open the spigots and let it all drain to one end?

3.  What size lines should we use?  I'm thinking 1" for the main feed and branches and then 3/4 going up each post to the spigots?  

4.  Is barbed plastic fittings and SS hose clamps good enough for the joints?  I'm not familiar with PEX hardware and tools...

Thanks!!!
Water-main-is-off-the-top-center-of-the-page.-Supply-run-will-travel-to-the-water-spigots-label-and-then-to-the-rest-of-the-spots.jpg
Water main is off the top center of the page. Supply run will travel to the water spigots label and then to the rest of the spots
Water main is off the top center of the page. Supply run will travel to the water spigots label and then to the rest of the spots
 
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Mike,

Ask around about the depth of those lines. I am far south of you, and I go for 18".  Even then, my hardware store recommends 24.

I have no idea as to acreage or your exact location with respect to city limits.   That said, have you looked into getting a well? If you are where a sand point can be used, you could see significant savings.  Such things are tricky, but it is worth considering.
 
Mike Haasl
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Thanks John, our official frost depth for foundations is 4'.  But these lines would be drained so I think it's a different situation.  Getting water to the site is pretty easy, power for a sand point would be harder.  Plus the city will be good to work with and it should be under $250 per year.  
 
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1. Depth: Buried lines are notorious for working their way upwards. If you want them to stay at 18", bury them at 24".

2. Drainage: Yes, try to add some slope and have a low drain point. But gravity drainage is not enough. Also plan for a way to hit each leg with good volumes of compressed air. Assume you will have low spots where water will fill the line and burst when it freezes. Finding a leak in buried pipe is a royal pain.

3. Pipe size: Go big, young man. It's not about pressure, it's about volume. I would suggest 1-1/2 for the main supply line. 3/4 is okay for the legs.

4. Fittings: Yep, barbed connectors and clamps will work fine. If assembling while cold, pour near-boiling water on the poly hose to soften and get a better seal when you clamp it down. Some use a propane torch, but I've heard it can cause weakness in the pipe.

5. Luck! Great project.
 
Mike Haasl
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Thanks Douglas!  Ok, we'll go bigger on the main runs.  

I really suspect we won't have frost getting that deep (due to snow cover).  My main worry is pitch forks and trellis stakes.  I did put black poly pipe in my home garden a few inches down and it does breach through the wood chips every once in a while.

If we had to blow out 1.5" lines that are 100' long, that would take a ton of air.  Maybe it's possible but I'm imagining it would require a huge compressor.  Or am I overthinking it?

 
Douglas Alpenstock
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An air compressor with a bigger tank (larger air volume) makes it easier, but it's not essential.

Once you have gravity drained the system, the goal is to push most of the water out of the low spots. This can be done in bursts with a smaller compressor, not exceeding the working pressure of the line, and repeated several times.

If working with a smaller compressor, it's really useful to be able to isolate sections and do them one at a time. A half-filled low spot will not burst the pipe; poly is quite forgiving compared to copper.
 
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If its 200ft to the first spigot I would go 2 inch.
Because once all those taps are turned on, at the same time perhaps the pressure drop would be great.
I think the rolls are longer than 200ft, so I would use the rest of it.
If its possible create circles rather than arms, because the water pressure will be more consistent instead of dropping off at the peripherals.
 
Mike Haasl
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Good points John.  It is a community garden where folks will only be watering manually with hoses so I suspect it will be rare to have more than three spigots running at a time.  
 
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I will throw in my 2 cents here.

I have literally run thousands of feet of poly irrigation lines.  As I am hundreds of miles further south than Mike, I only bury the lines 4-6 inches deep, but I agree with the consensus here that I would try to bury the lines at least 24” deep.  I ran virtually all of my lines with 1/2” tubes and they worked fine.  I bumped things up to 3/4” but honestly it made no difference.  I highly recommend drip irrigation as it uses less water yet waters better.

Again, my 2 cents,

Eric
 
Douglas Alpenstock
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John C Daley wrote:If its 200ft to the first spigot I would go 2 inch.


It's true, as a rule bigger is better on the main supply.

Smaller will still work, of course, and you have municipal pressure which is higher than most well systems. It's just that standing around while watering cans slowly fill can be annoying when you've got things to do.
 
Eric Hanson
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Mike, everyone,

Just for reference point, all of my irrigation products come from Dripworks.com.  I found their products to be high quality for very reasonable prices.  I have NOT used drip tape of any type so I can’t comment on those products.  But the tubing products, from 1/2” to 3/4” have worked very well.  Though I thought I was going to get a flow boost by going to 3/4” tubing for the 1st 500’ run, but honestly I just can’t tell a difference.

Regarding the pressure difference coming from a municipal supply—I don’t think you will see a difference as the first part to attach to the water supply is a water filter followed by a pressure regulator to drop water pressure for the poly tubing.  In my case that meant dropping from 80psi to 30psi.  The larger diameter tubing gets more expensive quickly but if that’s what you want to do, go for it!

Just a thought—how are you digging the trench?  I would think the easiest way would be to rent a little walk-behind trencher.  When putting in the water line to my house I rented a 24” deep trencher (as opposed to an 18” trencher).  The 450-500’ long trench took a couple of hours to dig, followed by another 2 hours to clean out the 6” of crumbs that fell back into the trench.  In the end I have a 24” trench which is plenty deep for our frost line.

I can only guess how hard it would have been to dig the whole line by hand and I think a small backhoe would have been overkill.  I think you will be very happy with a trencher.

Best of luck on your project and please keep us updated!

Eric
 
Mike Haasl
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We'd be renting a trencher for sure.  We do have a small backhoe if we run into bigger obstacles but it's generally pretty sandy.

I was hoping 1" would be big enough.  The bigger stuff is even harder to wrestle into a straight line on a 40 degree morning :(

Eric, I have suspicions that with the normal snow cover I have up here, frost doesn't get as deep into the ground as it does down by you.  I think the only reason our frost depth is 4' is for places where the snow has been removed (roads, sidewalks, covered open areas).  But that's just a suspicion.
 
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I'm in the second of three houses on a gravel road and the water company ran 1" to my house and the third house. I don't know about the first house in the line, but I suspect it's one inch to it, too. I never see too much of a water pressure drop.
 
John C Daley
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You can actually do the calculations and determine the pressure drop across any system.
Remember when you have all systems open, in a dry period thats when you may wish to have a bigger supply pipe.
The cost of the pipe is not much compared with the effort to install the wrong sized pipe.

I did not want to pull rank, but I am a Civil Engineer who has dealt with water supplies.

The test is when maximum usage is occurring and I know from experience, standing in a community garden waiting for a bucket to fill is not fun.
Looking at the drawing it appears as if you may have 400ft to the last spigot plus the extra hose length from the water supply point.
you would need more than one roll of pipe, so one could be the big one.
Yes unrolling 2 inch pipe is difficult, but if you roll it alongside a flat bed truck and roll it out, it will be easier.
 
Eric Hanson
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Hi Mike,

I was just running some basic numbers and had a couple of questions for you.  Mostly, how long is your main line and how many gardens will be fed?  The reason I ask is that I was looking at Dripworks.com and they have a great supply of different irritation systems, but the most affordable are definitely designed for a traditional garden hose threaded fitting, probably bottlenecking the ultimate flow rate.

I typically ran a 1/2 inch tube. But switched to a 3/4 inch tube thinking I would have fewer friction losses.  In retrospect I don’t know that it made a difference and I have thousands of feet of tubing buried.

It is possible to go to 1, 1.5, and even 2 inch tubing (and filters, pressure regulators and all other associated equipment), but the price adds up quickly.  My thoughts are that if you don’t have a long run or a lot of garden beds then stick with hose thread and 1/2 inch mainline tubing, but that is just based on my experience.

Whatever you do, good Luck!

Eric
 
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Count me inline with Eric. 1" main should be plenty sufficient. I have worked with poly a lot as well and have also found 1" - 3/4" to work great. Some of the savings could be invested into a sign explaining the water system's limitations and requesting  that folks be conscious of how many spigots are in use to make the flow more efficient. Also consider encouraging gardeners to purchase their own drip line and timers for their plot maybe?
 
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Mike, Another route that you could take, would be to run three 1" lines of poly pipe (home runs to the meter pit, in separate trenches) so that each pathway has it's own feed. This would help with delivering volume, but mainly help by being able to isolate zones of the system for repairs in case of leaks, and for blowing each section out in the fall. Also, pipes in the pathways is better than under any garden plots. NO DIGGING ALLOWED in the pathways, and no digging up someone's garden required for repairs! Install a valve box near the meter and set up zones with tees and PVC ball valves. You could even install a spigot at the meter, so you could have a place to get water if the remainder of the system is OFF, or an easy place to hook up a compressor (near street, to hire an irrigation company for a blow-out with a big compressor), or a siphon hose (if the street is lower elevation)

Spend the extra few bucks for the NSF/potable water poly, somebody is going to drink from this for sure.
The Oetiker pinch clamps are great, a bit easier than gear type hose clamps, and permanent. I agree that with the torch it is easy to cook the pipe, so keep your distance, and move the pipe/torch around, and it doesn't take much. If the pipe starts to look shiny, you are melting it.  

If you are making your spigot risers with metal pipe (especially copper pipe), you need to watch out for hard frosts if the system is still wet. Avoid using metal ball valves for the spigots, I've lost a few due to the fact they trap water either in the ball (off) or around the ball (on, or even partly on) and may crack when frozen. We use the handwheel type with the rubber washer since and haven't had trouble since.

We are lucky at our place to have our meter in a pit at the top of the property ~10' higher than the rest, which then has a 1'/100' slope, and a 50' hose from the farthest spigot reaches the riverbank for another 6' drop... the first few years, I blew the system out, but then did it by gravity to the river, and it's so much easier. You might even consider 300'-400' of hoses linked together, if it could get you to a lower elevation than the system to siphon it out.
 
Mike Haasl
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Thanks for the additional input.  I did get to talk to the city water guy and determined that we have too many hurdles to do the work yet this fall.  So I have a few months to sort out the details.

He did think that 1" for the whole garden would be enough.  Doing home runs sounds like a nifty idea as well.  Then we would be able to keep the lines under the paths...

I hadn't thought about the ball valves freezing even if we winterized.  But the valve on the water heater behind the Wheaton Lab shop froze that way and I agree that it's very likely.  I don't like quarter turn valves but if I can find 1 revolution valves I'll probably go for that.

I think we'll allow people to set up drip irrigation but they won't be able to keep it hooked up all the time.  All the gardeners need access to the spigots so they'd have to run the hose to their system, hook it up, water as they weed and then unhook afterwards.  

Eric, the main line from the street to the meter will probably be 200 feet. Then if we did a home run with 3/4 or 1" lines, the longest one would be 200' and each home run would run 2 or 3 spigots.

Kenneth, that's an excellent point about potable water pipe.  I didn't actually know there was such a thing but I'm gonna go with that for sure.  If people can't drink it, why should we feed it to our plants?  I'll also do my best to get potable water hoses.  And those clamps look pretty cool.  Do you just crimp/clamp them with a pliers or do you need a special tool?

Our site is pretty flat but we might be able to get a siphon going.  I'll have to look at it again.  With 2000 feet of hose I'm sure we could do it, just not sure with a few hundred...
 
Kenneth Elwell
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It is a special crimping plier, looks a bit like a dull end nipper, they’re about $30.00. If you go to an irrigation supply, you’ll probably find the Oetiker brand, but I think it’s the same as the Apollo brand you’ll find at a box store like Home Depot, Lowe’s, Menard’s... you’ll also find larger quantity packs of the rings, and barb fittings...
 
Mike Haasl
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Awesome, thanks!
 
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