Pipe size for underground system?

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bountyhunter

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I am getting ready to put in an underground irrigation system myself and have a question on what size of pipe to use. I have thousands of feet of 1-1/4" pvc already, and would obviously like to make use of it. My sprinklers are Weathermatic T3 rotors. They have 3/4 female IPT connections on the bottom of the sprinkler. Can I use the 1-1/4" all the way to the sprinklers and then reduce right before I tie into the heads, or should I run the 1-1/4" as the mainlines and branch off of them with 3/4" poly to the heads(about 10-20' on each branch). Flow at 30psi is 9.5-10 gpm at my house. Thanks in advance.
 
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Alectrician

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1 1/4" plumbing PVC????

Hmmm...

I would use all the "1 1/4" you want to.

30 PSI is not a lot of pressure though. Install a couple of heads and test before you install the whole thing.
 

bountyhunter

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My static pressure is 40psi, but when I open the flow valve down to operating pressure(30-35psi) I get my flow of 9.5 gpm. I will try a few heads and see what happens. You think the 1-1/4" pvc will be good all the way to the heads then? Oh ya, my main line in is 1 1/4" as well, if that matters.
 
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Wet_Boots

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40 psi static puts you into booster-pump territory. (the size of which depends on the size and length of the home's supply line - sometimes, the optimum booster might be as small as a 1/3 horsepower jet pump)
 

bountyhunter

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Enlighten me some on these booster pumps if you will. My main service line into my property is 2" poly pipe and it runs about 2000' from the meter to my house location. From there I go to 1-1/4" pvc to the house and all the hydrants around the property. I tied into the line feeding one of the hydrants for my sprinkler system. Can I put my booster pump there in the 1-1/4" line?
 

Bob NH

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Decide how many GPM you want for the irrigation and get a pump with fairly flat head/flow curve that will give you enough boost to get that much water from the utility.

The pump should be connected so it boosts all of the water you use. It could be linked to the irrigation controller so you will get your existing pressure when the irrigaition system is not running.

Ten psi pressure drop at 10 GPM isn't consistent with 2000 ft of 2" pipe. You should get 20 GPM with only about 8 psi pressure loss.
 

Wet_Boots

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He might have thick-wall CTS poly for the service line, and be flowing more like 1-1/2 copper. The size of the property figures into this. If that 10 gpm is enough for watering all of the lawn, you could use a 1/2 horsepower jet pump, which has a maximum flow of around 15 gpm, which is small enough to not be able to overpump the supply. You still have to have a backflow preventer in the supply line to the sprinklers, and your local codes may require it to be an RPZ device, since your sprinklers will have a higher pressure than the house.
 

bountyhunter

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The 2" coming to the property is 2" Poly, once it gets to my property, I converted it to 2" Sch. 40 pvc. Feeding all the hydrants around the house is 1-1/4" sch 40 pvc. One of these hyrdants is where I did my pressure/flow test. I have now tapped into the 1 1/4" line and have a main irrigation shutoff valve at that connection. I just stubbed a 1 1/4" main sprinkler line above ground for now until I get my manifolds, sprinklers, etc. My plan is to use the 1 1/4" sch. 40 pvc I already have for the entire system. I will just reduce to the 3/4" mpt at the sprinkler heads.

Can these jet pumps be placed in an underground valve box and left out all year? Of course during the winter I will drain the entire system. I am having trouble finding what kind of pump I need online. Can someone post a link to a pump like I will most likely need? Once I see what kind I need, I can search it out better.
 

JohnnyGreen

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Bounty,
Use the number 2 nozzle on the sprinkler. You can use the 1 1/4" pipe but dont use the poly pipe. You will loose alot of PSI. Run 3/4 pvc pipe from the 1 1/4" pipe. from the numbers you gave, 30 psi with 1 1/4 pipe you can get about 20 gpm. At that current rate you will have about 21 psi. I dont understand how you could have 30 psi but have only 10 gallons a min with 1 1/4. Are you shure its correct? Hunter makes the best sprinklers out there and they have a free irrigation system design calculator. Go there and down load it and it will help you alot.
Good luck
 

bountyhunter

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I tested it with this flow/pressure gauge I bought from Home Depot. You are right, 9 gmp does not seem very high for 1 1/4" pipe. I plan to install one zone above ground to test the system out first to see how it will work before getting too carried away with the project. I only plan to install 5-6 heads on a zone, so hopefully this will work out. I am kind of concerned though. These heads are the exact ones the local school uses on the baseball field and they run 10-12 on each zone, but they are quite a bit lower than I am at my house, with the same size pipe feeding both systems.
 

Bob NH

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. . . I will just reduce to the 3/4" mpt at the sprinkler heads.

Can these jet pumps be placed in an underground valve box and left out all year? Of course during the winter I will drain the entire system. I am having trouble finding what kind of pump I need online. Can someone post a link to a pump like I will most likely need? Once I see what kind I need, I can search it out better.

I would use Shedule 80 PVC nipples instead of the "break to length" type often sold by irrigation places. I have seen a lot of those break easily. I have bought PVC nipples or various lengths from Grainger.

The problem with putting a pump in an underground box is that the motors don't always do well in high-humidity "condensing" environments. That is especially the case if you leave it over the winter.

You can't get a good recommendation for a booster pump without knowing the flow that you want, and the pressure at the end of the 2" line when you are using that flow.

A small jet pump as recommended by Wet_Boots is great for the 10 GPM +/- range.

Larger flows in the 20 GPM range could be served by a centrifugal pump such as the Goulds Irri-Gator, or a variation from another manufacturer.
 

bountyhunter

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I have been searching for pumps and about all I seem to come up with are pumps for pulling water from a pond or well for sprinklers. I assume these are not the pumps I am looking for. I will check out the Goulds Irri-Gator, thanks for that tip Bob.
 

Alectrician

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Skip the pump and use more valves/sections.

Skip the math and install a few heads to see how it works.
 

Wet_Boots

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I have been searching for pumps and about all I seem to come up with are pumps for pulling water from a pond or well for sprinklers. I assume these are not the pumps I am looking for. I will check out the Goulds Irri-Gator, thanks for that tip Bob.
Nothing prevents you from using a shallow-well jet pump as a booster. One such pump is a Goulds J5S
http://www.goulds.com/pdf/7297.pdf
 

bountyhunter

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Well I just finished all connections last night and fired it up. I ended up using the 1-1/4" all the way to the head and found some 1-1/4" x 3/4" 90's to go into the heads. I used 6 rotors on each zone and they all cover from head to head as they are supposed to. I am tired of gluing fittings and joints of pipe together though!! Just a little under 2000' of 1-1/4" pipe to do the entire system.
 

Alectrician

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I installed irrigation systems in the early 70's before going into the electrical trade.

I never get a thrill out of turning on lights or energizing equipment but I ALWAYS love to see those heads pop up and spray. I was always partial to the old school impact heads because of the simple mechanics involved.

Good job!

Be patient and set those heads to the proper height !!
 
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