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Old 06-04-2011, 03:27 PM   #1
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Sprinklers design

My front lawn is irregular shape. I am plannig to install new sprinklers. I am confused in terms of their head to head to coverage.

When I put 180 degree sprinkler ( 15 feet coverage),
does it cover 15 ft radius including the area near to the sprinkler or not ? If it is yes,

Then I can put another 180 degree sprinker (15 ft coverage) 25 ft apart so that they both together cover half of my area ? This way, there is a overlap of 5 ft at the head level.

1) Does this above idea make sense ?

PSI of incoming water from the source after the backflow value is - 70 PSI. GPM is - 27 GPM. Water meter size - 1 "

Each sprinkler I am going to use is 1.5 GPM. I will be using 3/4 inch SCH 40
line but when it is connected to sprinklers, it is 1/2 inch.

If I connect all the branches, I will be using 100+ ft of pipe to install 10 to 15 sprinkers. (Depends on the above questions answer).

Now the question is - Can I use one 3/4 " valve to connect 10 to 15 sprinklers ? should I have to use 2 valves ?

Please help me.
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Old 06-04-2011, 04:45 PM   #2
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The coverage pattern of one head should cover to the next head, or nearly so, for good coverage. Most of the lawn irrigation manufacturers have lots of into on their web sites. Some even will do the planning for you if you submit a diagram to them, to include the BOM (bill of materials).
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Old 06-04-2011, 11:25 PM   #3
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When designing irrigation systems for a living I learned the triangular spacing method. It might sound complicated but stick with me.

You will need a piece of tracing paper, a straight edge and a 45 degree triangle. It helps me to have a compass too. Decide on a 1/4 inch or better, 1/8 scale to work with and use graph paper if easier.

Start by assuming you are going to use the same output sprinkler heads. Don't worry about what patterns you need yet. Use the manufacturer's LOWEST suggested spray range for the sprinklers and measure out that distance along a straight line across the top of the tracing paper. Now use the triangle to do to the same, with the same dimensions left and right. Work your way down the paper until you have a whole series of of triangular points.

These points are your ideal sprinkler head locations.

Now then, as mentioned, it is easier for me to visualize irrigation design by swinging circles matching the lengths of the triangle sides from each point. What you will see if you do this is a near perfect, no gap, coverage in sprinkler coverage? Amazes me every time.

So let's scale out your yard that needs spray sprinklers. Then lay down and twist and and turn that grid I had you create over the top to locate your sprinkler heads so they water as much lawn as possible but as little is wasted watering sidewalks, driveways and so forth.

Now you can start making decisions on what sprinkler patterns you need, 1/2, 1/4, 3/4, full circle or whatever.

Anyhow, when done. Punch through the holes in your sprinkler grid to your scaled drawing. Figure out the pressure and water load to determine how many circuits you need and you should be good to go. Transfer the sprinkler head locations on the scaled drawing to the yard. Suit me if I screwed this up for you.

Make sense?

Last edited by user1007; 06-04-2011 at 11:29 PM.
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Old 06-04-2011, 11:41 PM   #4
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I'm confused by your post.
27 gpm out of 3/4" is a recipe for water hammer. I'd recommend 1" pipe.
Regarding the head to head, to achieve distribution uniformity, the throw must reach the closest head. Rotors distribute the majority of water at the end of the throw, therefore, closest to the head get a fine mist. That's why the closest head has reach the next rotor.
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Old 06-04-2011, 11:42 PM   #5
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By the way, I think you might have enough flow rate to run all those sprinklers on one line but I would split it in two. It will not cost you that much more. I suspect you do not have the needed PSI demanded by all those heads to keep them all at max performance on one circuit though? What does the manufacturer say the PSI draw at each sprinkler head is by the way?

You can do the math as well as me. If you are starting with 70 psi, you will lose some pressure every inch of pipe running and pipe fitting turn. The risers to the sprinkler heads and the fitting them will steal a bunch and then the heads themselves demand how much? You will maintain some pressure dropping to 1/2 pipe near immediately but then you lose flow rate.

Just do two circuits. 1/2 inch or 3/4 your choice if split in two. 1/2 fittings will save you some chimp change to buy a cooler irrigation timer.
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Old 07-07-2011, 05:00 PM   #6
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Originally Posted by cprao View Post
PSI of incoming water from the source after the backflow value is - 70 PSI. GPM is - 27 GPM. Water meter size - 1 "
Your water pressure sounds abnormally high. Domestic pressure regulators are normally set in the factory for 50 PSI, although 50-60 PSI is an acceptable range. Higher pressures put excess stress on plastic valves in washing machines, dishwashers and irrigation systems and can lead to premature valve failure, including cracking of the valve housing. Before proceeding on your project, you may want to get a known-good pressure test gauge and see if you can adjust the regulator in the 50-60 PSI range. If you can't, the regulator may need to be rebuilt or replaced. (At 70+ PSI, your plumbing may be exposed to the full water main pressure if you're on a city water system. It's 100 PSI at my house, enough to burst garden hoses.)
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