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New Member


Friday, March 5th 2004, 4:34pm

2 acre design question

I have a 2 1/4 acre yard in a ranch setting in Texas. I want to irrigate it and keep the cost's down. I had a large irrigation supply firm here design me a system. They did and it basically consists of 16 zones. The yard is all done with Hunter PGP's with #5 nozzles, 30' radius - 8 rotors per zone. The beds are hunter srs. My question is this...They have "textbook" soild head to head {every 30'} coverage on all 2 acres of grass. I see that I can cut 5 zones out by spacing the rotors out a little more, while there are no "dry" spots there are some area's that are not ovelaped. How critical is it to have "head to head coverage" as this is acerage and not a golf course. I think this forum is great info and I appreciate any feedback anyone can give.


Supreme Member


Friday, March 5th 2004, 6:06pm

The reason for head-to-head coverage is because the amount of water reaching the ground varies based on distance from the head.

While this is not a quote of any specific system, here's a represenative example.

Place several rain guage in a row spaced 1 foot apart starting 1' from a lone sprinkler head (i.e. pretent that all other heads have not been installed yet). Let the system run for an hour and come back and check the water level in each guage. The first one has 2" of water. The second has 1.75". The third one has 1.6". etc, etc until the last one has 0.5". So if you install another head at the last rain guage (and turn off the original head) turn the water on again and you get the same results (execpt backwards, the last one that is now closest to the head is the one with 2"). So now if you try it a third time with both heads on, the first and the last guage will show 2.5". All the others in between will also be close to 2.5" (with perhaps as little as 10% difference, where as with one head, the level varied by 300%).

Keep in mind this is a totally made up example (for all I know, its the gauge farthest from the head that got 2" and the closest got only 0.5). But it still shows how by having all points between the heads getting water from both heads, the 2nd head makes up for the short commings of the first.

I think I've read the general suggestion is that if you don't want 100% overlap like the designers did it, it's a general rule of thumb that you're ok as long as you have at least 80% overlap. That means if the system was designed with 100% overlap on 40 foot head spacing, you should not increase the head beyond another 10 feet (i.e. 50 foot head spacing).


New Member


Saturday, March 6th 2004, 4:50am

Thanks for the response! One reason that I question the head to head coverage is that our septic system has 3 spray heads. Each sprays a 30' radius, they are spaced 60' apart. While I realize that this spacing is too extreme for a sprinkler system, the grass looks great in that areas with no evident "dry spots" or visual evidence of varying water coverage. I do realize that septic water has "nutients although we have a "chlorinator" so the water is pretty "clear". Again if I had a "normal sized yard" I wouldn't question the proper coverage but I am getting into some considerable cost'a coveribg this 2 1/4 acres with "head to head" coverage.

rain man

Active Member


Monday, March 8th 2004, 3:52pm

Hunter PGP's have a through radius up to 50' at 60psi. However, designers typically won't space more than 30' due to wind affecting your overlap. I designed my own system w/ PGP's at 43' spacing and coverage is fine. Just make sure you have the pressure to get the coverage where it needs to go.


Advanced Member

Posts: 229

Location: USA


Monday, March 8th 2004, 5:03pm

I would not touch a thing on that head to head coverage. That is the way to design.

What is your water source? Well or Town Water. A well would be the way to go for more cost effectiveness.


New Member


Tuesday, March 16th 2004, 3:11am

Thanks for the good advice. I placed 9 zones around the house extending out into most of the yard with PGP head to head coverage at 30' R and 2 zones overlaping coverage...

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