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JeffM

New Member

1

Saturday, April 16th 2011, 10:09pm

Design for Rainbird 5000 series

Hi, all. I have 12 gpm at 60 psi through 3/4" pipe.

I want to irrigate almost 2 acres. I'd like to reasonably maximize spacing between heads while assuring full coverage. Due to amount of pipe I have to run, I'd also like to maximize number of heads in a zone. What spacing can I use between heads for what size zones?

No misters or sprayers will be used. Just rotors. Also, should I use a 1" trunk to supply a zone, or can I use 3/4" throughout?

Thanks.

Mitchgo

Supreme Member

Posts: 502

Location: Seattle

2

Sunday, April 17th 2011, 12:57am

Is this off your city water or a well/lake?

JeffM

New Member

3

Sunday, April 17th 2011, 1:10am

City

JeffM

New Member

4

Sunday, April 17th 2011, 1:16am

On a side question as well, let's say I get 3.47 gpm for each head.

If, for example, I set one of the heads to cover a half-circle, while others in same zone cover full circle, will the flow rate of the half-circle be reduced to half, or will it deliver twice the water in the same amount of time to the area it targets?

Edit: Just saw that you can switch to a different plastic nozzle to achieve different flow rates. So, I think I have this part answered.

This post has been edited 1 times, last edit by "JeffM" (Apr 17th 2011, 1:24am)


Mitchgo

Supreme Member

Posts: 502

Location: Seattle

5

Sunday, April 17th 2011, 9:56am

2 acres is huge for someone who doesn't really know what they are doing... I like your optimism though

Honestly I think you should get a company in to design the system for you.. Since there not making any money on the install it would probably cost $200-300 but worth it... It would be a shame for you to go spend $2500+ in parts alone and design the whole thing entirely wrong

How did you get that flow rate? A hose bib off the side of the house?

I would consider tapping into your meter and getting a proper flow rate there, using a minimum 1 1/4 Main line to reduce psi loss , using low precip nozzles to maximize the length of the zone ( this means longer run time), and possibly a booster pump .

This post has been edited 1 times, last edit by "Mitchgo" (Apr 17th 2011, 10:01am)


Wet_Boots

Supreme Member

Posts: 4,080

Location: Metro NYC

6

Sunday, April 17th 2011, 9:57am

For two acres, it happens that 12 gpm can be spreading it very thin. You would want to use larger pipe diameter for any mainline or lateral that has to run over 100 feet

JeffM

New Member

7

Sunday, April 17th 2011, 10:28am

Thanks. Yes, it happens I've been reading a manual, and you're right. This is not a design task for the feint of heart.

That said, my heart is not feint. ;-)

Okay, I got the 12 gpm by filling a bucket at a hose bib.

The city's water meter is a 1". I have seen, but will need to verify, that the city maintains 60 psi to the meter.

I am now seeing that, supposing I understand this correctly, I will have to use 1" trunks which will supply 3/4" laterals with no more than 2 of the Rainbird 5000's on each 3/4" line. It looks also like max spacing, assuming a 40' throw, will be 48', which allows throw overlap for the last 40% of throw distance.

The RB 5000 is showing that at 55 psi, with nozzle 3, I will get a 40' throw with a flow of 3.47 gpm. Since my whole supply is 12 gpm, it seems 2 heads is the max I'd want to run at a time, right? (I assume I don't want to use my max available, or a clothes washer or dishwasher or shower will be starved).

I also saw, where if I set up these heads in a square pattern, I will have some drier spots - even if the heads were laid at head-to-head distance. It was suggested the triangular pattern will allow for greater spacing, and the math was shown to prove this, which I completely understand.

So, the dimensions of the back yard approximate 150 x 240, and the front yard dimensions are about the same. My calculations tell me that I will have, for the back yard, 5 heads wide by 3 heads deep, for a total of 15 heads to serve the back yard. Same for the front.

Now, if I'm getting only 2 RB 5000's per zone (max), that leaves me 15 zones. That's a lot of zones!

Do you guys agree with my math?

JeffM

New Member

8

Sunday, April 17th 2011, 11:17am

I already found one error in my assumptions. If I am going to tie into a 1" line, I can't use the 12 gpm reading from the 3/4" bib I used.

At this point, it is just little things like this (which really are not little) that I need to be careful with.

But I did see a chart that says for Sched 40 PVC, to maintain a velocity of under 5 ft/sec, I need to not send more than 12 gpm through a 1" pipe. The same chart says do not send more than 8 gpm through 3/4". So, it still tends to tell me I get no more than 2 RB 5000's per zone.

Wet_Boots

Supreme Member

Posts: 4,080

Location: Metro NYC

9

Sunday, April 17th 2011, 4:01pm

If you are intent on doing this yourself, make your tie-in and install your backflow preventer. Then get a pressure gauge, and start in making pressure-and-flow measurements. Create a chart of flows at various supply pressures. Only then do you go about designing a system.

JeffM

New Member

10

Sunday, April 17th 2011, 5:31pm

I started out thinking that I could do this with about 12 sprinklers, but according to the research I did, it looks like it will require more than 30.

The number of heads, in terms of cost, was not much of an impediment to me, but what is an impediment is that when I do the math and figure if I run each of 15 zones a mere 10 minutes a day, that's 2.5 hours of water. And 10 minutes is hardly anything. 30 minutes each would leave me running water at 7.5 hours a day.

I see a huge water bill if I was to design a system for as much ground as this and actually put the system to its intended use. On this basis, it look like irrigating 2 acres is either (a) for rich people, or (b) nature.

I don't think I am so inclined anymore - that is, unless I am totally missing something here.

Thanks.

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