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HooKooDooKu

Supreme Member

11

Monday, May 9th 2011, 9:18am

My meter reads 0-1-2-3-4-5-6-7-8-9-0 and as it goes from 0 back to 0 it only takes 6.4 seconds...unless the new meter is reading wrong or I'm somehow calculating wrong it's 98gpm.


If I'm reading this correctly, you are claiming that your meter records 10 gallons in 6.4 seconds. Well that equates to 93.75 gpm, not 98.

But I agree with the others that your numbers sound way too far out... as if you were off by one decimal point, that what you think is 10 gallons in 6.4 seconds is more like 1.0 gallons in 6.4 seconds.

If your meter is actually capable to producing something on the order of 100gpm, then the pipes would have to be 1-1/2" PVC just for the flow rate to show on any flow tables, and at that, the flow rate would be more than 15fps, and speed three times beyond what building codes allow, and would be incurring pressure losses of 20psi for every 100' of 1-1/2" pipe. To properly handle a 100gpm flow would require 3" PVC pipes.

By contrast, 1 gallon in 6.4 seconds equating to 9.375 gpm sounds a lot more like an appropriate flow to expect from a 1" meter than 93.75gpm.

12

Monday, May 9th 2011, 12:47pm

Mitchgo, I'll send a picture as soon as I get home. I like the idea of running a 2" main line, and only 8 sprinklers.

I don't want to put sprinklers on the field because of the extra work and dangers with malfunctioning sprinkler heads. I realize it's probablly not a realistic issue, but if I can avoid doing so I would like to.

Your idea for 8 sprinklers would be if all were on the playing surface right. If so I might do it just because of the small amount of sprinkler heads needed. I was told by someone else that in order to get head to head I would need 28 sprinklers on the field (perhaps the sprinkler heads were much less effective). That was before I knew I was going to have so much gpm.

Thanks,

Jason

13

Monday, May 9th 2011, 4:30pm

Pick of meter.



I agree the numbers sound way off, bit if so I'm just figuring something wrong like the 93/98 gpm you pointed out. I'm sure I get more than 9.3 gpm though right ;(
jason9520 has attached the following file:
  • meter.jpg (8.96 kB - 6 times downloaded - Last download: May 10th 2011, 5:06pm)

14

Monday, May 9th 2011, 8:08pm

In order to verify the meter and readings I used a 6gal. bucket (6gal on bottom of bucket). Turned off everything in the house and opened up a faucet from the house. The meter read 6gallons used and the bucket was all but about 1.5" from the top. Thus I'm willing to say that the meter is reading gallons and that's 4.6 seconds and 6.4 seconds for 10 gallons on the two attempts at measuring at the T valve next to the meter.

FYI the 25' hose at the end of a faucet from the houses exterior ran the 6gallons in 32.6 seconds thus approx. 11 gallons a minute.

Jason

15

Monday, May 9th 2011, 11:28pm

Meter is a model 70 badger 1" meter.

I tried to calculate the 2" pipe from the meter to the field and then the 1.5" pipe to 4 zones and couldn't figure out what the calculations meant. The "engineers toolkit" website spit out negative numbers even though I was considering only one zone at a time. My understanding of the gpm and psi losses are non-exsistent. I'm sure also that my zoning and sprinkler placement could be better. I think I would need approx. 50-65' of throw from these rotors in order to reach one to the other (head to head). Using the Rainbird 8005 this would be 65' with 21gpm and 50 psi. or 19gpm at 80psi. In order to run two sprinklers at a time I would need approx. 40gpm and between 50-80psi?

Do I also need double the psi, or am I wrong about all of the numbers?

Here is a scetch of my current idea of piping which includes sprinklers on the field. Please let me know how I can improve the design. I want this done right and only once as I will be doing the work myself to order to save $. I want it to seem as though I knew what I was doing you know.

Thanks again,

Jason
jason9520 has attached the following file:
  • zones.jpg (18.98 kB - 4 times downloaded - Last download: May 14th 2011, 8:38pm)

Wet_Boots

Supreme Member

Posts: 4,027

Location: Metro NYC

16

Tuesday, May 10th 2011, 1:19pm

You have to know that sprinklers do not effectively throw further, in feet of radius, than their input pressure, in psi. Simply put, you will not be getting even 50-foot throws from a one-inch meter and a static pressure of 85 psi.

HooKooDooKu

Supreme Member

17

Tuesday, May 10th 2011, 5:33pm

It's a lot of reading, but if you want to begin to get an understanding of what needs to be done, then you need to read over the web site www.irrigationtutorial.com

But to get started with a few calculations, check out the charts here (specifically the page for Sch40 PVC: http://www.hunterindustries.com/resources/pdfs/technical/domestic/lit091w.pdf

One design rule is that water shouldn't travel faster than about 5fps. Based on the chart, you can see that at 10gpm, your water will flow at 6.0 fps in a 3/4" pipe, and 3.7fps in a 1" pipe. So 1" is your minimum size.

The next rule of sizing pipe is that water flowwing through a pipe loses usable water pressure. The chart will further show you that at 10gpm, you will loose 2.4psi for every 100' of pipe. Since you are talking about hundreds of feet, your pressure losses could quickly grow to about 10+ psi. Given that you are starting with 85psi, you've got some room to work with (however, other things will "steal" pressure from you as well). The chart will also show you how small increases in pipe size GREATLY reduce the pressure losses. This is because the pressure loss is a function of the square of the water speed, and water speed is a function of the square of the pipe size. So doubling pipe size cuts pressure losses by a factor of 8. So once you have a clue about all your pressure losses, you can price various pipe sizes and decide which size gives you the most bang for the buck. You're likely to find that you don't really need a 2" line, that 1-1/2" or 1-1/4 will do fine.

The next rule to consider in designing the irrigation system is how far the heads can throw water. The basic rule of thumb that Wet_Boots was giving you is that what ever is the left-over water pressure at the head in psi (after all the losses are considered from the meter, a backflow preventer, valves, and pipe) you can not expect the water to throw farther than that in feet. So if you wind up with only 30psi at the heads, you can't expect a throw with rotors of more than 30 feet. With the pipe sizes and flow you are talking about, 30psi at the heads should be very easy. Likely, once all is said and done, 40psi (and therefore 40') are reasonable expectation. But 50' of throw requires high end rotors AND a minimum of 50psi. That only gives you 15psi to lose through all the equipment listed above. That might or might not be possible. For example, if local building codes require an RPZ backflow preventer, you can expect the RPZ to steal 12-15psi all by itself.

Now practically speaking, my only irrigation experience has been designing and installing an irrigaition system myself for my home. But my best guess at this point is that you need to start by designing for 40psi at the spray heads (which means a maximum throw of 40' with rotors) and work backwards from there.

Wet_Boots

Supreme Member

Posts: 4,027

Location: Metro NYC

18

Tuesday, May 10th 2011, 6:16pm

Better to ring the field boundary with sprinkler heads, then fill in the middle of the field. The cost of water being what it is, you do better to apply it more precisely.

Mitchgo

Supreme Member

Posts: 502

Location: Seattle

19

Wednesday, May 11th 2011, 12:51am

You can get 2 8000's shooting 50' each at 50 psi with a 1" meter at 85 psi static

20

Saturday, May 14th 2011, 11:55pm

Great tutorial!

I checked the psi from two places off the house and both read 103psi. After figuring the losses from the backflow preventer, mainlines, valves, and 50psi for sprinklers I totaled 75psi loss.

I'm a little disappointed that the max gpm I should be taking from my 1"copper line is 18gpm.

I'm also concerned with using only 8 rainbird 8000's. I can't figure how I can get head to head coverage.

The tutorial calculated that I should run a 1.5" mainline giving me 2.8ft/sec when using 18gpm. I suppose what will keep me at 18gpm is what I choose to run off the line. In other words if I set up 4 zones running two sprinklers a zone and deciede to open two zones at a time then I could increase the gpm used but I'd be placing a strain on the pipe?

Thanks for yall's help

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