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Design Help??

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Sticks_gms

Active Member

Posts: 8

Location: USA

1

Thursday, February 26th 2004, 2:37am

Design Help??

I am getting ready to install a new sprinkler system on a 1.5 acre land. I have plans from rainbird who did the design and I have some questions about design and pipe size? here is what I have: 1 1/2 pump(well) with 1 1/4 feed from the pump to the house with a split inside the house one for house water and one for sprinkler. I will be running 2 lines of copper of 1 1/4" to the north side of the house and to the south side of the house (inside) I will be installing 2 backflow valves (1 1/4") at each location from there I will switch to PVC to the manifolded valves for eac zone! the reason why is because I have a walkout backyard and the BF valves will start as the grade/slope changes! my first question is Rainbird called out to run 1 1/4" from the valves to all of the sprinkler heads. so from the valve to each sprinkler head is 1 1/4" (funny pipe) or (PVC) they said it didn't matter which?? so here lies my question what size pipe do I use? because the valves are 1". so Rainbird is saying run 1 1/4" to the valve reduce to fit the 1" valve and then go back to 1 1/4" to the sprinkler heads in that zone of which I will have a total of 12 zones for sprinklers consisting of 6-9 sprinkler each zone. and 2-3 zones for drip heads for the flowers! my second question is is it right to the zones in a straight line for instance from the valve a straight line from the first sprinkler head to the last?? thank you for your time and your responses just as an FYI my pump will run
30 - 36gpm!
Kevin

HooKooDooKu

Supreme Member

Posts: 683

2

Thursday, February 26th 2004, 3:46am

There is nothing wrong with using a smaller valve with a larger pipe.

The primary purpose for larger pipe is to reduce pressure losses over a long run. The larger pipe also allows for a lower velocity for a given gpm (higher velocity can lead to water hammer).

Example: With Sch40 PVC at 30gpm: 1" pipe has about 18psi loss over a 100' run (and the water flows at 11ft/sec TOO HIGH!!!!). 1-1/4" pipe has about 5psi loss over a 100' run (and the water flows at 6-1/2ft/sec, still high, but not too high). 1-1/2" pipe has about 2psi loss over a 100' run (and the water flows at 5ft/sec, a safe speed).

If there is going to be 30gpm flowing through your sprinkler system, I'd say that a 1-1/4" pipe is too small and you should use 1-1/2" (with the 1" valve still being fine). Based on the pipe charts I'm looking at for PVC, I wouldn't use 1-1/4" UNLESS the expected flow is 25gpm or less.

As for sprinkler heads being in a strait line, again, pressure losses are what is important. You want all the heads to be operating at about the same pressure (you don't want 30psi pushing on the 1st head with only 15psi on the last). From what I've heard, a pressure difference of about 5psi should be ok, and with 1-1/4" pipe, that means at a flow rate of 30gpm, the first to last head in a strait line can be upto around 100' apart.

Sticks_gms

Active Member

Posts: 8

Location: USA

3

Friday, February 27th 2004, 2:17am

Thank you for the response!! excellent!! from what I can see most of the runs are going to be 5 to 6 heads at a 30' to 33' spacing so that gives me a run from the first head to the last about 180' and with a 30' to 50' run from the valve to the first head. will this create problems as far as lining up the heads in a straight line and preasure loss?? because all of my long runs are in the backyard where I have about 200' from the house to the property line the front has about 60' to the street so that will not be an issue it's the back that I am worried about?? Thank you again for your input!!
Kevin

HooKooDooKu

Supreme Member

Posts: 683

4

Friday, February 27th 2004, 3:55am

You have not quoted what your gpm is going to be for the heads that will be installed. So again, assuming about 30gpm and 6 heads, that's 5gpm per head (and assuming 1-1/4" pipe for all of it).

For 1-1/4" Sch40 PVC, Here's the approx loss tables:
5gpm = 0.2psi/100ft
10gpm = 0.63psi/100'
15pgm = 1.7psi/100'
20gpm = 2.7psi/100'
25gpm = 3.0psi/100'
30gpm = 4.8psi/100'

House to 1st head = 30gpm
1st head to 2nd head = 25gpm
2 -> 3 = 20gpm, 3 -> 4 = 15gpm, 4-> 5 = 10gpm, 5 -> 6 = 5gpm
So you can figure the pressure loss in each section with the data above and calculate the expected pressure difference (assuming you're on a level slope).

If your flow rate is really this high, I would consider using 1-1/2" Pipe all the way to the 2nd head. Then use 1-1/4" from there to the rest of the heads. If you want to keep up with a bunch of different pipe sizes, you can even continue to use smaller and smaller pipe as you get to the end of the run (such that the last head is feed by a 3/4" pipe"

To calculate what your pipe needs really are, you have to know what the gpm per head is really going to be. At least one place I've found pressure loss tables was at www.hunterindustries.com

Sticks_gms

Active Member

Posts: 8

Location: USA

5

Friday, February 27th 2004, 5:43am

Thank you!! I am sorry yes the heads will be using 5gpm nozzles. a different question I am thinking of using blazzing saddles instead of barb fittings pros and cons?? I plan on using funny pipe? 1 1/4" Thank you
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