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Pdross

New Member

1

Saturday, September 3rd 2005, 7:43pm

Calculate Sprinkler Capacity

I used the Toro pressure and flow gauge to determine static pressure and flow of my system. I connected this to an outside water spigot. I have a well (with a submersed pump)- that has a 3/4" copper pipe coming from the pressure tank - and then 1/2" pipe going to my outside spigot. When tested, the static pressure was 40psi. I was only able to get 5.5 gpm at 20psi - and 7.5gpm when it was fully opened (and 0 psi). I plan to connect the irrigation system to the 3/4" pipe - and go to 1" poly pipe after the values to the sprinkler heads. Right now I have the heads placed 30' apart - there are 5 zones - each zone runs about 100' - total area about 120' x 90' - flat. 3 questions: Do I have enough water flow for an irrigation system? How much will my gpm increase if run off the 3/4" pipe? Should I connect the irrigation system before or after the pressure tank? Thanks for any help!!

RidgeRun05

Supreme Member

Posts: 314

Location: USA

2

Saturday, September 3rd 2005, 8:04pm

40 PSI is on the very low end of operating an irrigation system. Especially if you take into consideration the friction losses for a backflow device, pipe, valves, and any other component which reduces the water pressure. I am not sure I am understanding your math correctly. You are saying you are flowing 7.5 GPM at 0 PSI? that is not possible. In order to flow a GPM, you must have some type of water pressure.
Tony Posey
Ridge Run Landscapes

Pdross

New Member

3

Sunday, September 4th 2005, 6:16am

When using the Toro flow meter, the "static" pressure dial dropped to zero when I opened the valve (wide open) to measure the GPM. If I closed down the valve a bit I was able to register something on both dials (eg: 20PSI, 5.5GPM). Maybe I am using the meter incorrectly. Is there a way to adjust/increase the pressure from the submersable pump (or the pressure tank in the basement)? Our well is about 100ft deep.

Wet_Boots

Supreme Member

Posts: 4,080

Location: Metro NYC

4

Sunday, September 4th 2005, 7:35am

Better to just read the gpm at the Toro device, and go back to the well tank to read the pressure there. If the pressure switch is set for a 20-40 psi operating range, you could adjust it to raise the shutoff pressure to 50 psi or higher.

Pdross

New Member

5

Sunday, September 4th 2005, 8:56am

I just tried your suggestion. The flow on the Toro meter read a steady 7.5 GPS while and the pressure gauge on the well tank dropped from 55PSI and leveled off at 40PSI. When I turned on a second outside faucet (and kept the first running)the pressure dropped to about 20PSI but I was pumping about another 5 GPS. There is a 1/2" pipe to these outside faucets but I plan to connect my irrigation system to the 3/4" pipe coming from the well pressure tank. Can I safely assume that the pressure will stay pretty much the same while the GPS will increase somewhat? I plan to use the Hunter PGP Arc Rotors - some running at 180 degrees and others at 360 degrees. Can I adjust the ones running at 180 to spray half the amount as those running at 360 (so I have consistent watering across both areas)? If so I can finally figure out how many rotors I can handle in a zone. Thanks again for your help. I think I'm pretty close to understanding this now.

RidgeRun05

Supreme Member

Posts: 314

Location: USA

6

Sunday, September 4th 2005, 11:11am

www.irrigationtutorials.com - This is a great site for getting started planning a proper irrigation system. I think you'll find some useful advice there. As for the same flow rate out of the sprinkler heads, just use the same size nozzle in the head. The radius won't have anything to do with the amount of water output.
Tony Posey
Ridge Run Landscapes

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