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Irrigation Flow Meter Accuracy
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NoAguaFarms
Posted 7/27/2014 14:53 (#3988412)
Subject: Irrigation Flow Meter Accuracy


Texas Panhandle
Center pivot / flow meter question here. In general, are flow meters placed AFTER the booster pump on center pivots very accurate? I installed a new pivot this year, and went ahead and put a flow meter on it, as this was a new farm, and wasn't quite sure of the total water volume, or how much it would fluctuate during the season. Here is my scenario:

1/4 mile pivot nozzled @ 800gpm Pivot operating pressure per the Senninger chart is 25lbs at pivot 15lbs at first IWOB and 5lbs at end nozzle (30 inch drop spacing) . Open flowing the wells into the pivot (no booster pump), flow meter shows 900 gpm at start of season, 750 now in the heat of summer, but never more than 13psi at the pivot. 35-40 lbs line pressure, nozzle pressure at first nozzle in line with chart, a little light at the end nozzle.

With the booster pump on, pivot now shows to be at operating pressure (25 psi), but shows 25 lbs at first nozzle and 15lbs at end nozzle. Flowmeter showing a range of 1050-1100 gpm. Line pressure pulled down to 10-15psi

My question is, which is going to be more accurate, the flow coming through the flowmeter, or the pivot operating pressure? Hard to believe the pressures on the chart from Senninger would be off so much, the other pivots operate accurately at published pressure, so I'm wondering if having the flowmeter installed on the upright pipe just above the booster pump is throwing off the reading, and it may be more accurate if installed on the horizontal pipe after the elbow. Getting into the dog days, so any wells we can rotate out would be helpful...hoping the flowmeter is right and pivot pressure is just wrong.
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