This tool also helps evaluate management practices, determine pump efficiency
and detect well pump and irrigation system problems.
By Chris Henry
Water Management Engineer
University of Arkansas, Division of Agriculture
How many of us would buy gas from a service station that did not report how many gallons of gas we purchased when we filled up our automobile? Probably not many. So why don’t we measure our water use when we irrigate?
A flow meter is a valuable tool for improving irrigation efficiency, evaluating current management practices, determining pump efficiency and detecting well pump and irrigation system problems. Flow meters are a useful tool to help understand water use and pump performance in agriculture.
First, knowing how much water is being used for irrigation is needed to make informed decisions about changing crop management. Having historical knowledge about water use allows growers to understand how weather patterns impact irrigation needs and how different management choices impact water use on their fields.
An example of a water management change would be the application of a surge valve. Comparing water use from one year using a surge valve against historical water use can help evaluate the effectiveness of this change on the water savings and the potential payback on such an investment.
Optimize pumping in season
Probably the most compelling reason to have a flow meter on a pumping plant is to optimize pumping during the growing season. Wells draw down during the season, which means that pumps produce less volume (because of a higher total dynamic head) as the growing season progresses. For engine-driven pumps, the engine speed can be adjusted to provide the most water with the least amount of fuel, often referred to as the “sweet spot.”
By tracking fuel use and water flow, a grower can determine the engine speed that provides the most water with the least amount of fuel. Simply throttling an engine down a couple of hundred RPMs with only a modest reduction in flow can provide substantial fuel savings.
Saving 0.2 gallons per hour on an irrigation pump that used 1,000 hours per year just about pays for a new flow meter. Flow meters cost about $1,000 and are easily installed in most situations. Turbine style flow meters are the most popular and cost effective, although there are many different models available. There are several electronic style flow meters, which have few or no moving parts and are a better solution for surface water sources where there is a concern with turbine plugging.
Much like an RPM gage on an engine, a flow meter acts as a diagnostic tool for the pump. Over time, pump capacity declines. A flow meter is a useful diagnostic tool for predicting pump repair before major servicing is needed. Pump capacity sometimes changes abruptly, which may be an indication of catastrophic failure. Often, if pumps are serviced when this occurs, repairs are considerably less costly. Responding to this indicator can save thousands of dollars on repair bills and downtime, paying for the flow meter several times over.
Ideally, flow meters should be installed with no obstructions five pipe diameters in front of the turbine. Flow meters with acreinch totalizers, as opposed to traditional gallons, make the math easy in calculating water use. Simply divide the volume of water used by the acres irrigated to determine the inches of water used.
For those who have flow meters, watch for condensation on the dial face as this is an indication that the meter needs to be serviced before any additional damage occurs. Meter lids sometimes break and should be replaced to keep out sunlight, otherwise the meters operate at higher temperatures that decrease meter life. Turbine flow meters are calibrated at the factory and can last 20 to 30 years or longer if properly maintained.
In summary, flow meters are useful tools for recording water use, as an indicator for the impact of management changes and a diagnostic tool for pumps that can help growers improve their bottom line.
Contact Henry at (870) 673-2661or via email at CGHenry@uark.edu.