Water Well Journal
Issue link: https://read.dmtmag.com/i/629532
Technical Training First, internally as a manufacturer, it is our responsibility to train the next generation of application and product engineers in the mechanical and hydraulic fundamentals of centrifugal pumps. You may say this has always been the case, and you would be correct. Nonetheless, a tendency within the industry is to streamline training to simply the keystrokes of our application software and electronic systems. In an environment of limited human resources, the pressure to bring new engineering hires online more quickly is obvious. Capitalizing on the efficiency these electronic tools bring is important, but by no means comprehensive. What is needed is investing the necessary time to teach the methodology of pump applications and problem solving. This includes time spent in the various manufacturing processes as well as time spent in the field with customers, during installation, and field service situations. Also required is the patience to overcome the reluctance of new technical graduates coming out of school to manually "go the long way around" and fully understand the logic behind the keystrokes. It is striking to me how differently this next generation is conditioned in learning by growing up with computers. We need to recognize and be sensitive to this. A Sophisticated Market Second, the agricultural pump market is more sophisticated today than what it was years ago. Energy costs and rebates on pumping plant efficiency improvements dictate maximizing efficiency is a priority now more than ever. Variable speed operation is becoming more common as variable frequency drive technology gets more cost competi- tive. It is not uncommon for multiple pumps to be used to sup- port a single irrigation system or a single pump to support multiple systems. The systems themselves are also more complex with multi- ple operating points resulting from corner systems on center pivots and variable rate irrigation (VRI) sprinkler packages. These additional considerations influence pump selections based on the characteristics of the manufacturer's published head-capacity curve and the point or points at which they intersect the irrigation system head curve. Regardless of the seeming complexity of some systems, the interaction of the pump curve to the system head curve is relatively easy to understand and highly predictable when the system head is broken down into its components. Some installation contractors have been successfully ap- plying pumps for years without completely recognizing the in- teraction of the system head components for which they are accounting. This lack of understanding will make applications more confusing as they get exposed to more complex situa- tions as described above. The starting point is generally selecting the pump model by choosing a performance curve (head-capacity curve) to opti- mize the efficiency at the desired system operating point or points. Following the performance curve selection, an accu- rate calculation of the system head curve is essential to make sure you arrive at the desired operating point (flow) on the head-capacity curve. The system head curve calculation is comprised of three components: • Static head: The total lift from the surface of the water (pumping water level) to the delivery point/elevation of the irrigation system • Pressure head: The system design pressure require- ment in feet (psi × 2.31) • Friction head: The head losses in piping and appurte- nances at any given flow rate in the system. The sum of these three components make up the total sys- tem head requirement. Note: These are the head components that are external to the pump. Internal head losses must be added to the final pump design. If the pump has been selected correctly, the intersection of the pump performance curve (head-capacity curve) will occur with the system head curve at the desired flow rate. It merits stating again: It is the intersection of the head-capacity curve with the system head curve that determines the flow rate. An- other way to think about this is to question what does a pump see: head or flow? The answer is pumps see head. This is true at any point within the piping system. Therefore, when multiple pumps are joined in a distribu- tion system or when multiple systems are supplied by a single pump, the performance of each pump can be accurately pre- dicted by correctly evaluating the system head at the point at which the pump connects to the system. Final Thoughts While the technical issues and responsibilities discussed apply primarily to suppliers and application technicians, the business fundamentals described here are more general in nature. They are principles that provide opportunities for organizations regardless of size and across the spectrum of responsibilities to set themselves apart. By investing in the next generation of industry profession- als, they will be increasing their value proposition to their business partners in an ever more competitive environment. In my next column, I want to expand on the discussion I began on matching the head-capacity curve to the system head curve, specifically by looking at curve shapes (steepness vs. flatness) and how that can impact pump selection. WWJ Mike Allen has worked extensively on water issues in Nebraska and was appointed by the governor to the Water Well Standards and Contractors Licensing Board in 1999 and served as chairman until 2013. He also served two terms as a director on the Little Blue Natural Resources District Board of Directors and serves on the Board of Directors of the Nebraska Water Resources Association. Allen currently serves on the Board of Trustees for Mary Lanning Memorial Healthcare in Hastings, Nebraska. He can be reached at michael.allen@marylanning.org. Twitter @WaterWellJournl WWJ February 2016 39 For more information on pumping systems, visit the NGWA Bookstore at www.NGWA.org.