Pumps Irrigation and Drainage Engineering pp 147-167 | Cite as Peter Waller (1) Muluneh Yitayew (1) 1. Agricultural and Biosystems Engineering, University of Arizona, Tucson, USA Chapter 2.2k Downloads

Abstract Selecting a pump is generally the last step in an irrigation system design. The pump is selected based on the required flow rate and pressure requirements of the irrigation system. The most common pumps used in sprinkler and drip irrigation systems are centrifugal pumps. Pump selection is generally a process of looking through pump catalogs and selecting the pump with highest efficiency at the required flow rate and pressure. The process also includes motor power selection, calculation of the net positive suction head, and possibly trimming the impeller in order to fine-tune the pump to the irrigation system requirements. The affinity laws govern the relationships between impeller diameter, motor frequency (RPM), flow rate, and pressure. The flow rate and pressure relationship for a given impeller diameter is called the pump curve. Pump curves and irrigation system curves can be mathematically combined in order to find the operating pressure and flow rate of the system. There are several possible sources of energy for pumps. The costs of three energy sources (solar, diesel, and electric) are compared in an example. Finally, the chapter covers basic principles of chemigation injection system design. Designing the pump station correctly is an essential final step in the provision of a reliable source of water.

Keywords Pump types Performance curves System curves Affinity laws Total dynamic head This is a preview of subscription content, log in to check access.

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Questions 1. 1. The revolutionary speed of electric pumps is slightly less than divisors of 3600. Typical pump rpm’s are 875, 1750, and 3500. Why are most pumps manufactured with these revolutionary speeds? 2. 2. What would be a typical TDH for a centrifugal pump with flow rate 1,000 m3/hr based on the typical specific speed for a centrifugal pump? Recalculate for pump flow rates of 100 m3/hr and 10 m3/hr. What type of pump would be appropriate for a very high flow rate and very low head? 3. 3. Using the equations for the relationships between power, flow rate, and head, describe the shape of the head/capacity curve if efficiency was constant over a range of flow rates? 4. 4. Verify that the water horsepower generated by the 5.9375 impeller curve in Fig. 9.4 corresponds with the efficiency and brake horsepower (the curve below the head capacity curve). Calculate at the point of highest efficiency. 5. 5. Describe the relationship between efficiency and flow rate in Fig. 9.4. 6. 6. An irrigation system requires 600 gpm and 160 ft head. Select the best impeller for this application on the B4JPBH (Fig. 9.5) pump curve. 7. 7. What is the maximum allowable flow rate of a B4JPBH pump (Fig. 9.5) with a 12 3/8² impeller and a 40 HP motor? What is the maximum flow rate for the 50 HP motor with the same impeller? 8. 8. An irrigation system requires TDH=168 ft and Q=600 gpm. Select an impeller diameter (trimmed if necessary) and select a motor HP with the B4JPBH pump. 9. 9. The 16BZ pump (Fig. 9.7) with a 5¾² impeller is used to run a sprinkler system. There is a 2 m pressure loss in pump fittings and filters. Find the operating point. Plot the two curves and verify that the calculated point is the correct point. The 5¾² head-capacity curve and the irrigation system curve are: \begin{array}{l}\mathrm{T}\mathrm{D}\mathrm{H}\left(\mathrm{m}\right)=-0.00170{\mathrm{Q}}^2+0.0743\mathrm{Q}+43.76\hfill \\ {} {\mathrm{Q}}_{\mathrm{system}}\left({\mathrm{m}}^3/\mathrm{h}\right)=14.175{\left({\mathrm{H}}_{\mathrm{system}}\right)}^{0.531}\hfill \end{array} 10. 10. In Example 9.6, change the elevation of pivot 2 to 100 m elevation and pivots 3 and 4 to 120 m elevation. Select the pump operating pressure. Each pivot requires 100 L/sec. Determine the number of pumps, flow rate, and TDH of the pump station. Discuss options to reduce energy. 11. 11. A variable speed pump controller is used to vary the flow rate of the 16BZ pump with the 5 3/4² impeller. The revolutionary speed is lowered from 3500 to 3000 RPM. The system curve is Qsystem (m3/h)=14.175 (H system)0.531. There is 3.5 m head loss in the pump fittings and filters. Find the operating point TDH and flow rate. 12. 12. Imagine that a new technology was developed that enabled farmers to produce biodiesel from crop residue. The biodiesel production unit has a capital equipment cost of $50,000; a labor, maintenance, and energy cost of$0.30/L, and produces 15,000 L of biodiesel per year. Calculate whether this would be a less expensive alternative than the electric pump system in Example 9.9. Use the Fuel and pump costs worksheet in Chapter 9 Excel program. 13. 13. Redo Example 9.9 with a solar powered pump. Based on the cost of materials and the service life and replacement cost of solar components, the solar panel array provides electrical energy at a cost of $0.08/kW-hr for the 20 year project life. The solar pump can only be used during daylight; thus a larger pump is required and a reservoir must be constructed for storage. Increased capital cost of hydraulic components is$50,000 and replacement and maintenance costs remain the same as Example 9.9. Recalculate if carbon credits for the system are worth $1,000/yr. 14. 14. A pump sucks water from a canal and discharges to a reservoir 100 m above the canal. Pump station valves and fittings are the same as in Example 9.11 except that the pipe diameters are 6², 3², 2.5², and 4² instead of 4², 2², 1½², and 3². Two other changes are that the eccentric angle is 50° and the cone angle is 40°. Flow rate is 20 L/sec. All pump station pipe is 6 gage steel, and the mainline pipe is 4² SCH 40 and is 500 m long. Assume an open discharge to the upper reservoir. Calculate the pump TDH required. Show calculations for the pressure loss in the eccentric reducer and the concentric cone. Calculate the percent of required TDH due to pump station losses, and the percent of total friction loss that is due to pump station losses. (Use worksheet) 15. 15. Redo question 15, but discard the eccentric, and let the suction pipe be all 75 mm (3 in. pipe. Second, use a bushing on the discharge side (sudden expansion) rather than a cone expansion. Determine which change results in the greatest increase in head loss. 16. 16. Use the 16BZ pump with 5 3/4² impeller (M) to deliver water to the upper reservoir for the system shown below. Select pipe diameters equal to 6², 4², 3², and 4² for the four pump station pipe sections. Use 4² Schedule 40 PVC for the mainline, which is 493 m long. Draw a system curve (develop with Centrifugal pump fittings worksheet by inputting different flow rates and corresponding TDH requirement) and pump head-capacity curve based on Fig. 9.6. Find an exponential equation for the system curve and equation for the head-capacity curve, and calculate the point of intersection (operating point) for the system 17. 17. Venturi injectors are designed based on the principle that if water velocity increases, then pressure decreases as shown by the Bernoulli equation. A narrow throat increases the velocity at the suction point. Concentric cones are used to gradually increase flow rate to the throat and decrease flow rate from the throat. Based on what you know about concentric cones, draw a Venturi injector geometry that has minimum head loss. 18. 18. Some people recommend creating the pressure differential across a Venturi by restricting mainline flow. It is a much better idea to have a separate centrifugal pump provide the pressure differential, as shownin this example. Mainline flow rate is 200 L/sec, and Venturi flow rate is 0.90 L/sec. Venturi injection time is 1,000 hours per year. The required pressure differential across the Venturi is 283 kPa. The cost of energy is$0.10/kW-hr. Calculate the energy cost per year for providing the required pressure differential across the Venturi by constricting the mainline flow with a valve. Calculate the energy cost of using a centrifugal pump in the bypass line to provide the pressure differential needed by the Venturi. 19. 19. How could a Venturi be used within a pump to lift groundwater up to the surface in a well. (Hint: look up jet pumps). 20. 20. Calculate throat pressure (gage pressure and absolute pressure) and discharge pressure in a Venturi injector that that has a 30 mm internal diameter at both ends and that has a flow rate of 0.9 L/sec. The length of the entire Venturi is 15 cm and the length of the throat is 2 cm; however, assume that the equivalent length of the throat is 10 cm due to flow entering the throat through the suction tube. The upstream pressure is 300 kPa. The reducer cone angle (inlet side), , is 30°, and the expansion cone angle (discharge side) is 15°. Assume that Hazen-Williams C in the throat is 100. The inside diameter of the throat is 7 mm. 21. 21. Redo question 20 but optimize the inlet and discharge angle in order to minimize pressure loss across the Venturi. Keep the same throat dimension and Venturi length. Derive an equation based on the geometry of the system that calculates discharge angle as a function of inlet angle.

References Beard R, Robert Hill (2000) Maintaining electric motors used for irrigation. Utah State University Cooperative Extension. ENGR/BIE/WM/06 http://extension.usu.edu/files/publications/publication/ENGR_BIE_WM_06.pdf (http://extension.usu.edu/files/publications/publication/ENGR_BIE_WM_06.pdf) NRCS (1997) Energy use and conservation. National Engineering Handbook. Part 652. Chapter 12. http://www.irrigationtoolbox.com/NEH/Part652_NationalIrrigationGuide/ch12.pdf (http://www.irrigationtoolbox.com/NEH/Part652_NationalIrrigationGuide/ch12.pdf) NRCS (2010) Variable Speed Drive (VSD) for irrigation pumping, engineering technical note MT-14. http://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/nrcs144p2_054026.pdf (http://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/nrcs144p2_054026.pdf) Huffman R, Fangmeier D, Elliott W, Workman S (2013) Soil and water conservation engineering. American Society of Agricultural and Biological Engineering Google Scholar (http://scholar.google.com/scholar? q=Huffman%20R%2C%20Fangmeier%20D%2C%20Elliott%20W%2C%20Workman%20S%20%282013%29%20Soil%20and%20water%20conservation% 20engineering.%20American%20Society%20of%20Agricultural%20and%20Biological%20Engineering)

About this chapter Cite this chapter as: Waller P., Yitayew M. (2016) Pumps. In: Irrigation and Drainage Engineering. Springer, Cham DOI (Digital Object Identifier) http://doi.org/10.1007/978-3-319-05699-9_9 Publisher Name Springer, Cham Print ISBN 978-3-319-05698-2 Online ISBN 978-3-319-05699-9 eBook Packages Earth and Environmental Science About this book Reprints and Permissions

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Pumps Irrigation and Drainage Engineering pp 147-167 | Cite as Peter Waller (1) Muluneh Yitayew (1) 1. Agricultural and Biosystems Engineering, Univer...

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