CORNELL AGRICULTURAL PUMPS BEST IN CLASS EFFICIENCY
ECONOMICAL CLEAR LIQUIDS PUMPS
percent from 850 to 1,100 gpm and is 83 percent at 750 gpm. Pump 2 would be a much better choice.
How many pumps to choose? An operator may pick one pump for his entire system and let the VFD control it over a wide variety of flows. If you have a system with widely varying flows but want to keep the pressure constant, you would look for a flat pump curve like pump 3. If pump 3 was selected for flows from 1,000 to 3,000 gpm (240 feet TDH), it could accomplish that outcome, and the speed would only vary from 1,800 to 1,630 rpm. At 3,000 gpm, the pump efficiency is good (>86 percent), but at 1,000 gpm it is well below 70 percent. We can’t even estimate it. If the system operates at lower flows a majority of the time, this would not be a good choice from an energy savings standpoint. Two pumps in parallel that operate efficiently from 1,000 to 1,500 gpm would be better. If energy use is not an issue, the operator may still choose a one-pump system for its simplicity, but two pumps would be more efficient and part of the system could still be operated if one pump is down for repairs.
In conclusion, don’t use VFDs as an easy way out when designing your pumping system. Understand where you are on each pump curve for all of the possible flow scenarios. If predicting energy use is a priority, obtain accurate data regarding how often the system operates at various flows.
Len Ring, MSc, PE, CID, is an agricultural engineer who has been involved with irrigation in western Canada for over 40 years. He currently operates Ring Irrigation Engineering, specializing in the design of on-farm irrigation systems, pipelines and pumping stations. Ring was the author of Chapter 8 “Irrigation Pumping Plants” in the Irrigation, Sixth Edition textbook.
CLOSE COUPLED, FRAME MOUNT, AND ENGINE MOUNT OPTIONS
RENOWNED CORNELL QUALITY AND DEPENDABILITY
FLOWS TO 10,000 GPM, HEADS TO 800 FEET OVER 70 YEARS EXPERIENCE DURABLE CONSTRUCTION
DOUBLE VOLUTE, HYDRAULIC BALANCE LINE
CORNELL PUMP COMPANY | CLACKAMAS, OR 97015 USA
WWW.CORNELLPUMP.COM | P: +1 (503) 653-0330 | F: +1 (503) 653-0338
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