Water Well Journal

January 2017

Water Well Journal

Issue link: http://read.dmtmag.com/i/767379

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Page 32 of 63

W ith regard to pumping from a deep well, there has probably been no more worthwhile and valuable improvement over the past 50 years than the sub- mersible pump. This type of pump combines the concept of a multi-stage vertical turbine pump, using an axial/mixed flow design, with a multi-horsepower and phase electrical motor designed to op- erate under hundreds of feet of water. This enables a reason- ably low-cost and efficient lifting of water from water wells sometimes thousands of feet deep. In the next three installments of The Water Works we will shift gears somewhat and vary our previous discussions of using a vertical turbine pump (VTP) to outline the alternate and currently popular method of using submersible pumps to deliver water for municipal, irrigation, industrial, commercial, and general water supply applications. Disclaimer: The proper application of larger horsepower submersible pumps is a specialized engineering task requiring consideration of many individual factors, particularly the elec- trical power supply. The reader is cautioned to exercise appro- priate judgment in the use and application of the following information, seek technical assistance whenever warranted, and follow all manufacturers' guidelines—especially when considering very deep well or large horsepower applications. Please also follow all application and installation specifica- tions and recommendations and all applicable regulatory codes. Submersible Pump Concepts The use of a submersible pump to deliver water and other fluids from deep wells, possibly thousands of feet deep, is not a new or unknown concept. This method of pumping has been in widespread use to date for more than 75 years and has over- taken the use of VTPs for many common potable water appli- cations in recent years. Other than the typically higher operating speed of 3600 RPM, the principle behind the use of a submersible centrifu- gal type of pump, equipped with several stages of individual impellers and diffusers commonly assembled in a single stack, closely mirrors many of the design and construction features of a VTP. Submersible pumping units for commercial, industrial, irri- gation, and municipal potable water supply are now available in capacities from just a few gallons per minute to more than 10,000 GPM; heads (TDH) that range from 50 feet to more than 1000 feet; motor and pump design speeds from less than 1200 RPM up to 3600 RPM; voltages from 240 volts single phase to more than 4600 volts three phase; motor horsepower from 3 HP to more than 2000 HP; pump and motor unit diam- eters from 4 inches to more than 24 inches; and discharge assemblies including several that are below and above ground configurations (Figure 1). It is easy to see almost any conceivable freshwater and wastewater applications can be fitted with a submersible pump. The basic hydraulic design of each pump is virtually iden- tical using the well-known concept of multiple stages of com- bined impeller/diffuser assemblies with many of the smaller diameter (6-inch and 8-inch) VTP bowl assemblies undergo- ing modifications at twice their originally intended design speed for submersible applications. Thanks to the affinity laws, these units are now commonly used for the higher capacity, head, and horsepower require- ments found in many deeper or smaller diameter wells. There are various design factors associated with the successful de- sign of a submersible pump for larger applications and we will detail each one separately. Preliminary Design (Basic Pump Selection) Just as with a vertical turbine pump, the preliminary selec- tion of the pump and motor, based on the limitations of the source and available power, is generally the first step to take with a larger submersible pump installation as well. Knowledge of the inherent Conditions of Service (COS) in capacity and head is critical information needed by the de- signer throughout the entire design phase, but particularly im- portant when initially evaluating the possible size range of the prospective pump and motor. Although a working knowledge of the source, usually a water well, is also vital, the COS is generally accepted as the most important single factor to initially understand if the job can even be done. ED BUTTS, PE, CPI THE WATER WORKS ENGINEERING OF WATER SYSTEMS Part 14(a)—Submersible Pump Design, Part 1 WATER WORKS continues on page 32 Knowledge of the inherent conditions of service in capacity and head is critical information needed by the designer throughout the entire design phase. Twitter @WaterWellJournl WWJ January 2017 31

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