Water Well Journal
Issue link: https://read.dmtmag.com/i/692787
N ow that we have taken the first step towards designing our hypothetical pump installation, it is time to deter- mine the exact bowl and pump manufacturer we wish to use. Unlike many 4″ submersible pumps, a vertical turbine pump is not a commonly available "off the shelf" item. It's a type of pump that requires a specific design process and selection that may change from one manufacturer to another. We'll take the design information we obtained in the May Water Works column and apply it to the actual selection of the pump for our "project." Disclaimers: The proper application of vertical turbine pumps as well as submersible pumps is a specialized engi- neering task that requires consideration of many individual factors. The reader is cautioned to exercise appropriate judg- ment in the use and application of the following information, seek technical assistance whenever warranted, and follow all manufacturers' guidelines, especially when considering deep well applications, as well as follow all application and instal- lation specifications. Please remember this column is mainly directed towards personnel concerned with the proper design of a vertical tur- bine pump, not necessarily which brand it is. Although many brands of pumps are intended only for representation and sale by specific dealers, this more often applies to smaller and mid-size submersible pumping units in horsepower from 1/2 HP up to 60 HP. When examining a vertical turbine pump application, although the choices are much more limited to fewer manufacturers, most will welcome a possible sale. For those other brands of vertical turbine pumps that are repre- sented by a specific dealer network within a geographic region, the designer should still strive to investigate all the various brands of pumps available within the market area and select the unit best suited to the application. With all that said, however, I have been in this business long enough to recognize a salesman may not be the same as a designer and may try to push a certain make and model of a pump to the customer even though the pump may not totally satisfy all of the conditions. In these cases, I have witnessed pumps being used that operated away from the best efficiency point, and in some cases, some even far outside of the best efficiency window. As I previously stated, this column is directed to the indi- vidual most concerned with the proper design and application of a vertical turbine pump, regardless of brand, and the steps to be taken to make sure the client ends up with the right pump. Vertical Turbine Bowl Selection The final selection of a vertical turbine pump (VTP) is not simply performed through a knowledge of the design condi- tions, i.e., capacity against total dynamic head alone. In addi- tion, it is just as critical the designer understand and factor in the specific application, and the projected hours per day and days per year of operation. Likewise, in this new world of variable speed or flow pumps, how much time each day the unit is projected to operate at reduced speed or flow, at what capacity and head, and if operation at reduced speed or flow could compromise the efficiency and life span of the unit, if it is to be used in that fashion. This may appear to be quite a laundry list of concerns. But if the job is to be done right, all these factors should be con- sidered, particularly those surrounding variable speed or flow operation. This factor becomes a very important element of the pump's performance and projected life, especially if oper- ation at reduced speed will push the pump into a prolonged "critical speed" or excessive head performance. Finally, in order to effectively select a VTP it is critical the designer have an understanding of the advantages, disadvan- tages, strengths, and limitations of the various brands and units available for the job—including the driver, most often an electric motor. If any of these factors are pertinent to the de- sign, the designer should find a way to express these concerns to the client without appearing unnecessarily biased in favor of or against a specific make of pump. In our pump example, our client has thrown us a curve ball even though we were originally told to assume a variable fre- quency drive, or VFD, would be used for the reduced flow conditions. Now he has informed us he would also like to consider use of a control valve. Once we are reasonably sure of the primary capacity/head conditions (500 GPM at 260′ TDH [total dynamic head]), it is time to move onto the two alternative design conditions. ED BUTTS, PE, CPI THE WATER WORKS ENGINEERING OF WATER SYSTEMS Part 13—Vertical Turbine Pump Design (2) It is critical the designer understand and factor in the specific application , and the projected hours per day and days per year of operation. waterwelljournal.com 54 July 2016 WWJ