Water Well Journal
Issue link: https://read.dmtmag.com/i/692787
is performed through specialized con- trols that engage the alternate power source and a magnetic clutch mounted on the gear drive. The electric motor, mounted on top of the gear drive, goes along for the ride. Electric motors are generally built in one of two configurations: a vertical hollowshaft or VHS style, where the shaft protrudes up through the motor and attaches to it at the top, or a vertical solid shaft (VSS) style, where the pump shaft is attached to the motor to a per- manent shaft protruding down from the motor. In most cases using VHS motors, the lineshaft from the pump attaches to lengths of lineshaft through the column and then goes through the discharge head and up through the motor where it is attached to the motor through use of a gibb key and adjusting nut at the top. The nut raises the shaft and impellers to the desired clearance. In our example using semi-open im- pellers, the clearance would be calcu- lated to allow for the shaft stretch and an additional allowance so that the im- pellers are operating at their optimum efficiency. In cases using VSS motors, the impeller adjustment is generally conducted in a space between the motor and discharge head with an adjustable coupling. In virtually all instances, the axial (or down) thrust is carried by a thrust bearing in the top of the driver. In our pump example, the driver is a 40 HP, 1800 RPM, vertical hollowshaft (VHS) electric motor. Typically, in most water supply or municipal pumping cases, design of the pump to not exceed the nameplate horsepower of the motor is preferred, although many examples of pumps used for irrigation, industrial, or commercial applications exceed the nameplate horsepower and allow use of the motor's service factor. The service factor varies from horse- power and motor design, but is gener- ally somewhere between a factor of 1.0 (no overload allowed) to a 1.15 rating (15% overload permissible). Electric motors are usually started and run using various methods—the most common being across-the-line or direct starting type or reduced voltage starting. The many available methods of starting and running electric motors will be outlined in a future Water Works column. Although this particular unit uses semi-open impellers, which are not always desirable to use in water well situations, this pump has enough counteracting benefits and is still selected as the basic pump for our example (see Figure 5). In the next installment of The Water Works we will expand upon this selec- tion and examine the system's impact from operating this pump on either a VFD or with a control valve and which is the best option. Until then, keep them pumping! WWJ Ed Butts, PE, CPI, is the chief engineer at 4B Engineering & Consulting, Salem, Oregon. He has more than 35 years experience in the water well business, specializing in engineer- ing and business management. He can be reached at epbpe@juno.com. Correction There was an error in a table in the last installment of The Water Works. In the May issue on page 44, Figure 2 shows three tables. It states Table 3 is showing "shaft elongation in inches per feet of shaft." It should have stated "shaft elongation in inches per 100 feet of shaft." WWJ regrets the error. Figure 5. The selected pump chosen for our "project." WATER WORKS from page 59 waterwelljournal.com 60 July 2016 WWJ