Module 3: Use of the PumpBaseTM Software
Use of PumpBase™ Software
Use of PumpBase™ Software
Use of PumpBase™ Software
Use of PumpBase Software from the CD-ROM in the Solutions Manual PumpBase TM is a copyrighted software package developed by Tahoe Design Software Company of Truckee, California. See their web site at http://www.tahoesoft.com/. PumpBase TM provides performance curves for thousands of commercially available pumps, and it has the ability to search for suitable pumps to satisfy your requirements for total head on the pump and pump capacity (flow rate). It is a powerful supplement to the pump performance curves included in the book in Chapter 13, Figures 13.23 to 13.31. This software package is very useful when assignments or design projects require students to select a suitable pump for a given application. The author has used it quite successfully in design projects as described in Module 4 of this website. The purpose of this module is to summarize the capabilities of PumpBase TM and to describe how it is used.
Primary Function of PumpBaseTM Software The primary function of the software is to assist the user in selecting a suitable pump for a given application. It will then provide detailed data for the operating point of the pump in a given fluid flow system.
Summary of Fluid Flow System Design Process with Pump Selection Section 13.9 in Chapter 13 of the text explains the general method for designing a fluid flow system, including the selection of a pump. The following steps are typical. 1. Propose the general layout of the system. Include the location of the source of the fluid, the pump location, the location of the discharge point, the nature of the piping system, the types and sizes of valves and fittings, and the values of any specified pressures. 2. Specify the sizes for all pipes. You may use Table 6.3 in Chapter 6 as a guide to specify pipe sizes that produce reasonable flow velocities in the system. 3. Determine the equation for the total head on the pump,
, at the desired operating conditions using the energy equation.
4. 5. 6. 7.
Evaluate all energy losses at the desired flow rate and complete the calculation of the total head on the pump, . Specify a suitable pump that will deliver at least the desired flow rate when operating at the computed total head. Acquire the performance curve for the selected pump. Create the system curve, a plot of the total head as a function of the volume flow rate. See Figure 13.35 in the text. Determine the operating point of the pump by superimposing the pump rating curve on the system curve and observing where they intersect. See Figure 13.36 in the text. The operating point is typically close to the desired conditions, but often a higher flow rate will result. 8. Determine the performance of the selected pump at the operating point. Typically required are the actual flow rate delivered, the actual total head at this flow rate, the power required to drive the pump, the efficiency, and the net positive suction head required ( ). 9. Provide for the installation of the selected pump into the system. This may require reducers or enlargements if the suction or discharge fittings are of different sizes than those of the suction and discharge piping. Gradual reducers and enlargements are preferred as discussed in Chapter 10 on Minor Losses. 10. Ensure that the NPSH available at the pump inlet is greater than the NPSH required by the pump. PumpBase software assists in Steps 5–10 of this process.
Example of the Use of PumpBase Software System Data Required. Refer to Section 13.9 on pages 390–395 of the text for a review of the process of selecting a pump for a given fluid flow system. Example Problem 13.3 shows an example of that process to select a suitable pump for the system shown in Figure 13.33 on page 392. A pump is to be selected to raise water at 60°F from a lower vented reservoir to an elevated pressurized tank. The piping system includes energy losses from several elements: pipe friction, valves, elbows, and entrance and exit losses. The total energy loss was computed in the spreadsheet (Figure 13.34) to be 139 ft. The total head on the pump is then comprised of the following (see Steps 3 and 4, pages 392–393): The elevation head difference of
= 80.0 ft from the source to the upper tank.
The pressure head difference of = 80.77 ft where The total energy loss in the system of 139 ft.
= 35.0 psig and
= 0 psig.
Then the total head on the pump is = 80.0 ft + 80.77 ft + 139 ft = 299.8 ft. In PumpBase, the total head is called the total dynamic head, or TDH. This reflects the fact that it includes the effects of the velocity head for the flow and the energy losses that are, in turn, dependent on the velocity head. But the TDH also includes the static head, , comprised of the elevation head and the pressure head that must be produced by the pump even when there is no flow. See Figure 13.35 in the text on page 395. In this example,
= 80.0 ft + 80.77 ft = 160.8 ft
Thus the primary data required to select the pump are listed here with the values for this example: Required flow rate = Q = 225 gal/min = 225 gpm Total dynamic head = TDH = Total static head =
= 299.8 ft
= 160.8 ft
Operation of PumpBase. Use the CD-ROM and open PumpBase. The data entry window will appear. Then follow these steps: Fill in the data boxes labeled TDH, Flow, and Static Head. These are the minimum data required as discussed above. In this window, it is also necessary to check the box labeled Fit to a 2 nd degree curve. This causes the software to define the complete system curve by fitting a 2 nd degree curve between the static head, , and the total dynamic head, TDH. This is appropriate because the system curve is the sum of the static head and the dynamic head for any flow rate. See Figure 13.35 on page 395 of the text. The curved part of the system head curve reflects the fact that the dynamic head is proportional to the velocity head,
. Recall that all energy losses are found by multiplying some resistance coefficient times the velocity head of the flow for each element. Therefore,
the energy losses are proportional to the velocity squared. This justifies the use of the 2 nd degree curve. Optional data can be entered for NPSH available. If entered, the program would screen candidate pumps to ensure that the NPSH required by the pump is less than the value of NPSH available. See Section 13.12 of the text for guidance on how to compute NPSH. Let's omit that data for now. The NPSH required by the pump will be reported for each candidate pump so you can check it later. Also, the program allows you to specify features of the pump to be selected such as the orientation of the pump (horizontal, vertical, in-line), the type of application (fire protection, well, trash handling and so forth), and other features (portable, submersible, corrosion resistant). This is done by selecting the Selection Criteria button. For simplicity, let's also omit that information at this time. You must note that the basic pump performance data are related to its operation when pumping water at 60°F, a standard for the pump industry. That is what we have in this example problem. If some other fluid is used, its properties can be entered in a special section of the input data screen called Liquid Properties. Then correction factors for viscosity, specific gravity, and vapor pressure can be applied to the basic pump performance data. At this time, you should select the button called Search Database. This will cause the program to take your data and use them as screening factors to select pumps that meet your design requirements. However, you must retain responsibility to evaluate all performance data for the selected pump. There are times when a pump listed does not satisfy requirements. After the search is completed, a message at the bottom of the input window will tell how many pumps were selected. At that time, you could choose to limit the selection further and rerun the search. When you are satisfied with the search results, select the button called View Pumps. The selected pumps will be listed in the order of efficiency. You should then examine the detailed performance data for each candidate pump. In general, you should favor the most efficient pump provided it meets other design and installation requirements. Highlight one of the selected pumps and then select the button called Plot Pump. The performance curves for the selected pump will appear. See the sample in Figure 1 of this module. They look very similar to those shown in the text in Figures 13.23 to 13.31. Superimposed on the performance curve is the system curve that represents the relationship between total head and flow. The intersection of the system curve with one of the pump head curves is the operating point of that pump in the system you are designing. Symbols show the design point (based on your input data) and the operating point. You should ensure that the operating point is beyond the design point, guaranteeing that the pump will be able to deliver at least your required flow rate against the system head. Recall that a given pump can have different sizes of impellers installed. The pump performance data typically show a variety of impeller diameters between the maximum and minimum sizes. Manufacturers often provide standard increments of impeller diameter. In the example shown in Figure 1, at the upper left, this manufacturer offers impellers from 8.0 inches to 10.5 inches in increments of 0.125 in.
FIGURE 1. Performance curve for a 3x2x10.5 centrifugal pump with impeller diameter of 9.5 in. Intersection of system curve and pump curve shows operating point. Design point also shown. Operating results listed to right of pump curve. Basic data for pump listed at top left of page. The operating point is taken to be where the system curve intersects the next larger impeller diameter beyond the design point. That impeller size will be identified on the curves and also listed in the Operating Results area to the right of the curves. The selected pump has a diameter of 9.50 inches. Manufacturers of some of the pumps in the database allow virtually any impeller size to be ordered. In such cases, the design point and the operating point are coincident and the impeller diameter is computed and reported in decimal inch form. An example is shown in Figure 2.
FIGURE 2. Performance curve for 2x1.5x9.6 centrifugal pump. Impeller diameter is trimmed to 8.892 in so that operating point is coincident with design point. Operating results for flow and TDH are equal to design conditions. Also listed alongside the pump performance curves are all necessary performance data for the pump at the operating point. The most important are the following with values given for the selected pump shown in Figure 1: ◊ The actual flow rate Q = Flow = 228.1 gpm ◊ The actual TDH at that flow rate
TDH = 303.9 ft
◊ Pump efficiency
Efficiency = 57%
◊ Impeller diameter
Imp. Dia. = 9.5 in
◊ NPSH required
= 12.03 ft
◊ Power required to operate the pump
Power = 34.6 bhp (Brake horsepower) Also note, as stated in Step 5 on page 393 of the text, that the American National Standards Institute (ANSI) and the Hydraulic Institute (HI) call for selecting pumps that fall in the preferred operating region (POR) within the range of 70% to 120% of the best efficiency point (BEP) for the pump. Note that the selected pump operates virtually right on the BEP for this pump with a 9.5 in impeller. Other data shown for the pump are listed in the upper left area. Some of them are discussed below. The suction and discharge port sizes are shown. You should plan your installation accordingly, adapting the sizes of your suction pipe and discharge pipe to fit. Enlargers or reducers may be required. Figure 7.1 on page 192 shows an installed pump with a reducer on the suction side and an enlarger on the discharge side. The operating rotational speed of the pump is given. For this example, the speed is 3550 rpm. This is a typical speed for pumps driven directly by a two-pole electric motor operating on the 60 Hz electric power used in the United States. Another typical speed is 1750 rpm, the full-load speed for a four-pole motor.