Pump Efficiency Calculations

An approximate method to estimate pump efficiencies is based on the following formula. The expression is valid for flows between 100 and 1,000 gpm, and for developed heads between 50 and 300 ft. 

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Note For single action triplex pump, multiply table value by 0.75. Note Values In the table are calculated tor a pump efficiency of 0.85. Courtesy International Association of Drilling Contractors. 

If the maximum flow-rate required is 20,000 kg/h, calculate the pump motor rating (power) needed. Take the pump efficiency as 70 per cent and allow for a pressure drop of 0.5 bar across the control valve and a loss of 10 velocity heads across the orifice. 

You have purchased a centrifugal pump to transport water at a maximum rate of 1000 gpm from one reservoir to another through an 8 in. sch 40 pipeline. The total pressure drop through the pipeline is 50 psi. If the pump has an efficiency of 65% at maximum flow conditions and there is no heat transferred across the pipe wall or the pump casing, calculate ... 

This figure depends on various assumptions in regard to the piping arrangement, pump efficiency, entrance and exit losses, etc. It is a rough figure, but based on many detailed calculations and is believed to be a reasonable one. 

The equations given in Fig. 6.5a and/or 6.5b can also be applied to an extruder section. In general, however, we do not know the power input to the shafts for an extruder section or, therefore, the specific energy input for this section. The pumping efficiency can be of use here it is determined in advance for the screw geometry in question (measurements taken with a model fluid are adequate, see Section 6.7) or determined by 3-dimensional calculations (as shown in Fig. 6.7). 

A linear relationship not only applies for the pressure characteristic but also for the power characteristic, see Fig. 6.11. For example, the pumping efficiency, Section 6.5.2, can be directly calculated using the dependencies shown. Examples can be found in Chapter 7. The plate-plate model therefore gives a maximum pumping efficiency of 1/3, see Fig. 6.10. 

In example 1, a volume throughput of 300 1/h is pumped at a rotational speed of 300 rpm. Eqs. 7.2 to 7.10 and the typical physical properties of density p=1000 kg/m3 and specific heat capacity c=2000 J/kg-K are used to calculate the back-pressure length, pumping efficiency, energy input and temperature rise in the polymer for the two available screw elements. 

Calculate the piunp shaft horsepower using Equation 5.49 and the pump efficiencies given in Table 5.13. 

Use Equation 8.35 to calculate the shaft or brake horsepower. The pump efficiency, taken from Figure 8.4, is 62%. 

Table 6-3 shows a pump hydraulic design calculation data sheet. Centrifugal Pump Efficiency... 

The computer program PROG62 sizes the centrifugal pump for the given flow rate and fluid characteristics. The program calculates the hydraulic brake horsepower required by the pump and the actual brake horsepower. In addition, the program computes the available net positive suction head (NPSH) and the pump efficiency. Table 6-7 shows the input data and results of the pump hydraulic design calculation. The available NPSH is 64 ft, and the actual brake horsepower required for the pump operation is 7.0hp, with a pump efficiency of 68%. 

Using the affinity law (Equation 6-76), the corresponding values for the head at varying flow rates are shown in Table 6-8. The computer program PROG63 calculates both the brake horsepower and pump efficiencies of the 6- and 8-inch pumps. Tables 6-9 and 6-10 show the input data and the computer results of these pumps. The characteristic curves are shown in Figure 6-6. 

THIS PROGRAM CALCULATES ALL PUMP HEAD CALCULATIONS REQUIRED TO WRITE A PUMP SPECIFICATION SUITABLE FOR A VENDOR INQUIRY OR PURCHASE ORDER. THE PROGRAM FURTHER CALCULATES THE CENTRIFUGAL PUMP EFFICIENCY AND PUMP HORSEPOWER USING AN EQUATION DEVELOPED BY BY C. BRANAN (The Process Engineer s Pocket Handbook, Gulf Publishing Company, Houston 1976.)... 

FOR HBHP CALCULATION, ASSUME PUMP EFFICIENCY .0) PUMP EFFICIENCY (%). 

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