Centrifugal pumps performance curves

The majority of centrifugal pumps have performance curves with the aforementioned profiles. Of course, special design pumps have curves with variations. Eor example, positive displacement pumps, multi-stage pumps, regenerative turbine type pumps, and pumps with a high specific speed (Ns) fall outside the norm. But you ll find that the standard pump curve profiles are applicable to about 95% of all pumps in the majority of industrial plants. The important thing is to become familiar with pump curves and know how to interpret the information. 

Power consmnption the operating point of centrifugal pump should be chosen at the highest efficiency possible. Generally, the vendors/manufacturers offer a range of models, which cover the requirements of capacity, head, etc. However, the final selection should be done while keeping in mind the most likely (normal) condition in which the pump will be ran. In case of positive displacement pumps the performance curves should be studied to select proper speed for the capacity and required head... 

Figure 3-36A illustrates typical manufacturers performance curves for centrifugal pumps as a function of capacity. 

It is important to recognize that a centrifugal pump will operate only along its performance curve [10, 11]. External conditions will adjust themselves, or must be adjusted in order to obtain stable operation. Each pump operates within a system, and the conditions can be anticipated if each component part is properly examined. The system consists of the friction losses of the suction and the discharge piping plus the total static head from suction to final discharge point. Figure 3-51 represents a typical system head curve superimposed on the characteristic curve for a 10 by 8-inch pump with a 12-inch diameter impeller. 

For onshore facilities, water may be supplied from local public water mains, storage tanks, lakes and rivers. In these cases a conventional horizontal pump is used. The preferred design for onshore fire water pumps is a horizontal centrifugal type with a relatively flat performance curve (i.e., pressure versus quantity). The discharge pressure is determined by the minimum residual pressure required at the most remote location of the facility flowing its highest practical demand with allowances added for piping friction losses. 

If the characteristic performance curves are available for a centrifugal pump operating at a given rotation speed, equations 4.28 to 4.30 enable the characteristic performance curves to be plotted for other operating speeds and for other slightly different impeller diameters. 

Figure 7.3. Performance curves of single-suction impellers corresponding to two values of the specific speed, (a) Ns - 1550, centrifugal pump, (b) Ns = 10,000, mixed and axial flow pumps.

P7. AJAX PUMPS Technical Data E Range Back-Pull-Out Centrifugal Pumps. Performance Curves E Range Back-Pull-Out Centrifugal Pumps. 

Related Calculations. Use the method given here for any type of pump whose variables are included in the Hydraulic Institute curves (Figs. 6.10 and 6.11) and in similar curves available from the same source. Operating specific speed, computed as above, is sometimes plotted on the performance curve of a centrifugal pump so that the characteristics of the unit can be better understood. Type specific speed is the operating specific speed giving maximum efficiency for a given pump and is a number used... 

Figiue 5.28 shows typical performance curves for a centrifugal pump. The puitp manufacturer supplies these curves for water. When a control valve in the pump discharge opens or closes, the pump will follow these performance curves. 

Base Mounted Centrifugal Pump Performance Curves, Curve Booklet B-260E, Bell Gossett ITT, Fluid Handling Division, Morton Grove, IL, 1987. 

A centrifugal pump is used with a performance curve that can be approximated by the relationship... 

Figure 9.19 Performance curves and control characteristics of pumps, (a) Differential pressure Ap as a function of volumetric flow rate V. Curves Ca and Cb are performance curves for a centrifugal pump at rotation rates /ia and /Ib respectively. Curve 0 is for a reciprocating pump. Curves a and b give the installation characteristic for the operation points A and B. (b) Volumetric flow rate (delivered by reciprocating pump) as a function of stroke frequency, /i, at constant stroke length hp or of stroke length at constant stroke frequency.

Centrifugal pumps are used in a variety of applications and are available from many manufacturers. Purtp impellers may have forward or backward vanes, may have enclosed or open configurations, and may operate at different speeds. Their performance characteristics depend on their mechanical design. As a result, experimentally determined performance curves are supplied routinely by the punp manufacturer. 

Figure 18.11 shows the performance curve for a centrifugal conpressor. It is immediately observed that the y-axis is the ratio of the outlet pressure to inlet pressure. This is in contrast to punp curves, which have the difference between these two values. Curves for two different rotation speeds are shown. As with punp curves, curves for power and efficiency are often included but are not shown here. Unlike most pumps, the speed is often varied continuously to control the flowrate. This is because the higher power required in a conpressor makes it economical to avoid throttling the outlet as in a centrifugal punp. 

Figure 41.3 is similar to a centrifugal pump performance curve in regard to its shape. That is, it has a relatively flat portion of its curve and a relatively steep portion of its curve ... 

Figure 1, Influence of net positive suction head on a characteristic single stage, centrifugal pump performance curve (H O at 70 F)... 

The Operating System. Regardless of calculated centrifugal compressor performance, the machine will operate only on or along its operating curve to fit the system of which it is a part. This is quite similar to the system performance of a centrifugal pump. Friction, other pressure drops of the system, and how friction varies with operating conditions determine machine performance. 

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