Pump performance curves

Pump performance curves are the least used, least consulted, least appreciated, and least understood aspect of the world of industrial pumps. The plant personnel who most need their pump curves, meehanics and operators, generally don t have the curves and accompanying information at their disposal. The people who control the performance curves store them in a file, in a drawer, in a cabinet that s almost never opened. They don t share the information contained in the curves with the people who need it. Maybe it s because they themselves don t understand the information to share it. In the next few paragraphs and pages, we re going to explain the pump performance curves. This might be the most important chapter of the book. 

In reality, the performance curve is easy to understand. It isn t rocket. science. The performance curve indicates that the pump will discharge a certain volume or flow (gpm) of a liquid, at a certain pressure or head (H), at an indicated velocity or speed, while consuming a specific quantity of horsepower (BHP). The performance curve is actually four curves relating with each other on a common graph. These four curves are  

The Pump s Minimum Rec]uirement Curve. Its ealled Net Positive Suction Head required, NPSHr. 

Think of the pump curve like the dashboard or control panel of a car. No one would operate a car without the dash instrumentation panel. 

The information on the dash panel is located right in front of the eyes of the operator of the ear. It s a shame that most pump operators don t have their control panel (the curve) before their eyes, or even within reach, as they operate the pumps. This is the source of many problems with pumps. 

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FIG. 10-31 Typical pump performance curve. The curve is shown for water at 85 F. If the specific gravity of the fluid is other than unity, BHP must he corrected. 

The same procedure maybe used at other pump flows to permit plotting the series of balance-point curves as has been done in Fig. 29-61. From such curves, one can establish the maximum lean pump at any total tower outflow, and combining this with the semilean-pump performance curve results in Fig. 29-55. Bypass flow plotted in Fig. 29-55 is obtained by adding simultaneous lean- and semilean-pump flows and subtracting the recovery pump-turbine flow required to make the balance point at that lean-pump flow. 

Some pump companies will promote and tout their low Nss values. Sometimes a specification engineer will establish a maximum Nss limit for quoted pumps. Let s consider the.se examples of operating parameters of pumps, and determine the Nss. These values are lifted from the pump performance curves at the BLP. 

Now the pump selected reads NPSHr on its pump performance curve of 12 feet for cold water ser dce. 

An oil with a 32.6° API gravity at 60°F is to be transferred from a storage tank to a process unit that is 10 ft above the tank, at a rate of 200 gpm. The piping system contains 200 ft of 3 in. sch 40 pipe, 25 90° screwed elbows, six stub-in tees used as elbows, two lift check valves, and four standard globe valves. From the pump performance curves in Appendix H, select the best pump to do this job. Specify the pump size, motor speed, impeller diameter, operating head and efficiency and the horsepower of the motor required to drive the pump. 

For quick pump selection, manufacturers often give the most essential performance details for a whole range of pump sizes. Figure 10-40 shows typical performance data for a range of process pumps based on suction and discharge pipes and impeller diameters. The performance data consists of pump flow rate and head. Once a pump meets a required specification, then a more detailed performance data for the particular pump can be easily found based on the curve reference number. Figure 10-41 shows a more detailed pump performance curve that includes, in addition to pump head and flow, the brake horsepower required, NPSH required, number of vanes, and pump efficiency for a range of impeller diameters. 

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

FIGURE 1.2 Pump performance curves for AJAX E range pump E32-20. (Reproduced with permission.)... 

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

The plotted values agree well with reported values from pump-performance curves, especially over the range ... 

Heavy metal oxide slurry is to be pumped at a volumeUic concentration of 18%. The specific gravity of the solids is 5.0 and the rfso is 400 pim. The calculated head on slurry is 35 m. Determine the head ratio and the equivalent water head on the pump performance curve. 

Figure 9.31 Schematic diagram showing pump performance and installation characteristic curves (a) fluid circulation at high differential pressure (low specific speed) (b) fluid circulation at high system pressure but low pressure differential (i.e. at a higher specific speed). Curve (a) is the installation characteristic curve the remaining curves are pump performance curves for a set...

Why Because I was running on the flat portion of the cooling-water supply pump performance curve. 

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 compressor is modeled with either the new RELAP5-3D compressor component or a pump component. The RELAP5-3D compressor component is used for all steady state and transient runs except for the complete loss of electrical load (overspeed) transient in which the pump component was used, The compressor component requires compressor data that covers the range of flow rates and shaft speeds that occur during a transient. Since the overspeed transient takes shaft speed well beyond the available compressor data, the necessary data extrapolation introduced too much error into the calculation and in many cases made the compressor unstable. The pump model, on the other hand, is able to calculate performance at the very high shaft speeds, and the pump performance curves were extrapolated to the necessary operating points. More compressor data would have been required to refine the analysis of the overspeed transient had the design continued. 

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