Selecting a Centrifugal Pump by System Analysis

Randall W. Whitesides, P.E.

Course Outline

Pump selection should be based on system evaluation, not on maximum flow and head. Maximum capacity and head are important pieces of information, but much more must be known to achieve the best pump installation. Just because a pump delivers enough liquid at the desired pressure does not prove the pump is adequate. The information presented in this course provides much of the information needed for an evaluation of most types of systems. Additional data will be needed for specific installations.

This course includes a multiple choice quiz at the end, which is designed to enhance the understanding of the course materials.

Learning Objective

At the conclusion of this four-hour course, the student will learn the

• Basic forms of pump impeller characteristic curves;
• Methods and their appropriateness to mathematically represent the curves;
• Methods to develop a system curve and accurately mathematically define it;
• Means to analytically determine the operation point (performance) of a given pump in a defined system; and
• Method to comprehensively select and size the most efficient pump based on the above information.
  

Intended Audience

This course is intended primarily for Chemical and Mechanical Engineers in the process industries. Civil, Environmental, and Petroleum Engineers whose endeavors involve centrifugal pumps will have equal interest. It is assumed that the student has a rudimentary knowledge of fluid static and dynamic concepts.

Benefits for Attendees

This course will review the various aspects of centrifugal pump operational head and capacity, and the piping circuit resistance components of independent and dependent system heads. Examples of pumping systems, complete with hydraulic analytical solutions, are provided to aid in the understanding of the presented material. Additional and interesting hydraulic facts are randomly interspersed throughout the course.

Course Content

The course content is in a PDF file (331 KB) Selecting a Centrifugal Pump by System Analysis.

Course Summary

In the beginning of the course a selection and sizing method was outlined that made the case of the steady-state assumption in a transient process. As is true with many topics, there are simple, but unfortunately, incorrect methods of performing analysis. The correct method to size a centrifugal pump is presented in the following step by step procedure:

1. Using the normal or average flow and head requirement of the process or system obtained from a careful and considered process study, make a tentative size selection from a pump manufacturer's graphical coverage chart (or map) of all available sizes.



2. Superimpose the system curve, preferably mathematically, or alternatively graphically, on the performance curve of the tentatively selected pump from Step 1.



3. Select the impeller size and speed to match the intersection of the system curve. Generate additional system curves that represent minimum and maximum flows and/or changes in static fluid levels so that the performance of the impeller size selected for normal conditions can be evaluated over the entire anticipated operating range.



4. Check to insure that ample margin exists between Net Positive Suction Head Available and Net Positive Suction Head Required at the various operating points.



5. Estimate the pump's efficiency at the operation point determined in Step 3 and calculate the power requirements.



6. Repeat the above procedure for larger and smaller pumps in the vicinity of the tentative pump selection to compare efficiency at the normal operation point.



7. Make the final selection based on a life-cycle cost analysis comparison of each pump considered in Step 6 that efficiently satisfies the process requirements.

Step 2 is critical in the pump selection process above.

 

Additional Resources

The following texts offer excellent additional information on pumps and hydraulic systems. These books can be reviewed to supplement the material that is supplied in this course:

1. Flow of Fluids through valves, fittings, and pipe, Technical Paper No. 410, Crane Company, latest edition.
2. Cameron Hydraulic Data, Ingersoll-Dresser Pump Co. (now Flowserve), latest edition.
3. Standards for Centrifugal, Rotary and Reciprocating Pumps, Hydraulic Institute, latest edition.
4. API 610 Centrifugal Pumps for Petroleum, Heavy Duty Chemical and Gas Industry Services, latest edition.

Once you finish studying the above course content, you need to take a quiz to obtain the PDH credits.

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DISCLAIMER: The materials contained in the online course are not intended as a representation or warranty on the part of PDHonline.com or any other person/organization named herein. The materials are for general information only. They are not a substitute for competent professional advice. Application of this information to a specific project should be reviewed by a registered professional engineer. Anyone making use of the information set forth herein does so at their own risk and assumes any and all resulting liability arising therefrom.

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