Centrifugal Pump User's Guidebook PROBLEMS AND SOLUTIONS

Transcription

1 Centrifugal Pump User's Guidebook PROBLEMS AND SOLUTIONS

2 Centrifugal Pump User's Guidebook PROBLEMS AND SOLUTIONS SAM YEDIDIAH CHAPMAN & HALL loop An International Thomson Publishing Company New York' Albany Bonn' Boston' Cincinnati Detroit Madrid' Melbourne Mexico City Pacific Grove Paris San Francisco Singapore Tokyo Toronto Washington

3 Cover design: Robert Freese Copyright 1996 by Chapman & Hall Softcover reprint of the hardcover I st edition 1996 Chapman & Hall 115 Fifth Avenue New York. NY Thomas Nelson Australia 102 Dodds Street South Melbourne Victoria. Australia Nelson Canada 1120 Birchmount Road Scarborough. Ontario Canada M1K 5G4 International Thomson Editores Campos EIiseos 385. Piso 7 Col. Polanco Mexico O.F. Mexico Chapman & Hall 2-6 Boundary Row London SE 1 8HN England Chapman & Hall GmbH Postfach Weinheim Germany International Thomson Publishing Asia 221 Henderson Road #05-10 Henderson BuUding Singapore 0315 International Thomson Publishing-Japan Hirakawacho-cho Kyowa BuUding. 3F Hirakawacho-cho Chiyoda-ku. 102 Tokyo Japan All rights reserved. No part of this book covered by the copyright hereon may be reproduced or used in any form or by any means-graphic. electronic. or mechanical. including photocopying. recording. taping. or information storage and retrieval systems-w1thout the written permission of the publisher XXX Libnuy of Congreu CatalogiDg-in-PubUcatiOD Data Yedidiah. S. Centrifugal Pump User's Guidebook: problems and solutions / Shmariahu Yedidiah. p. cm. Includes bibliographical references and index:. ISBN-13: : / e-isbn-13: Centrifugal Pumps-Handbooks. manuals. etc. I. Title. TJ919.Y '7--dc CIP Visit Chapman & Hall on the Internet: To order this or any other Chapman & Hall book. please contact Internatlooal ThOmsoD PubUshiDg, 7625 Empire Drive. Florence. KY Phone: (606) or Fax: (606) order@chaphall.com. Fbr a complete listing of Chapman & Hall titles. send your request to Cbapman II: Hall, Dept. BC, 115 Fifth Avenue, New York, NY

4 Contents Preface vii PART I. INTRODUCTION 1 Chapter 1. Rotodynamic Pumps 3 Chapter 2. Performance Chracteristics of Centrifugal Pumps 13 Chapter 3. Classification of Centrifugal Pumps 19 PART II. PERFORMANCE FACTORS 29 Chapter 4. Chapter 5. Chapter 6. Chapter 7. Chapter 8. Chapter 9. Chapter 10. Chapter 11. Effects of Free Air in the Pumped Liquid 31 Cavitation 33 Cavitation in Centrifugal Pumps 45 Losses of Energy 61 Effects of Temperature and Viscosity on Pump Performance 75 Recirculation 79 Axial and Radial Thrust and Balancing 97 Miscellaneous Factors that Affect Pump Performance III PART III. Chapter 12. Chapter 13. Chapter 14. Chapter 15. Chapter 16. Chapter 17. Chapter 18. Chapter 19. Chapter 20. PROBLEMS ENCOUNTERED WITH CENTRIFUGAL PUMPS Testing Pump Performance at Reduced NPSH Pumping System Layout Installation. Handling, and Operation of Pumps and Pumping Systems Problems with Bearings Sealing Rotating Parts Miscellaneous Studies Problems Related to Specific Circumstances Special Cases that Have Proven Very Difficult to Solve v

5 VI Contents PART IV. SOLVING PUMP PROBLEMS 271 Chapter 21. Chapter 22. Chapter 23. Solving Problems Prior to Visiting the Site Conclusions Drawn from Visual Inspection of Failed Parts On-Site Inspection and Testing PART V. ELIMINATING PUMP PROBLEMS AND MODIFYING PERFORMANCE 297 Chapter 24. Chapter 25. Chapter 26. Chapter 27. Chapter 28. Remedial Methods The Effects of Speed and Impeller OD on Pump Performance The Effects of Reducing the Impeller Width Moditying the Casing Geometry Various Methods of Altering Pump Performance PART VI. Chapter 29. Chapter 30. A GLIMPSE OF THE FUTURE New Findings Concerning the Mode of Operation of Rotodynamic Impellers Some Future Applications of the Presented Theory Appendix A. Checklist of Problems with Centrifugal Pumps and their Causes 1. Pump Does Not Develop Any Head, Nor Does It Deliver Liquid 2. Pump Develops Some Pressure, but Delivers No Liquid 3. Pump Delivers Less Liquid Than Expected 4. Pump Does Not Develop Enough Pressure 5. Shape of Head-Capacity Curve Differs from Rated Curve 6. Pump Consumes Too Much Power 7. Pump Does Not Perform Satisfactorily, Although Nothing Appears to be Wrong with Pumping Unit or System 8. Pump Operates Satisfactorily During Start, but Performance Deteriorates in a Relatively Short Time 9. Pump is Operating with Noise, Vibrations, or Both 10. Stuffing Box Leaks Excessively 11. Packing Has Short Life 12. Mechanical Seal Has Short Life 13. Mechanical Seal Leaks Excessively 14. Bearings Have Short Life

6 Contents Vll 15. Bearings Overheat 16. Bearings Operate with Noise 17. Pump Overheats, Seizes, or Both 18. Impeller or Casing, or Both, Has Short Life 19. Loud Blow is Heard Each Time Pump is Started or Stopped 20. Casing Bursts Each Time Pump is Started or Stopped 21. Gaskets Leak During Pump Operation 22. Flow-Rate Periodically Decreases, or Stops Completely, then Returns to Normal 23. Pump Develops Cavitation when the Available NPSH is Increased Appendix B. Tables Vapor Pressures of Water at Different Temperatures Gall Resistance of Material Combinations Packing Selections Tables of Chemical Compatibility of Materials Bibliography 375 Index 379

7 Preface This book discusses two classes of activities: preventive procedures and corrective steps. Sometimes these two activities are so intimately connected that it is impossible to separate one from the other. Also, to execute these activities properly, an in-depth knowledge and understanding of centrifugal pump operation and diagnostic procedures is required. The pump designer must adopt preventive steps to keep the possibility of failure at a minimum. A pump must be selected carefully for each application and the system of which it is destined to be a part must also be designed carefully. Preventive damage control also requires great care in the manufacture, installation, and maintenance of a pump. The corrective procedures are related to diagnosing the cause of the malfunction and taking the proper steps to correct the problem. Implementing corrective and preventive procedures requires an in-depth knowledge of what makes a pump operate satisfactorily and what affects its operation. It also requires a wide knowledge of how different factors can affect the performance of a given pump. The objective of this book is to provide the reader with the information required to prevent, diagnose, and solve the widest possible spectrum of problems encountered with centrifugal pumps. Because of the wide range of problems dealt with in this book, it may prove to be of great assistance to a very diverse group. It is intended to: 1. Explain to pumping system designers how the layout of the suction fump, the suction line, and the discharge line can affect pump performance. 2. Identify problems pump designers must take into account in order to incorporate proper preventive and safety features that will make their designs more competitive. 3. Describe the characteristics of materials and workmanship that are crucial for turning out a good product. This will help quality-control and production personnel establish and maintain the delicate balance between cost and quality. 4. Help those concerned with the selection and purchase of pumps make the best choice. 5. Make it easier for maintenance personnel to determine and locate the source of any problem and provide guidelines for handling these problems. The book also outlines steps that may be taken when a pump has to operate under unanticipated conditions. ix

8 x Preface 6. Caution personnel responsible for installing pumps and the pumping system about problems they may create by not following correct installation procedures. 7. Provide pump attendants with a better understanding of how the equipment functions and how to identify signs of developing malfunctions. This book may be of interest and assistance to people with different levels of education and training. We therefore start with a review of some of the most basic principles on which centrifugal pump operation is founded. This has been done for the purpose of making this book accessible to those who may not be familiar with these principles. People who are familiar with the problems discussed in the introductory part of this book may safely skip it and start directly with the more advanced topics. Troubleshooting is, to a great extent, the ability to deal with unforeseen events. This book tries to deal with as many situations as possible. Most problems can be solved simply by consulting the checklists and following the instructions without worrying about the analytical background. On the other hand, unique problems are always possible. These cases are often very difficult to analyze and solve. In such cases, an in-depth understanding of the most basic principles can be of great help in finding the proper solution. Sam Yedidiah

9 Centrifugal Pump User's Guidebook PROBLEMS AND SOLUTIONS