Know and Understand CUSTODIO c Know and Understand Cen tr if ug a I Pumps Know and Understand Cent r if u g a I Pumps by Larry Bachus and Angel Custodio ELSEVIER UK USA JAPAN Elsevier Ltd, The Boulevard, Langford Lane, Cdlington, Oxford OX5 lGB, UK Elsevier Inc, 360 Park Avenue South, New York, NY 1001 0- 171 0, USA Elsevier Japan, Tsunashima Building Annex, 3-20- 12 Yushima, Bunkyo-ku, Tokyo 11 3, Japan Copyright 0 2003 Bachus Company, Inc. Published by Elsevier Ltd All rights reserved. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means: electronic, electrostatic, magnetic tape, mechanical, photocopying, recording or otherwise, without permission in writing from the publishers. British Library Cataloguing in Publication Data Bachus, Larry Know and understand centrifugal pumps 1 .Centrifugal pumps I.Title II.Custodio, Angel 62 1.6’7 ISBN 1856174093 No responsibility is assumed by the Publisher for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions or ideas contained in the material herein. Published by Elsevier Advanced Technology, The Boulevard, Langford Lane, Kidlington, Oxford OX5 lGB, UK Tel: +44(0) 1865 843000 Fax: +44(0) 1865 843971 Typeset by Land & Unwin (Data Sciences) Ltd, Bugbrooke Printed and bound in Great Britain by Biddles Ltd, Guildford and King’s Lynn Contents Prologue About the Authors 1 Basic Pump Principles Introduction How do pumps work? Pressure measurement Atmospheric pressure (ATM) Absolute pressure (psia) Gauge pressure (psig) Vacuum Pump head Specific gravity Pressure measurement Pressures inside the pump 2 NPSH, Net Positive Suction Head Introduction Definition of NPSHr (required) Definition NPSHa (available) 3 Cavitation Introduction Vapor pressure Cavitation The effects of vapor pressure on pump performance Cavitation: A practical discussion Review for preventing cavitation xi xlll 1 1 1 4 4 4 5 5 5 6 6 7 12 12 13 14 24 24 24 25 25 26 35 Contents Cavitation review Do something about cavitation! 4 The Affinity Laws Introduction The Laws The Affinity Laws and the impeller diameter What’s the practical application of these laws? 5 Useful Work and Pump Efficiency Useful work from a pump Flow determination Pump efficiency Factors that affect the efficiency Calculating pump efficiency 6 Pump Classification Introduction Positive displacement pumps Centrifugal pumps Conceptual difference Centrifugal volute pumps Types of centrifugal pumps Overhung impeller Impeller between the bearings Turbine pumps Specific duty pumps The typical ANSI pump API (American Petroleum Institute) pumps Vertical turbine pumps Non-metallic pumps Magnetic drive pumps Canned motor pumps Pump impellers Turbine impellers Conventional impellers Suction specific speed, Nss Open impellers Semi open impeller Totally enclosed impeller Wear bands Specific speed, Ns 37 37 39 39 39 42 42 44 44 46 48 48 50 51 51 51 54 55 56 57 57 57 58 58 58 59 60 61 62 63 64 65 66 66 70 71 71 72 73 Contents 7 Understanding Pump Curves Pump performance curves History Head versus pressure H-Q Pump efficiency The energy (BHp) curve The pump’s minimum requirements (NPSH) Special design pumps Family curves 8 The System Curve The system controls the pump The elements of the Total Dynamic Head (TDH) Determining the Hs Determining the Hp Calculating the Hf and Hv The dynamic system Variable elevations The happy zone Dynamic pressures Variable resistances Short term resistance changes Long term resistance changes Pumps in parallel and pumps in series Pumps in parallel Three tips Pumps running in series Combined parallel and series pump operation 9 Shaft Deflection Introduction Operation, design and maintenance Signs of shaft deflection Interpreting the evidence The sweet zone The dual volute pump 76 76 77 77 78 80 81 82 85 85 92 92 92 96 96 97 110 110 113 113 116 116 117 120 122 123 124 125 128 128 133 136 137 140 141 vi i [...]... explained by math Cartridge mechanical seals Double seals The tandem dual seal The back-to-back double seal 18 0 18 0 18 2 18 4 18 5 18 6 18 6 18 7 18 7 18 8 18 9 19 0 19 2 19 4 19 5 19 6 n Vlll 15 5 15 7 15 9 16 3 16 7 Contents 19 7 19 8 19 8 19 9 200 The face-to-face dual seal Support systems for dual seals The thermal convection tank The turbo tank The pumping unit 14 Failure Analysis of Mechanical Seals Causes of premature... Packing History Vegetable fibers Reciprocating action Packing Rotary action Synthetic fibers Compression packing The lantern ring The packing lubricant Stages in the life of packing 17 1 17 1 17 1 17 2 17 3 17 3 17 4 17 5 17 7 17 8 17 8 13 Mechanical Seals Pump packing History The mechanical seal The single, unbalanced, inside mounted mechanical seal The single, outside-mounted, unbalanced seal The single, balanced,...Contents 10 Pump and Motor Alignment Introduction Types of misalignment Alignment techniques Equipment alignment sequence Coupling alignment 14 2 14 2 14 4 14 5 15 3 15 3 11 Bearings Introduction Bearing lubrication Bearing failure Bearing maintenance Bearing seals 15 5 12 Pump Shaft Packing History Vegetable fibers Reciprocating action Packing... springs clog and jam The shaft frets under the shaft seal Incorrect installation dimension Environmental controls for difficult sealing applications Difficult pumping applications for mechanical seals Environmental controls Proper pump repair alignment methods 202 202 204 209 210 21 1 212 213 2 14 215 222 15 Common Sense Failure Analysis Pump maintenance files Failure analysis on centrifugal pumps Why... hands-on maintenance and operator inspections Angel conducts seminars o n pumps, I mechanical components, computerized inventory control and maintenance management He is also a member of ASME, and the Puerto Rican College of Engineers Know and Understand Centrifugal Pumps / I \\ r suction piping The fluid must be available to the pump with sufficient energy so that the pump can work with the fluid’s... sufficient energy Centrifugal pumps cannot suck or draw the liquid into the pump housing The principal pumping unit of a centrifugal pump is the volute and impeller (See Figure 1- 3) The impeller is attached to a shaft The shaft spins and is powered by the motor or driver We use the term driver because some pumps are attached to pulleys or transmissions The fluid enters into the eye of the impeller and is trapped... is this pump in the shop? 226 226 227 228 16 Avoiding Wear in Centrifugal Pumps Introduction Erosion Corrosion Wear rings Fluid velocity accelerates wear Turbulence Throttling 232 232 232 233 233 235 235 236 17 Pump Piping Introduction Piping design to drain tanks and sumps The Submergence Laws 238 238 238 243 248 Index ix Prologue productive pump operation and contain maintenance costs This book will... repairing industrial pumps About the Authors Angel Custodio I c Angel specializes in the installation and implementation of Preventive Maintenance Systems through his consulting engineering company formed in 19 87 in Puerto Rico His installations have given him the opportunity to look into different approaches to hands-on maintenance and operator inspections Angel conducts seminars o n pumps, I mechanical... thickness of the casing and the tolerances, and the strength of the pump components As the pump performs its duty over time, and fluid passes through the pump, erosion and abrasive action will cause the close tolerance parts to wear These parts may be piston rings, reciprocating rod seals, a flexing diaphragm, or meshed gear teeth As these parts wear, the pump will lose its efficiency and ability to pump... changed with a degree of frequency based on time and the abrasive and lubricating nature of the fluid Changing these parts should not be Basic Pump Principles ROTATION Fiaure 1- 3 viewed as breakdown maintenance Nothing is broken This periodic servicing is actually a production function to return the pump to its best or original efficiency Centrifugal pumps also require that the fluid be available to . tandem dual seal The back-to-back double seal 14 2 14 2 14 4 14 5 15 3 15 3 15 5 15 5 15 7 15 9 16 3 16 7 17 1 17 1 17 1 17 2 17 3 17 3 17 4 17 5 17 7 17 8 17 8 18 0 18 0 18 2 18 4 18 5 18 6. 77 77 78 80 81 82 85 85 92 92 92 96 96 97 11 0 11 0 11 3 11 3 11 6 11 6 11 7 12 0 12 2 12 3 12 4 12 5 12 8 12 8 13 3 13 6 13 7 14 0 14 1 vi i Contents 10 Pump and Motor Alignment. Know and Understand CUSTODIO c Know and Understand Cen tr if ug a I Pumps Know and Understand Cent r if u g a I Pumps by Larry Bachus and Angel Custodio