Know and Understand Centrifugal Pumps

270 Pages·2004·7.67 MB·English

Know and Understand
CUSTODIO
c

Know and
Understand
Cent ri fu ga I
Pumps

Know and
Understand
Centr if ug a I
Pumps
by Larry Bachus and
Angel Custodio
ELSEVIER
UK Elsevier Ltd, The Boulevard, Langford Lane, Cdlington, Oxford
OX5 lGB, UK
USA Elsevier Inc, 360 Park Avenue South, New York, NY 10010 - 1710 ,
USA
JAPAN Elsevier Japan, Tsunashima Building Annex, 3-20-1 2 Yushima,
Bunkyo-ku, Tokyo 113 , 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,
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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
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Typeset by Land & Unwin (Data Sciences) Ltd, Bugbrooke
Printed and bound in Great Britain by Biddles Ltd, Guildford and King’s Lynn
Contents
Prologue xi
...
About the Authors xlll
1 Basic Pump Principles 1
Introduction 1
How do pumps work? 1
Pressure measurement 4
Atmospheric pressure (ATM) 4
Absolute pressure (psia) 4
Gauge pressure (psig) 5
Vacuum 5
Pump head 5
Specific gravity 6
Pressure measurement 6
Pressures inside the pump 7
2 NPSH, Net Positive Suction Head 12
Introduction 12
Definition of NPSHr (required) 13
Definition NPSHa (available) 14
3 Cavitation 24
Introduction 24
Vapor pressure 24
Cavitation 25
The effects of vapor pressure on pump performance 25
Cavitation: A practical discussion 26
Review for preventing cavitation 35
Contents
Cavitation review 37
Do something about cavitation! 37
4 The Affinity Laws 39
Introduction 39
The Laws 39
The Affinity Laws and the impeller diameter 42
What’s the practical application of these laws? 42
5 Useful Work and Pump Efficiency 44
Useful work from a pump 44
Flow determination 46
Pump efficiency 48
Factors that affect the efficiency 48
Calculating pump efficiency 50
6 Pump Classification 51
Introduction 51
Positive displacement pumps 51
Centrifugal pumps 54
Conceptual difference 55
Centrifugal volute pumps 56
Types of centrifugal pumps 57
Overhung impeller 57
Impeller between the bearings 57
Turbine pumps 58
Specific duty pumps 58
The typical ANSI pump 58
API (American Petroleum Institute) pumps 59
Vertical turbine pumps 60
Non-metallic pumps 61
Magnetic drive pumps 62
Canned motor pumps 63
Pump impellers 64
Turbine impellers 65
Conventional impellers 66
Suction specific speed, Nss 66
Open impellers 70
Semi open impeller 71
Totally enclosed impeller 71
Wear bands 72
Specific speed, Ns 73
Contents
7 Understanding Pump Curves 76
Pump performance curves 76
History 77
Head versus pressure 77
H-Q 78
Pump efficiency 80
The energy (BHp) curve 81
The pump’s minimum requirements (NPSH) 82
Special design pumps 85
Family curves 85
8 The System Curve 92
The system controls the pump 92
The elements of the Total Dynamic Head (TDH) 92
Determining the Hs 96
Determining the Hp 96
Calculating the Hf and Hv 97
The dynamic system 110
Variable elevations 110
The happy zone 113
Dynamic pressures 113
Variable resistances 116
Short term resistance changes 116
Long term resistance changes 117
Pumps in parallel and pumps in series 120
Pumps in parallel 122
Three tips 123
Pumps running in series 124
Combined parallel and series pump operation 125
9 Shaft Deflection 128
Introduction 128
Operation, design and maintenance 133
Signs of shaft deflection 136
Interpreting the evidence 137
The sweet zone 140
The dual volute pump 141
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