HI 1.3 for Design and Application.pdf

American National Standard for

Centrifugal Pumps for Design and Application

Sponsor Hydraulic Institute

Approved November 9,1999 American National Standards Institute, Inc.

American Approval of an American National Standard requires verification by ANSl that the requirements for due process, consensus and other criteria for approval have been met National by the standards developer.

Standard Consensus is established when, in the judgement of the ANSl Board of Standards Review, substantial agreement has been reached by directly and materially affected interests. Substantial agreement means much more than a simple majority, but not necessarily unanimity. Consensus requires that all views and objections be considered, and that a concerted effort be made toward their resolution.

The use of American National Standards is completely voluntary; their existence does not in any respect preclude anyone, whether he has approved the standards or not, from manufacturing, marketing, purchasing, or using products, processes, or procedures not conforming to the standards.

The American National Standards lnstitute does not develop standards and will in no circumstances give an interpretation of any American National Standard. Moreover, no person shall have the right or authority to issue an interpretation of an American National Standard in the name of the American National Standards Institute. Requests for interpretations should be addressed to the secretariat or sponsor whose name appears on the title page of this standard.

CAUTION NOTICE: This American National Standard may be revised or withdrawn at any time. The procedures of the American National Standards Institute require that action be taken periodically to reaffirm, revise, or withdraw this standard. Purchasers of American National Standards may receive current information on all standards by call- ing or writing the American National Standards Institute.

Published By

Hydraulic lnst i tute 9 Sylvan Way, Parsippany, NJ 07054-3802 www.purnps.org

Copyright O 2000 Hydraulic lnstitute All rights resewed.

No part of this publication may be reproduced in any form, in an electronic retrieval system or otherwise, without prior written permission of the publisher.

Printed in the United States of America

ISBN 1-880952-28-9

Contents Page

Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii 1.3 Design and application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.3.1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

. . . . . . . . . . . . . . . . . . . . . . . . . 1.3.2 Preferred units for pump applications 1 1.3.3 Typical applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.3.3.1 Booster sewice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.3.3.2 Process sewice (chemical, petrochemical, injection) . . . . . . . . . . . . . 1

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3.3.3 Transfer pumping 4 1.3.3.4 Mine dewatering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3.3.5 Well pumping 4 1.3.3.6 Irrigation sewice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3.3.7 Pumps for steam power plants 4 1.3.3.8 Fire pumps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 1.3.3.9 Pumps used as hydraulic turbines . . . . . . . . . . . . . . . . . . . . . . . . . . 11 1.3.3.1 0 General purpose sewice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 1.3.3.1 1 Wastewater service (solids and non-clog) . . . . . . . . . . . . . . . . . . . . . 14 1.3.3.12 Pulp and paper applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 1.3.3.1 3 Slurty sewice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 1.3.3.1 4 Liquids with vapor or gas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 1.3.4 Performance, selection criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 1.3.4.1 System requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 1.3.4.2 Determination of operating duty . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

. . . . . . . . . . . . . 1.3.4.3 Efficiency prediction method for centrifugal pumps 49 . . . . . . . . . . . . . . . . . 1.3.4.4 Operation away from the best efficiency point 56

1.3.4.5 Noise levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3.4.6 Suction conditions 57

1.3.4.7 Mechanical features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 1.3.4.8 Impeller types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 1.3.4.9 Casing type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 1.3.4.1 0 Drivers: type and size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76

. . . . . . . . . . . 1.3.4.1 1 Pump liquid temperature limits on end suction pumps 78 1.3.5 Horizontal pump baseplate design . . . . . . . . . . . . . . . . . . . . . . . . . . 78 1.3.5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78 1.3.5.2 Functional requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 1.3.5.3 Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 1.3.5.4 Tolerancing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80 1.3.5.5 Shims and fasteners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 1.3.5.6 Stress levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81

1.3.5.7 Rigidity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 1.3.5.8 Miscellaneous criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84

.Appendix A Torsional Stiffness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86

Appendix B Recommended Equipment Mounting Drilling Dimensions . . . . . . 87

Appendix C References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88

AppendixD Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89

Figures 1.47 -- Diagram of a simple steam power cycle . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.48 -- Diagram of a typical condensing steam power plant . . . . . . . . . . . . . . . . 5 1.49 - Diagram of a closed feedwater cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 1.50 - Diagram of an open feedwater cycle with one deaerator and three closed heaters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 1.51 - Turbine characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 1.52-Turbineperformance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 1.53 - Self-priming pump -construction industry . . . . . . . . . . . . . . . . . . . . . . 14 1.54 - Self-priming pump - chemical industry . . . . . . . . . . . . . . . . . . . . . . . . 15 1.55 - Nomograph of the relationship of concentration to specific gravity in aqueous slurries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 1.56 -Typical performance characteristics - non-settling slurries . . . . . . . . . 19 1.57 -Typical performance characteristics -settling slurries . . . . . . . . . . . . 19 1.58 - Effect of gas on pump performance . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 1.59-Inducer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 1.60-Venting the eye of the impeller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 1.61 -Top suction impeller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 1.62 - Pump versus system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 1.63-Torquecurve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 1.64A - Performance correction chart for viscous liquids (metric) . . . . . . . . . . 24 1.64B - Performance correction chart for viscous liquids (US units) . . . . . . . . 25 1.65A - Performance correction chart for viscous liquids (metric) . . . . . . . . . . 26 1.658 - Performance correction chart for viscous liquids (US units) . . . . . . . . 27 1.66A - Sample performance chart (Metric) . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 1.66B - Sample performance chart (US Units) . . . . . . . . . . . . . . . . . . . . . . . . 31 1.67A - Recommended typical operating speed limits for single suction pumps (metric) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 1.678 - Recommended typical operating speed limits for single suction pumps (US units) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 1.68A - Recommended typical operating speed limits for double suction pumps (metric) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

1.686 . Recommended typical operating speed limits for double suction pumps (US units) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 1.69A - NPSHR reduction for pumps handling hydrocarbon liquids and high-temperature water (metric) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 1.696 - NPSHR reduction for pumps handling hydrocarbon

. . . . . . . . . . . . . . . . . . . . . . . . . . liquids and high-temperature water (US units) 41 1.70 - Pumps operating in series . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 1.71 - Pumps operating in parallel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.72A - Pump performance (Metric) 44 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.73A - Temperature rise (Metric) 44

1.726 -Pump performance (US Units) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 1.736 -Temperature rise (US Units) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 1.74 - Impeller with angled outside diameter . . . . . . . . . . . . . . . . . . . . . . . . . . 49 1.75A - Optimum generally attainable efficiency chart (Metric) . . . . . . . . . . . . 50 1.756 -Specific speed-efficiency correction chart (Metric) . . . . . . . . . . . . . . . 50 1.75C - Optimum generally attainable efficiency chart (US Units) . . . . . . . . . . 51

. . . . . . . . . . . . . 1.75D - Specific speed-efficiency conection chart (US Units) 51 1.76A - Deviation from generally attainable efficiency (Metric) . . . . . . . . . . . . 52 1.766 -Deviation from generally attainable efficiency (US Units) . . . . . . . . . . 52 1.77A - Estimated efficiency increase due to improved surface finish (Metric) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 1.776 - Estimated efficiency increase due to improved surface finish (US Units) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 1.78A - Estimated efficiency decrease due to increased wear ring clearance (Metric) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 1.786 - Estimated efficiency decrease due to increased wear ring clearance (US Units) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 1.79-Inducer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 1 . 80 - Single volute casing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 1.81 - K versus rate of flow for single volute casing . . . . . . . . . . . . . . . . . . . . 59 1 . 82 - Dual (double) volute casing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 1.83 - K versus rate of flow for dual (double) volute casing . . . . . . . . . . . . . . . 59 1 . 84 - Circular casing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60 1.85 - Pressure distribution on enclosed impeller shrouds . . . . . . . . . . . . . . . 60 1.86- Enclosed impeller with plain back shroud . . . . . . . . . . . . . . . . . . . . . . . 61 1 . 87 - Impeller with back ring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62 1.88 - Mechanical seal classifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 1.89 - Stuffing-box without lantern ring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 1.90- Stuffing-box with lantern ring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70 1.91 - Overhung impeller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71 1.92 - Impeller between bearings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.93 - Grouted baseplate 79

1.94 -- Free-standing baseplate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 1.95 -- Height of mounting surfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 1.96 - Equipment mounting surface flatness . . . . . . . . . . . . . . . . . . . . . . . . . . 81 1.97- Motor mounting pads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 1.98 - Mounting block dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 A.l - Baseplate support and anchoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86 B.l - Recommended equipment mounting drilling dimensions . . . . . . . . . . . . 87

Tables

1.3.2 -Subscripts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.3.3A - Sample calculations (Metric) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 1.3.3B - Sample calculations (US Units) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 1.3.4 -The influence of pump type on efficiency . . . . . . . . . . . . . . . . . . . . . . . 56 1.3.5 -Rolling element bearing types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 1.3.6 - Product lubricated sleeve bearing material selection guide (commonly used in vertical turbine pumps) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66 1.3.7 -Guidelines for minimum and maximum pump liquid temperature for cast grey iron and ductile iron pumps ("C) . . . . . . . . . . . . . . . . 78 1.3.8 - Guidelines for minimum and maximum pump liquid temperature for cast grey iron and ductile iron pumps ( O F ) . . . . . . . . . . . . . . . . 78 1.3.9 - Metric manufacturing tolerances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80 1.3.10 - US units manufacturing tolerances . . . . . . . . . . . . . . . . . . . . . . . . . . . 80

Foreword (Not part of Standard)

Purpose and aims of the Hydraulic lnstitute The purpose and aims of the lnstitute are to promote the continued growth and well-being of pump manufacturers and further the interests of the public in such matters as are involved in manufacturing, engineering, distribution, safety, transportation and other problems of the industry, and to this end, among other things: a) To develop and publish standards for pumps; b) To collect and disseminate information of value to its members and to the

public; c) To appear for its members before governmental departments and agencies

and other bodies in regard to matters affecting the industry; d) To increase the amount and to improve the quality of pump service to the public; e) To support educational and research activities; f) To promote the business interests of its members but not to engage in busi-

ness of the kind ordinarily carried on for profit or to perform particular services for its members or individual persons as distinguished from activities to improve the business conditions and lawful interests of all of its members.

Purpose of Standards 1) Hydraulic lnstitute Standards are adopted in the public interest and are

designed to help eliminate misunderstandings between the manufacturer, the purchaser and/or the user and to assist the purchaser in selecting and obtaining the proper product for a particular need.

2) Use of Hydraulic lnstitute Standards is completely voluntary. Existence of Hydraulic lnstitute Standards does not in any respect preclude a member from manufacturing or selling products not conforming to the Standards.

Definition of a Standard of the Hydraulic lnstitute Quoting from Article XV, Standards, of the By-Laws of the lnstitute, Section B: "An lnstitute Standard defines the product, material, process or procedure with reference to one or more of the following: nomenclature, composition, construction, dimensions, tolerances, safety, operating characteristics, performance, quality, rating, testing and service for which designed."

Comments from users Comments from users of this Standard will be appreciated, to help the Hydraulic lnstitute prepare even more useful future editions. Questions arising from the content of this Standard may be directed to the Hydraulic Institute. It will direct all such questions to the appropriate technical committee for provision of a suitable answer.

If a dispute arises regarding contents of an lnstitute publication or an answer provided by the lnstitute to a question such as indicated above, the point in question shall be referred to the Executive Committee of the Hydraulic Institute, which then shall act as a Board of Appeals.

Revisions The Standards of the Hydraulic Institute are subject to constant review, and revisions are undertaken whenever it is found necessary because of new developments and progress in the art. If no revisions are made for five years, the standards are reaffirmed using the ANSI canvass procedure.

Units of Measurement Metric units of measurement are used; and corresponding US units appear in brackets. Charts, graphs and sample calculations are also shown in both metric and US units. Since values given in metric units are not exact equivalents to values given in US units, it is important that the selected units of measure to be applied be stated in reference to this standard. If no such statement is provided, metric units shall govern.

Consensus for this standard was achieved by use of the Canvass Method The following organizations, recognized as having an interest in the standardiza- tion of centrifugal pumps were contacted prior to the approval of this revision of the standard. Inclusion in this list does not necessarily imply that the organization concurred with the submittal of the proposed standard to ANSI.

A.R. Wilfley & Sons ANSIMAG lnc. Bechtel Corp. Black & Veatch Brown & Caldwell Camp Dresser 8 McKee, Inc. Carver Pump Company Cheng Fluid Systems, Inc. Crane Company, Chempump Div. Cuma S.A. Dean Pump Div., Metpro Corp. DeWante 8 Stowell Dow Chemical EnviroTech Pumpsystems Essco Pump Division Exeter Energy Ltd. Partnership Fairbanks Morse Pump Corp. Fluid Sealing Association Franklin Electric GKO Engineering Grundfos Pumps Corp. Illinois Dept. of Transportation IMC - Agrico Chemical Corp. Ingersoll-Dresser Pump Company IlT Fluid Handling (B & G) IlT Fluid Technology ITT Industrial Pump Group lwaki Walchem Corp. J.P. Messina Pump & Hydr. Cons. John Crane, Inc. Krebs Consulting Service

KSB, Inc. M.W. Kellogg Company Malcolm Pirnie, Inc. Marine Machinery Association Marley Pump Company Marshall Engineered Products

Company Montana State University MWI, Moving Water Industries Oxy Chem Pacer Pumps Paco Pumps, Inc. Pinellas Cty, Gen. Serv. Dept. The Process Group, LLC Raytheon Engineers & Constructors Reddy-Buffaloes Pump, Inc. Robert Bein, Wm. Frost & Assoc. Scott Process Equipment Corp. Settler Supply Company Skidmore South Florida Water Mgmt. Dist. Sta-Rite Industries, Inc. Sterling Fluid Systems (USA), lnc. Stone 8 Webster Engineering Corp. Sulzer Bingham Pumps, Inc. Summers Engineering, Inc. Systecon, Inc. Val-Matic Valve & Mfg. Corp. Yeomans Chicago Corp. Zoeller Engineered Products

HI Centrifugal Pump Design and Application - 2000

1.3 Design and application

The purpose of this section is to provide a guide for the application of centrifugal pumps for various services. No attempt has been made to cover all phases of centrifugal pump application, but an endeavor has been made to point out some of the principal features of pumps and the precautions which should be taken in their use.

1.3.1 Scope

This Standard is for centrifugal and regenerative turbine pumps of all industrial/commerciaI types except vertical single and multistage diffuser types. It includes design and application.

1.3.2 Preferred units for pump applications

Preferred terms, units and symbols to be used in the technology of pump applications are shown in Tables 1.3.1 and 1.3.2.

1.3.3 Typical applications

1.3.3.1 Booster service

Centrifugal pumps in this service handle liquids piped to them at various levels of pressure, normally above atmospheric, and discharge at a higher pressure into the system. Accurate specifications of the liquid characteristics and the range of suction pressures expected must be provided with rate of flow and total head for the pump manufacturer to make a proper selection.

1.3.3.2 Process service (chemical, petrochemical, injection)

1.3.3.2.1 Chemical pump

Pumps used for handling corrosive liquids or slurries are commonly termed chemical pumps. The materials of construction for the parts in contact with the liquid, including stuffing-boxes or seals, must be selected to offer maximum resistance to corrosion and abrasion at the pumping temperature, with due consideration to the economy of such use.

Each application must be carefully scrutinized to determine the severity of corrosion or abrasion, vis- cosities at the extreme pumping temperatures, the hazard involved in the material to be pumped, changes in the composition of the liquid, true vapor pressure,

net positive suction head (NPSH), prolonged operation at or near shut-off, or any other pertinent characteristics of the liquid or the application.

The physical and chemical properties of materials, the available forms, and methods of fabrication must be considered in the design of satisfactory equipment. Dissimilar materials in contact with the liquid pumped should be avoided unless the combination is one which is known to be satisfactory for the particular service.

Special seals or deep stuffing-boxes, with provision for lubrication or sealing by clear cold water, are frequently necessary. Large unobstructed liquid pas- sages are desirable. The unit should be designed for easy and quick disassembly for inspection, cleaning or repair. Water jackets, steam jackets, or smothering type glands may be mandatory. The need for these features can be determined only afler careful consideration of application requirements.

ANSIIASME B73.1, B73.2 and B73.5 covering specifications for horizontal end suction and vertical in-line pumps for chemical process may be used for more information.

The manufacturer's instructions with reference to installation should be strictly followed. In many cases, such instructions may be radically different from those for clear water pumps.

Regularly established schedules for periodic examina- tion and maintenance are essential.

1.3.3.2.2 Hot oil pump

Pumps for handling oils within the range of 150C to 450C (300F to 850F) are commonly termed hot oil pumps.

It is important that sufficient NPSH be available, as the liquid is almost always near the boiling point.

Provision should be made to allow self-venting of vapors from the impeller eye by venting the suction eye of the first stage except where the suction nozzle is in a vertical upward position.

The stuffing-boxes and bearing housings should be provided with cooling jackets. The glands should be of the smothering type. If packing conditions require seal oil, lantern rings together with the necessary pipe connections should be provided. During operation, the

Table 1.3.1 -Symbols

Symbol A

P (beta) D

A (delta) rl (eta) 9

Y (gamma) h H K I n

NPSHA NPSHR

NS v (nu) Z

P P '4 Q

RM RT

P (rho) S

S t

7 (tau) U v

+ (phi) X z

Term Area

Meter or orifice ratio Diameter Difference Efficiency

Gravitational acceleration Specific weight

Head Total head

Radial thrust factor Static lift Speed

Net positive suction head available Net positive suction head required Specific speed NS = ~ Q ' ~ I H ~ ' ~

Kinematic viscosity pi = 3.1416 Pressure

Power Rate of flow (Capacity) Rate of flow (Capacity)

Linear model ratio Radial thrust

Density Suction specific speed

= ~ Q ' ~ ~ / N P S H R ~ ~ ~ Specific gravity Temperature

Torque Residual unbalance

Velocity Velocity in vibration

Exponent Elevation gauge distance above

or halow datum

Metric unit square millimeter

dimensionless millimeter

dimensionless percent

meterlsecond squared

meter meter

dimensionless meter

revolutiondminute meter meter

not usedb millimeter squaredlsec

dimensionless kilopascal kilowatt

cubic meterlhour cubic meterlhour dimensionless

Newton kilogramlcubic meter

not usedb

dimensionless degrees Celsius Newton-meter

gram-centimeter meterlsecond

millimeterslsecond none meter

Abbreviation mm2 -

mm -

Yo m/s2

m m -

m

rpm m m -

mm2/s -

kPa kW

m3ih m3ih -

N kglm3 -

-

"C N.m

g-cm mls

mmls none

m

US Customary Unit sauare inches dimensionless

inches dimensionless

percent feetlsecond squared

poundslcubic foot feet feet

dimensionless feet

revolutionslminute feet feet

not usedb feet squaredlsecond

dimensionless pounddsquare inch

horsepower cubic feetlsecond US gallonslminute

dimensionless pounds (force)

pound masslcubic foot not used

dimensionless degrees Fahrenheit

pound-feet ounce-inches feeffsecond

incheslsecond none feet

Abbreviation in2 -

in -

Yo it/sec2 lb/It3

ft ft -

n rpm ft ft -

ft2lsec -

psi hp

ft3/sec gPm -

Ibf lbm/ft3 -

-

"F Ib-ft oz-in Wsec inlsec none

ft

Conversion

a Conversion factor x English units = metric units. Dimensions are not used. Values will depend on units used in formula.


Table 1.3.2 - Subscripts

Term I Subscript Term I Subscript Term 1 Test condition or

model

2 Specific condition or prototype

a Absolute

atm Atmospheric

b Barometric

d Discharge

dvr Driver input

9 Gauge

max Maximum

min Minimum

mot Motor

ot Operating temperature

OA Overall unit

P Pump

seal oil pressure in the lantern ring should be held to a minimum of 175 kPa (25 psi) above stuffing-box pressure. Mechanical seals must be chosen specifi- cally for the oil, temperature, pressure and speed.

The materials used for the construction of hot oil pumps should have a uniform coefficient of expansion and should be selected with particular reference to the corrosive nature of the oil, as well as the actual pumping temperature.

Due to the high pumping temperature, the support of the pump should be arranged in such a manner as to permit expansion of the pump casing without adversely affecting the coupling alignment.

API Standard 610 Centrifugal Pumps for General Refinery Service may be used for more information.

It is important that the suction and discharge piping be supported to avoid pipe strains being imposed on pump nozzles. The unit must be aligned at the operating temperature.

1.3.3.2.3 Volatile liquid pump

Pumps for handling volatile petroleum products, or other liquids having similar properties, are commonly termed volatile liquidpumps.

The determination of the net positive suction head available (NPSHA) for pumps handling volatile, multi- component liquids such as gasoline should be based, whenever possible, on the true vapor pressure of the particular liquid at the actual pumping temperature. The NPSH required by a pump at a given flow is a

s suction 1 t Theoretical 1 v Velocity

VP Vapor pressure w Water

function of the individual pump proportions and of the liquid pumped. The NPSH available must exceed the NPSH required by the pump and can be established correctly only when the true vapor pressure is known.

For refinery process applications, the true vapor pressure is usually available. For the pumping of finished petroleum products, the Reid vapor pressure is usually the only information available. This is the vapor pressure determined by the use of apparatus and procedure corresponding to the ASTM Standard D-323. Because of certain inadequacies of the test procedure, Reid vapor pressures are generally significantly lower than the true vapor pressures. Precautions must therefore be taken when the NPSH available must be determined on the basis of the Reid vapor pressure. If the commercial grade of the liquid handled is known, the use of one of the standard handbook correction charts for conversion of Reid vapor pressure to true vapor pressure is indicated. Also, see Section 1.3.4.1.16.4 and Figure 1.69.

The suction piping should be arranged to avoid any accumulation of vapor and provision should be made to allow self-venting of vapors by venting the first stage impeller suction eye, except where the suction nozzle is in a vertical position and facing upwards.

Since the suction pressure may vary over a wide range and the liquid pumped is frequently flammable or toxic, the stuffing-box may require the use of a mechanical seal, or, if packed, the use of one or more of the following elements: water jacketing, bleed-off connection, lantern ring for an oil or grease seal, or smothering- type gland.


The materials of construction should be selected with due regard to any corrosive action of the liquid pumped.

1.3.3.3 Transfer pumping

This service is normally a part of a process where a fluid is transferred from one location or process to another in a given plant. The type of pumps used will vary with the duty involved as will construction details and materials of construction.

1.3.3.4 Mine dewatering

Pumps used for handling acid or gritty mine water and1 or abrasive mixtures, slush, etc., are commonly termed mine pumps.

The pump should be liberally designed, with a heavy casing wall having ample corrosion allowance, and with provisions to keep corrosive liquids from the pump shaft. The design should provide for easy renewal of parts subject to corrosion or wear. The materials of construction for parts in contact with the liquid pumped must be selected for maximum resistance to corrosion and erosion.

1.3.3.5 Well pumping

Installation of centrifugal pumps with the suction supply water in a well below the ground surface on which the pump is located is possible when the pumping water level is close enough to the pump for atmospheric pressure to provide the pump's NPSH required. The "draw down" of the well must be known at the pump's maximum rate of flow. For a pump that is not self-priming, the suction pipe may be equipped with a foot valve, or an ejector may also be used to fill the suction pipe and pump casing. Automatic unattended operation is rarely successful with the installa- tions as described unless automatic priming systems are installed. A self-priming pump's casing must be filled with water before it is started. It is important to ensure that air leaks in the suction pipe are virtually eliminated for satisfactory operation.

1.3.3.6 Irrigation service

Centrifugal pumps in this service provide water either to open ditches for gravity flow to the points of application or to sprinkler systems of various types. The suction supply varies: it can be a well, a pond, a lake, a river or stream, or a distribution main under pressure (sometimes from a vertical pump). The pump may be

of the single suction or double suction type, with the impeller enclosed or semi-open. A suitable suction strainer is normally used to avoid clogging problems in either the pump or the sprinkler system. Single stage pumps normally supply the necessary head. Packing or mechanical seals may be used. Drivers are normally either induction motors or internal combustion engines.

1.3.3.7 Pumps for steam power plants

1.3.3.7.1 Steam electric power plants

Steam power plants convert nuclear energy or organic energy, in the form of coal, oil or gas, into electrical energy through the generation and expansion of steam from a high pressure to a low pressure in a prime mover, typically a steam turbine. When the electrical output of the generating plant is distributed for general sale, the plant is referred to as a central station. If the plant is operated by a manufacturing company that takes the output for its own use, it is referred to as an industrial plant.

Figure 1.47 diagrams a simple steam power cycle. A noncondensing plant discharges the steam from the turbine at an exhaust pressure equal to or greater than atmospheric pressure. A condensing plant (as shown in Figure 1.47) exhausts steam from the turbine into a condenser at a pressure less than atmospheric pressure. Central station plants are condensing plants because their sole output is electric energy. A reduction in the exhaust pressure at the turbine decreases the amount of steam required to produce a given quantity of energy. Industrial plants are noncondensing plants because large quantities of low pressure steam are required for manufacturing operations. The power required for operation of a manufacturing plant may be obtained as a by-product by generating steam at high pressure. This steam is expanded in a prime mover to the back pressure at which the steam is needed for manufacturing processes.

Figure 1.48 diagrams a coal-fired, condensing-type steam power plant, and identifies major plant compo- nents. The steam generating unit consists of a furnace, in which the fuel is burned, a boiler, supefheater, and economizer, in which high-pressure steam is generated, and an air heater in which the loss of energy due to combustion of the fuel is minimized. The boiler consists of a drum and a bank of inclined tubes connected to the drum. A water level is maintained at about the midpoint of the drum to permit separation of the steam from the water. Water circulates from the drum through the tubes and back to the drum. Part of

. . . .


Turbine

11 Bleed -- 11 11

Condenser Water

Circulating pump Condensate

pump

-i' - Feedwater -

Boiler 0 w

Boiler Feed Pump

Figure 1.47 - Diagram of a simple steam power cycle

Flue gas to chimney 4

Dust collector h

Figure 1.48 - Diagram of a typical condensing steam power plant


the water in the tubes is evaporated by the flow of furnace hot products of combustion across the tubes. The furnace walls are lined with tubes that are also connected to the boiler drum to form very effective steam generating surfaces. The steam separated from the water in the boiler drum flows through a superheater (essentially a coil of tubing surrounded by the hot products of combustion). The temperature of the steam increases in the superheater to as much as 425 to 600C (800 to ll0O0F) before it is piped to the turbine.

An economizer may be used to recover part of the energy in the gaseous products of combustion that leave the boiler tube bank at a relatively high temperature and discharge to the chimney. The economizer consists of a bank of tubes through which the boiler feedwater is pumped on its way to the boiler drum. This feedwater will be at a temperature considerably below that of the water in the boiler tubes. The temperature of the products of combustion may be reduced in the economizer to less than the boiler exit-gas temperature. A further reduction in flue gas temperature can be achieved by passing the products of combustion through an air heater (heat exchanger) cooled by the air required for combustion. This air is supplied to the air heater at normal room temperature and may leave the air heater at 200 to 315C (400 to 600F), thus returning energy to the furnace which would otherwise be wasted. The products of combustion are usually cooled in an air heater to an exit temperature of 135 to 200C (275 to 400F), after which they may be passed through a dust collector (to remove objectionable dust) and an induced-draft fan to the chimney. The function of the induced-draft fan is to pull the gases through the heat transfer surfaces of the boiler, superheater, economizer and air heater and to maintain a pressure in the furnace that is slightly less than atmospheric pressure (to eliminate leakage into the boiler mom). A forced- draft fan forces the combustion air to flow through the air heater, duct work and burner into the furnace. If both a forced-draft fan and an induced-draft fan are used in combination, the system is called balanced draft.

The diagram of a condensing steam power plant (Fig- ure 1.48) shows the coal being fed into the system by use of an overhead raw-coal bunker, where it flows by gravity through a feeder. In the pulverizer, the coal is ground to a fine dust. Some of the hot air from the air heater is forced through the pulverizer (mill) to dry the coal and pick up the finely pulverized particles and carry them in suspension to the burner. They are then mixed with the air required for their combustion and discharged into the furnace at high velocity to promote

good combustion. The high-pressure, high-temperature steam from the boiler is expanded in a steam turbine which is connected to an electric generator. Three to 5 percent of the output of the generator is needed to light the plant and to operate the motors required for pumps, fans, etc. in the plant.

In a central station plant, the exhaust steam from the turbine is delivered to a condenser to turn it into water at the lowest possible pressure. The condenser is a large, gas-tight chamber filled with tubes through which cold water is pumped. For normal operation, 725.000 kg (800 tons) of cooling water are required in the condenser for each 900 kg (1 ton) of coal burned in the furnace. This means that large power plants must be located on lakes, rivers or on the seacoast. Turbine exhaust steam is condensed because:

it was distilled in the boiler and is, therefore, free of scale-forming material and should be retained in a closed system,

the efficiency of the plant is increased substantially by reducing the exhaust pressure at the turbine to as low a pressure as possible.

It is estimated that a reduction in the exhaust pressure of just 3.5 kPa ('h psi) will reduce the coal consump- tion of the average plant by as much as 4 to 5 percent.

Condensed steam, which is at a temperature of 22 to 38C (70 to 10O0F), is pumped from the condenser by a condenser hotwell pump and discharged through several feedwater heaters to a boiler feed pump which delivers water through an economizer to the boiler. Figure 1.48 shows a high-pressure heater, an interme- diate-pressure heater and a low-pressure heater, all supplied with steam that extracted from the turbine at appropriate pressures after having done some work by expansion to the extraction pressure in the turbine. These are closed heaters. Figure 1.49 diagrams a closed feedwater cycle where the boiler feed water flows through tubes in the heaters and never directly contacts the steam extracted from the turbine. The condensed steam in a closed heater is collected and returned to the boiler water system (see Figure 1.49). Direct contact heaters would have thermodynamic advantages, but a separate pump would be required for each heater. The use of a group of closed heaters (as in Figure 1.49) permits a single boiler feed pump to discharge through all the heaters and into the boiler. Many power plants are based on a compromise system which uses one direct contact heater (which also provides for feedwater deaeration) and several closed- type heaters located both upstream and downstream


of the direct contact heater and the boiler feed pump. used, the closed cycle system uses either the con- Such a cycle is termed an open cycleand is diagrammed denser hotwell or a separate vessel for deaeration. All in Figure 1.50. When no direct contact heaters are the heaters are of the closed type.

+W Steam - Water Generator

- \

Condensate

Closed Closed Closed Closed - Heater -C Heater Heater Heater 4

No. 4 No. 3 NO. 2 No. 1 1.4 Boiler Feed Pump

Figure 1.49 -Diagram of a closed feedwater cycle

+ Steam - Water Generator

- \

Steam Turbine

I I I I I I I I c o N D tloller

A

V

I) V Condensate Pump

Closed Closed Direct Closed - Heater .C Heater Contact - Heater 4 Heater

No. 4 No. 3 No. 2 No. 1

t Boiler Feed Pump

:igure 1.50 - Diagram of an open feedwater cycle with one deaerator and three closed heatel


1.3.3.7.2 Power plant pumps

There are dozens of pump applications in conventional (fossil fuel) steam power plants. Most of these applications fall into the "miscellaneous" category, which includes such services as chemical feed, fuel oil, lubri- cating oil, fire protection, heating/ventilatinglair-condi- tioning, service water and support systems (such as ash sluicing, acid cleaning and hydrostatic pressure test pumps). The major categories include boiler feed, boiler feed boosting, condensate, condenser circulating, boiler circulating, and heater drain.

1.3.3.7.3 Boiler teed pumps

The type of boiler feed pump required by a generating plant is determined by the maximum boiler flow (capacity), the suction conditions (NPSHA), total pressure (head) required to be generated, and the operating temperature.

For low flow, low-pressure boiler feed systems, it may be possible to fulfill flow and head requirements with a single stage pump. In most cases, pressure (head) requirements are such that multistage pumps are necessary. In these cases, the pump can be one of several types and construction:

Low- to medium-pressureltemperature systems may require a pump of ring-section const~ction, where the individual stages are made up of impel- len and segmental rings (or casing sections, which include collectors to lead the flow from one stage to another), held together with tie rods. End heads contain the pump suction and discharge nozzles (see Figure 1.21 in ANSIIHI 1 .l-1.2). Medium-pressurehemperature systems may require axially split or ring-section pumps. Axially split pumps, unlike the ring-section pumps described above, may be of either back-to-back or in-line impeller construction and use cast casings, the lower half of which contains the pump suction and discharge nozzles. These pumps can be of either diffuser or volute construction. A back-to-back impeller pump design with volute construction is shown in Figure 1.20 in ANSIIHI 1 .l-1.2.

Higher pressureltemperature systems require the use of pumps with confined, controlled-compression gasketed joints. This can be accomplished by selecting pumps of either barrel or ring-section design to ensure containment of the high-pressure1 high-temperature boiler water, and to resist the considerable nozzle loads that can be imposed on

the pump as a result of temperature changes. Barrel-type pumps (see Figure 1.22 in ANSllHl 1 .l-1.2) are often chosen for ease of maintenance and the double case construction feature.

The user must determine the pump type that is appropriate for the system. Such decisions as pump construction (axially split, radially split casing, ring-section or barrel casing), rotor construction (back-to-back rotor arrangement or in-line rotor arrangement, with balance drum or balance disk), bearing type and pump support system requirements are usually made in conjunction with the pump manufacturer and take into account the manufacturer's specific installation and service experience.

A key factor in pump selection for demanding boiler feed service is rotor hydraulic axial balance. Two types of rotor construction need to be considered: in-line impellers and opposed impellers. With in-line impellers, the hydraulic axial thrust of the impellers is usually countered by a balancing device: either a balance disk or a balance drum, or sometimes a combination of both.

The advantages of a balance disk design may include reduced leakage (better volumetric efficiency) and the ability of the disk to compensate for wear and the amount of thrust that requires balancing. The disk is referred to as a "self-compensating" balancing device, and may be utilized to exclude an axial thrust bearing in certain designs, thus reducing initial cost and simpli- fying rotor construction and assembly.

The balance drum does not compensate for changes in thrust imposed on it, and it typically exhibits more leakage loss than a balance disk. The advantage of the balance drum over the balance disk is in the open- ness of its running clearance. For pumps in systems where severe upsets may occur, or where foreign material is continuously present, balance drums (with their larger running clearances) may prove less sensi- tive (less susceptible to damage) than balance disks. Bearing types vary from simple rolling element bearings (either ball or roller) to more sophisticated hydrodynamic versions which require support lubrication systems. Ball and roller bearings are usually selected for pumps with power requirements less than 1500 horsepower up to 3600 rpm. Pumps operating at higher speeds or higher horsepower are usually equipped with hydrodynamic radial and thrust bearings with force-feed lubrication support systems.


1.3.3.7.4 Boiler feed booster pumps

Boiler feed booster pumps are used to provide pressure to the feed pumps to meet their NPSH requirements and avoid cavitation. As the size and speed of boiler feed pumps has increased, the NPSH requirements have increased as well. It is not practical to install the direct-contact heaters from which feed pumps take their suction at sufficient elevation to provide adequate NPSHA without "boosting" the suction pressure to the feed pumps. The suction pressure is increased by utilizing low speed booster pumps ahead of the feed pumps.

Boiler feed booster pumps are generally of the single stage, double suction design (refer to ANSIIHI 1.1 -1.2 Figures 1.18 for axially split case and 1.19 for radially split case versions of this design configuration) and operate at lower speeds than the feed pumps, typically at four-pole motor speeds. The NPSH required by the booster pumps is much lower than that required by the feed pump it supplies. It is not unusual for the NPSH requirements of large, high speed boiler feed pumps to be in excess of 60 m (200 ft). Such requirement is much more than could be economically provided by elevation differences from feedwater heater placement to the feedwater pump.

1.3.3.7.5 Condensate pumps

Condensate pumps take suction from a condenser hotwell and discharge either to a deaerating heater in an open feedwater system (see Figure 1.50) or directly to the suction of a boiler feed pump in a closed system (see Figure 1.49). Condensate pumps operate at very low absolute suction pressures. Because it is desirable to locate the condenser hotwell as low as possible to minimize the elevation of the power plant, the NPSH available is usually extremely low. This may require the use of a deep pit for the condensate pump. The NPSHA, with absolute pressures in the condenser near zero, is only the submergence (or elevation) between the water level in the condenser hotwell and the centerline of the pump impeller (first stage impeller for multistage pumps). This value could be as low as 0.6 to 1.2 m (2 to 4 ft), which means that friction losses between the condenser hotwell and the pump suction must be kept to an absolute minimum to avoid reducing NPSHA further. To minimize friction losses, calculated velocities in the suction piping and within the suction can of vertical pumps should be no more than 1.2 mls (4 ftls). Condensate pumps can be either horizontal or vertical, single or multistage, depending on the system

head requirements. Because of the low NPSHA, horizontal pumps operate at relatively low speeds, from 1800 rpm for low flow requirements to 900 rpm or even less for higher flow requirements. Vertical can-type pumps (see Figure 2.6, ANSIIHI 2.1-2.2), which can be installed below ground and attain higher values of submergence of the impeller (higher NPSHA), can operate at higher speeds. Vertical can-type pumps are available with single and double suction first stage impellers and typically operate to 3600 rpm for low flow applications and 1200 rpm for higher flow requirements. Condensate pumps are designed or arranged such that they have discharge pressure (or at least a positive pressure above atmosphere) on the seal chamber (or stuffing box) to prevent air from entering the pump. If desired, pressure can be reduced through a throttle bushing at the bottom of the stuffing box and through an orifice back to suction. To prevent air leakage into an idle pump, the seal cages of multipe pumps can be piped together and connected to a common pump discharge header. It is standard practice to vent the suction chamber back to the condenser above the water level to minimize vapor entrainment.

1.3.3.7.6 Condenser circulating pumps

Condenser circulating pumps take cool water fmm a river, lake, stream or a cooling tower basin and circulate it through the condenser to condense exhaust steam from the main turbines. The pumps work against low to moderate heads (typically fmm 25 to 45 m [80 to 150 ft.]) and are installed to operate in parallel. These pumps can be added to or removed from service as heat load and demand for cooling water varies (a function of ambient temperature and plant load). Circulating pumps may be of either horizontal or vertical construction. The horizontal circulating pumps are low speed, axially split, single stage, double suction volute designs (see ANSIIHI 1.1-1.2 Figure 1.18). They are located in a dry pit which allows full access for servicing, dismantling and inspection. The vertical circulating pumps are of wet pit design (see ANSIMI 2.1-2.2 Figures 2.8 and 2.9), which means they are fully submerged in the water pumped. They employ a long pipe column which supports the submerged pumping element and the vertical driver is mounted on the top. Some vertical wet-pit designs allow removal of the pumping element without dismantling the pump casing or piping; these are referred to as "pull-out" designs. An alternative to the wet pit design is a dry pit, where the vertical pump operates surrounded by air. Single stage double suction pumps (as shown in ANSIIHI 1 .l-1.2 Figure 1.18) are sometimes mounted


vertically in a dry pit as well. Actual pump type selection is determined by plant layout and the experience of the plant designers and operators.

1.3.3.7.7 Boiler circulating pumps

Boiler circulating pumps circulate water within the boiler to enhance boiler operation. They take suction from a header connected to several downcomers from the bottom of the boiler drum and discharge through additional tube circuits. This means the water pumped is at boiler temperature and pressure. The pumps must develop only enough head to overcome the friction of the tube circuits. Boiler circulating pumps are designed for high temperature (usually between 150 and 315C [300 and 600F], depending on boiler size and rating), and high pressure (corresponding to boiler temperature and water vapor pressure). This combination of high temperature and pressure results in sealing conditions that require special sealing devices.

For small boilers, with relatively low temperatures and pressures, conventional overhung pump designs (see Figure 1.14) may be suitable for boiler circulating service. Because of the relatively low head requirements, the pumps are single stage with single suction impellers and a single seal chamber. This creates a problem of unbalanced axial thrust which may require special pump bearing systems or balancing arrangements. A solution is to utilize pumps of wet motor construction, where the pump and the motor are inside the pressure vessel, eliminating sealing and unbalanced axial thrust issues. These special pumps are welded into the boiler piping. For higher temperatures to 365C (685F) and pressures from 12,400 to 19,300 kPa (1800 to 2800 psi), special pump designs are required. 1.3.3.7.8 Heater drain pumps

Condensate from closed heaters (see Figure 1.49) is cascaded from the heater drain to the steam space of a lower pressure heater where it is flashed to steam. After the lowest pressure heater, the condensate in the heater drain is pumped back into the feedwater cycle. Because the pump takes suction from the heater hotwell where the pressure is low, this service is referred to as "low-pressure" heater drain service. In an open feedwater cycle, the drains from heaters located beyond the deaerator are cascaded back to the deaerator. The deaerator is located above the closed heaters and "high-pressure" heater drain pumps are used to transfer these drains to the deaerator and overcome static head and system frictional losses.

High-pressure heater drain pumps are subjected to more severe operating conditions than even the boiler feed pumps. Their suction pressure and temperature are generally higher, and the available NPSH is generally limited. They experience. more severe transients than the feedwater pumps, primarily because of the extremely limited NPSHA. Heater drain pumps are low speed, heavy duty designs. They may be either single or multistage, depending on pressure and flow requirements of the particular system. Single stage end suction pumps of the heavy duty process type (see ANSllHl 1.1-1.2 Figure 1.14) are popular for both low and high pressure services. Where NPSHA is very low, or head requirements exceed that of a single stage pump, vertical can pumps (see Figure 2.6, ANSIIHI 2.1-2.2) are sometimes utilized. Heater drain pumps are vented to an appropriate heater steam space to release any entrained vapors.

NOTE: Pump types other than those discussed may be suitable for the various applications highlighted.

1.3.3.8 Fire pumps

Pumps currently used today for fire protection in build- ings are of the centrifugal variety and provide water to a sprinkler andlor standpipe system. NFPA (National Fire Protection Association) issues a document titled "Standard for the Installation of Centrifugal Fire Pumps," which provides a national guideline for the selection and installation of centrifugal pumps for fire protection. A "Technical Committee on Fire Pumps," consisting of a broad range of interested parties involved with fire protection, reviews and updates this document (referred to as pamplet NFPA-20) on a three-year cycle.

NFPA published its first standard for automatic sprin- klers in 1896, and through the workings of the 'Techni- cal Committee on Fire Pumps," each edition of NFPA-20 has incorporated appropriate provisions to cover new developments and has omitted obsolete provisions. NFPA-20 1996 has been approved by ANSI and is used not only as a national standard but is accepted internationally as well.

Information provided within the NFPA-20 standard regarding the installation requirements for centrifugal fire pumps is based upon sound engineering princi- ples, test data, and field experience. The standard includes single stage and multistage pumps of horizontal or vertical shaft design with guidelines being established for the design and installation of these pumps, pump drivers and associated equipment.


Fire pumps have rated flow rates ranging in discreet flow increments from 6 m3/h (25 gpm) through 1135 m3/h (5000 gpm), with net pressures starting from 275 kPa (40 psi) and currently progressing through 4410 kPa (640 psi). In order for a centrifugal pump to be used as a fire pump it must meet stringent mechanical and hydraulic requirements witnessed and certified by Underwriters Laboratory (UL) and Factory Mutual (FM), two independent testing agencies. These testing agencies have established (with input from industry experts) certain engineering requirements that a pump must be capable of meeting before it can be listed or approved as satisfactory for fire service. The "Authority Having Jurisdiction" (AHJ) is the organization, office, or individual responsible for approving equipment such as a fire pump when used for the protection of life and property.

DouMe suction axial split case pumps, close-coupled vertical in-line pumps, and horizontal end suction pumps can be used for all fire pump ratings 57 m3/h (250 gpm) and higher. If an installation has a static suction lift, then a vertical turbine type pump must be utilized. The primary drivers for fire pumps are electric motors or diesel engines and almost all are started automatically.

1.3.3.9 Pumps used as hydraulic turbines

Centrifugal pumps of all sizes, types and specific speeds may be operated in reverse rotation as hydraulic turbines.

While running in the turbine mode, the performance characteristics of a PAT (pump as turbine) differ significantly from pump operation. See Figure 1.51. The applied head is usually constant, so the other parame- ters are shown as they vary with speed. Thedischarge nozzle of the pump becomes the inlet of the turbine, the suction nozzle of the pump becomes the outlet of the turbine, and the impeller of the pump, rotating in reverse direction, becomes the runner of the turbine. The impeller orientation to the casing is the same for both pump and turbine.

Reverse running pumps are an excellent alternative to conventional turbine designs. A common application is hydraulic power recovery turbines (HPRT). The potential for power recovery from high-pressure liquid streams exists any time a liquid flows from a higher pressure to a lower pressure in such a manner that throttling occurs. Reverse running pumps are used instead of throttling valves to recover the power in the

,I high-pressure liquid.

The installation costs for PATS are about the same as for an equivalent pump, and reliability and maintain- ability are also comparable. Because the efficiency of a pump operating as a turbine is comparable to the pump efficiency, the use of reverse running pumps as primary or secondary drivers becomes quite practical.

Pumps operating as turbines are classified by their turbine specific speed (NST), which is a quantity that governs the selection of the type of runner best suited for a given operating condition.

pp.= NST = nx-

H, '

Where:

NST = Turbine specific speed

n = Revolutions per minute

P, = Developed power in kW (hp) at best efficiency point (BEP)

Ht = Net head in meters (feet) per stage across the turbine

The values of NST will be slightly different between a pump operating as a pump and the same pump operating as a turbine. The rate of flow and total head at BEP will be greater for the turbine operation than for a pump operation. The amount of shift from pump performance depends on the specific speed and other design factors.

0 100 % Speed - 90 Full Speed RPM

Figure 1.51 -Turbine characteristics


For preliminary selection, a rough approximation procedure can be used to estimate the turbine performance from known pump performance.

Where:

Qt = Rate of flow as turbine

Qp = Rate of flow as pump

Hp = Total head as pump

H, = Total head as turbine

11 = Efficiency

Special care should be taken in PAT applications to ensure that the mechanical design of the unit will allow safe operation. Frequently these applications subject the PAT to increased mechanical stresses, torque, and speed levels beyond original pump design values. Additionally, the turbine characteristics are such that both hydraulic forces and torsional stresses increase with increasing rate of flow. All pumps applied as turbines should be subject to a careful calculation of combined stresses in shafts.

Pumps operated in reverse as turbines tend to have relatively narrow operating bands compared to vari- able nozzle turbines. At constant speed, the power developed and efficiency drop to zero at approximately 40 percent of the hydraulic turbine best efficiency rate of flow. See Figure 1.52. Energy must be added to the hydraulic turbine in order for it to rotate at the constant speed below this rate of flow. Changing the impeller diameter has little effect on adjusting the performance of a hydraulic recovery turbine. These facts, coupled with the difficulty in predicting hydraulic turbine performance from pump performance, results in some

Most centrifugal pumps are suitable and capable of uncertainty when applying a pump to a power recov- operating as turbines. Because of the reverse rotation, ery turbine application unless test data is avail- be sure that the bearing lubrication system will operate able on the specific pump running in reverse as a in reverse, and threaded shaft comDonents, such as

Lu,"Bm mu,

impeller locking devices, cannot lookn. Precautions should also be taken to ensure that the

he power output is the rotational energy developed PAT will operate without cavitation. The turbine indus- by the reverse running pump. Its value is calculated in try typically uses the terminology TREH (total required a similar manner as for a pump except for the Place- exhaust head) and TAEH (total available exhaust ment of the efficiency term. head) in place of NPSH. Total exhaust head is defined

Q x Hx s x q t Metric Pt =

366

Q x H x s x q t US units Pt = 3960

Where:

Pt = Power output from turbine - kW (hp) Q = Rate of flow - m3/hr (gpm) H = Total head in meters (feet) s = Specific gravity

q t = Efficiency of the turbine

SPEED CONSTANT

I

0 50 100 % Rate of Flow

Figure 1.52 -Turbine performance


as the total fluid energy at the impeller eye less the vapor pressure of the fluid.

Some of the other factors which affect the use of pumps as turbines are:

Runaway speed

Rate of flow at runaway speed

Required solids passage

Fluid-borne abrasives

Torque reversals during start-up or shut-down

Overspeed trip and control

1.3.3.1 0 General purpose service

1.3.3.10.1 Self-priming pump applications

Self-priming pumps are designed to have the following abilities: to prime themselves automatically after being initially filled, when operating under a suction lift; to free themselves of entrained gas without losing their prime and to continue normal pumping without atten- tion. Pumps in this class usually have single inlet impellers.

Self-priming centrifugal pumps have these additional features when compared to a centrifugal pump:

A reservoir, either integral with or external to the volute and impeller, to retain priming liquid. This reservoir is filled during the initial prime of the pump. The suction line itself is not filled. When the pump completes a pumping cycle and shuts down, the reservoir retains liquid for the next priming cycle.

A means of recirculating liquid. The majority of modern self-priming pumps have integral reser- voirs with internal recirculation, the most common being the recirculation from the pressure side of the volute back to the periphery of the rotating impeller. A less common method of recirculation directs the priming liquid back into the suction side of the pump.

An integral suction check valve to prevent the loss of liquid in the suction leg is common in many designs. Some designs allow for check valve fail- ure due to debris-laden water and will reprime with residual amounts of priming liquid.

Self-priming can also be accomplished in diffuser design centrigugal pumps used primarily for clear liquids. Closed impellers with suction side wearing rings can also be used.

Self-priming centrifugal pumps are commonly placed up to about 8 meters (25 feet) above the liquid level of the source. All suction connections must be air-tight. During initial start-up, the impeller rotation causes the liquid in the impeller and suction side of the pump reservoir to be forced to the discharge cavity via centrifugal force. Differential pressures cause the priming recirculation to start. The priming action reduces pressure in the impeller eye and allows atmospheric pressure on the liquid source to fill the suction line.

During priming, air in the discharge chamber sepa- rates up and out from the mixture while the heavier water continues to recirculate. It is important that the air in the discharge chamber have a means to escape either through the discharge pipe or an air release valve. This process continues to draw air from the submerged suction line until it is full of liquid and the pump goes to normal pumping.

The different designs of self priming pumps have limited and varied capabilities of priming against discharge heads. When a discharge check valve is used, or the discharge design can form a pressure trap, air release lines or valves may be necessary to get rid of air from the suction side.

Self-priming centrifugal pumps are frequently used for unattended service in industrial, construction dewatering, waste water and agricultural applications where manual priming is not practical during operation.

Most pumps are designed to accept the major modern drive sources through direct drive, flexible coupling or belt drives. The materials of construction are usually cast iron, steel, stainless steel or bronze, depending on the application.

Many manufacturers of self-priming pumps build units to conform to the specifications established by the Contractors Pump Bureau, an arm of the Construction lndustry Manufactures Association (CIMA). See Fig- ure 1.53. In these cases, the pumps may carry a CPB rating decal and are built to conform to CPB specifications. Other manufacturers build pumps that are closer in concept to the Chemical lndustry requirements and appear as shown in Figure 1.54.


1.3.3.10.2 Hydraulic pressure pump

These pumps are used for supplying water under pressure for scale r e m o ~ l from steel products and for operation of presses, leveling tables, hydraulic press service, elevators, etc.

The suction supply should be adequate to prevent parting of the liquid column during sudden demands for high rate of flow. If this situation occurs, an accu- mulator may be required.

The demand is frequently intermittent and the control valves are usually rapid in action. The sudden demand or cessation of demand causes accelerations and decelerations of water in the piping, resulting in pressure waves of great intensity. These waves are famil- iarly called "shock" or "water hammer." The waves originate at the point of valving and travel back through the line toward the pump.

To protect the pump against damage from shock, an air-ballasted alleviator is recommended. The alleviator should have a free liquid surface against which the shock waves cannot by-pass the alleviator. Alleviators mounted on side outlets of tees are of little value.

1.3.3.10.3 Sanitary pump

Pumps designed to handle foodstuffs and beverages are commonly called sanitary pumps. The materials of construction for parts in contact with the liquid pumped, including the stuffing box or shaft seal, are selected to prevent bacterial, chemical, color, or taste contamination. Materials such as stainless steel, monel, porcelain, glass, etc., are frequently used. San- itary pumps are constructed to permit ready access for cleaning, flushing, and draining. If the liquid to be pumped contains solids, the maximum size solid must be specified.

The user is cautioned that many states prescribe regulations regarding sanitary pumps. Adherence to such regulations is mandatory. The responsibility for deter- mining these requirements rests with the user.

1.3.3.1 1 Wastewater service (solids and nonclog) Pumps designed to assure maximum freedom from clogging when handling liquids containing solids or stringy materials are commonly called non-clog pumps. They are also designated as sewage or trash pumps.

Figure 1.53 - Self-priming pump - construction industry

Non-clog pumps are recommended for handling raw or unsettled sewage, activated sludge, industrial waste waters containing solids, and similar liquids where excessive clogging would othelwise be encountered. The largest solid sizes that the pump will be required to handle in normal operation must be specified. The term "sphere size" denotes the largest diameter ball which can be passed through the pump. Comminution andlor adequate bar screens must be provided to prevent large solids from entering the pump. When used, bar screen openings should be sized to prevent clogging from irregular-shaped solids.

Storm water andlor domestic sewage may be handled successfully by mixed flow and axial flow pumps, using the preceding guidelines.

For domestic sewage service, pumps built to the individual manufacturer's material specifications are ordinarily used. Corrosion-resistant and wear-resistant shaft sleeves and wearing rings are desirable for maxi-


mum life. Inspection openings in the casing or adja- cent piping, for access to the impeller, are recommended. Stuffing-boxes may be furnished with mechanical seals or packing, either water or grease lubricated. When water is used for the stuffing-box or wearing ring lubricant or flush, the supply line must be isolated from any potable water system.

If the pumpage is corrosive andlor abrasive, the materials of construction for parts in contact with the liquid should be selected for resistance to the effects of the pumpage.

1.3.3.12 Pulp and paper applications

1.3.3.12.1 Paper Stock

Consisting of a mixture of water and wood fibers in suspension, paper stock is created by a number of different methods, and from a number of different wood varieties. The pumpability of paper stock depends

Figure 1.54 - Self-priming pump - chemical industry


mainly on the characteristics of the raw material and the consistency of the stock.

Paper stocks are generally separated into three distinct consistency categories, namely low, medium and high.

Low-consistency stock usually refers to a class of products with 1-7% fiber content by weight. These paper stocks are normally handled by end-suction centrifugal pumps equipped with semi-open impellers and contoured wearplates.

Medium-consistency stocks are made of 8-15% paper fiber. The rheological properties of fiber-water suspen- sions in this range are dependent on the properties of the individual fibers and the viscoelastic network that they form. Special designs of centrifugal pumps are required to handle this type of paper stock. For example, some form of "shear generator" is needed at the inlet to create turbulence, and reduce the effective fluid viscosity. Special impeller design and air-extraction devices are also required to prevent airbinding.

An end-suction centrifugal pumping unit must be spe- cifically designed to handle medium-consistency stock mixtures without clogging the device, or dewatering the stock. A large suction-eye and unobstructed water- ways can be provided by an overhung, semi-open impeller design. This keeps the suction velocity low to promote smooth flow, avoid air binding and prevent separation of stock fibers from water. The contoured front surfaces of the impeller vanes interface with the replaceable wear plate. This arrangement provides a self-cleaning effect whereby the impeller resists clogging to improve its reliability.

High-consistency paper stocks contain more than 15% paper fiber, and are found in the bleaching operation. Centrifugal pumps cannot handle such high consistencies, and therefore, positive-displacement rotary units are used. Pmper suction-piping design has to be included to help this high solids mixture to enter the suction cavities of the rotary pump.

Normally two-screw or clove-rotor types of rotary pumps are used for handling high-consistency paper stock. Once the stock has been introduced into the suction area, the positive displacement principle is employed to force the product through the pump, and out the discharge opening.

Special rotor designs and clearances are often used to obtain the most-efficient pumping action. When extrane- ous material and air are entrained in high-consistency

paper stocks, there can be serious difficulty in handling these liquids.

A thick-wall casing design is used to allow for ample corrosion, and withstand reasonable piping loads commonly encountered in handling hot stocks. Large shaft diameters and heavy-duty bearings, mounted in a rigid, one-piece bearing frame, improve the unit's reliability in difficult services. The impeller-shaft assembly can be moved via an adjustment feature located on the thrust-bearing housing to maintain close clearances between the impeller and the wear plate, thus ensuring maximum operating efficiency. Some designs provide adjustability in the wear plate for the same purpose.

To resist corrosion from the process chemicals, different areas of the paper-making process require different materials of construction for the equipment. Cast iron, Types 316, 317 and 317L stainless steels, and Alloy 20 are commonly used in units handling paper stocks. These materials can also be used in various combinations to provide the corrosion resistance as well as mechanical strength.

1.3.3.12.2 Hydraulic performance correction

The many different paper stocks available and their varied characteristics make it difficult to predict the effect of a given type of paper stock on pump performance. Still, many tests have been conducted on different pumps and paper stocks to establish performance correction criteria, to relate water performance of a pump to predicted performance on various types and consistencies of paper stock. However, for accurate prediction this data is limited to the type of paper stock and type of pump from which the data was obtained.

Testing continues to this day to derive more-accurate correction data. For many applications of mid-sized to large-sized pumps, no performance correction is required for up to 6% stock consistency. Modern data indicates that in some cases, pumps smaller than those previously chosen can be used for paper stocks. Clearly, this data also suggests an improvement in efficiency of modern units. Refer to the pump manufacturer when precise performance correction data is required.

While corrections for consistency for up to 6% are not critical, the user must still make sure that air entrainment is taken into consideration. Also, optimum suction-conditions and adequate net positive suction head (NPSH) must be available to ensure that the desired

HI Centrifugal Pump Design and Application -2000

performance will be achieved on the given paper stock. The essential requirement is to get the stock to the impeller. To do so, every effort should be made to keep the suction piping as large and straight as possible.

1.3.3.13 Slurry service

Centrifugal slurry pumps may be used for inplant, process and pipeline applications where heads are not high enough to warrant the use of reciprocating or rotary units.

The other factors which affect the selection of centrifugal slurry pumps are:

- Rate of flow;

- Pressure;

- Abrasiveness (i.e., particle size, density, concentration, shape, hardness);

- Pump Performance (i.e., particle size, density, concentration, carrier, viscosity).

Pumps are commonly applied for rates of flow from 2 to 4500 m3/h (10 to 20,000 gpm) with 'heads up to 90 meters (300 feet) per stage. Pumps may be installed in series for higher head and severely abrasive applications.

There are many different slurry pump designs available to accommodate various industrial applications. Those applications include the pumping of solids encountered in mineral ore treatment, dredging, sewage handling, land reclamation, paper manufacture, solids transportation and chemical processing.

1.3.3.13.1 Performance changes pumping slurry

The characteristic performance curve of a centrifugal pump differs from its clear water performance when solids are included and the flow becomes two phase, i.e., the head and efficiency will decrease. The magni- tude of the reduction and the shape of the characteristic curve will depend mainly on solids size, volumetric concentration and density. The pump horsepower will increase directly with the slurry specific gravity. A nomograph relationship between concentration and specific gravity for aqueous slurries is shown on Figure 1.55.

The pump manufacturer will make allowances in the pump selection for head and efficiency reduction, provided the slurry characteristics are defined.

1.3.3.13.2 Non-settling slurries

Slurries with a narrow band distribution of small particles where the average size is usually less than 100 microns will be "non-settling" and behave as a Newto- nian liquid. Standard viscosity correction procedures can be used, provided the apparent viscosity of the slurry is known. See Figure 1.56 for typical performance characteristics. Cv = % solids by volume.

Non-settling slurries which have higher apparent vis- cosities such as pastes, filter cakes, etc., should be pumped at lower velocities to minimize friction losses in the system.

1.3.3.13.3 Settling slurries

Slurries with a distribution of larger particles exhibit "settling" and the particles and the liquid exhibit their own characteristics, since energy is dissipated due to liquid drag. See Figure 1.57 for typical performance characteristics.

The critical factor governing a system handling a watery slurry in which the solids have a much higher specific gravity than the carrier liquid is the settling rate and characteristic. Coarse solids with a high settling rate are carried in a centrifugal pump with many precautions to prevent plugging, draining and squeeze out.

In applying centrifugal slurry pumps to handle settling slurries, one must be certain that the head requirements of the system above the critical carrying velocity would be met by the pump. If the head produced is insufficient, the rate of flow is reduced and the solids will settle in the line. Since the head versus rate-of- flow curve of most slurry pumps has little slope, such an increase can make a large reduction in the volume pumped, further reducing the flow velocity and leading to plugging in the system pipe. This situation can usually be avoided by using conservative values for the slurry critical carrying velocity.

1.3.3.1 3.4 Materials of construction for slurry pumps

Pumps designed to resist abrasion are normally made of hard metals (abrasion-resistant cast irons and steels), elastomers or ceramics. As a general guideline, hard metals are often used in applications characterized by


large, sharp-edged solids, and elastomers for smaller b) Utilize pumping elements which combine soft and round-edged solids. Either high-chrome irons or elas- hard materials in such a fashion as to reduce tomers are used for their corrosion resistance. In spe- abrasion and provide resiliency; cia1 applications with low head requirements, solid ceramic-lined pumps are used for pumpages contain- c) Increase material thicknesses in areas of high ing fine material. wear;

Some pump design techniques to minimize wear are: d) Utilize hydraulic designs with specific speeds of 1400 or less.

a) Utilize pumping elements which are harder than the hardest slurry particles;

SS h

90 4 Solldl by volume

80

7'3

1.3

t, /

1.1

SO

1.5 1" / 1.6 /

30 1.7

10

2.1 Sm 5 Slurry

cw % SOlldS Speclllc by Welght Gravity

Figure 1.55 - Nomograph of the relationship of concentration to specific gravity in aqueous slurries

18


1.3.3.13.5 Rotational speed of slurry pumps

Speed is one of several contributors to wear rate. With abrasive solids, wear rate is generally proportional to relative velocity between the slurry and the pump elements to the power of two or three.

cv= 15%

Water .-

0 30% f W

g Input c -

Rate of flow

Figure 1.56 -Typical performance characteristics - non-settling slurries

Rate of flow

Figure 1.57 - Typical performance characteristics - settling slurries

Impeller tip speed as distinct from rotational speed is often used as a guide for wear in the selection of slurry pumps:

- for dirty water-type applications, limited to 40 m/s (1 30 Wsec);

- for medium slunies up to 25% solids concentration by weight and mean solids size of 200 microns, limited to 35 m/s (1 15 Wsec);

- for slurries with higher concentrations of solids and much larger solids size, restricted to 30 m/s (100 Wsec);

- pumps fitted with elastomeric impellers are commonly limited to 26 m/s (85 Wsec).

1.3.3.14 Liquids with vapor or gas

Two phase flow pumping applications include situa- tions where undissolved vapors or gases are being carried by the pumpage. One example is biological- fluid processing, such as the fermentation process used in yeast production. In this application, the process liquid is circulated from the bottom to the top of an aerator that injects large amounts of air into the process liquid. The fluid entering the pump may contain as much as 50% air by volume.

Oil production from wells often requires the pumping of crude oil that contains large amounts of natural gas mixed with the oil. In many cases, the inlet pressures for the pump range from 10,000 to 20,000 kPa (1500 to 3000 psi). Other applications are those where the inlet pressure is below atmospheric pressure. As a consequence, air can leak into the system, resulting in gas-liquid mixtures that must be handled by the pump. Even small amounts of air can cause problems because the air expands substantially under low pressure to increase its volume, particularly at the inlet of the pump impeller.

1.3.3.14.1 Effect of gas on performance

The most dramatic effect of gas or vapor on centrifugal pump performance is the complete blocking of the impeller inlet as the pump becomes "airbound." When this happens, the impeller acts as a centrifuge, and tends to separate the heavier liquid from the gas that builds up at the impeller inlet. At low rates of flow, the liquid flow cannot even carry the air through the impeller, and the gas bubble grows until it completely fills


the impeller eye (suction side). The result is complete cessation of liquid flow.

Even when small amounts of gas are carried through the impeller, the liquid rate of flow and pump discharge pressure are reduced (Figure 1.58). This reduction is the result of the blockage of the flow by the gas, and a reduction in developed pressure due to the reduced specific gravity of the pumped mixture. When the specific gravity of liquid alone is used to convert pressure to head, a lower head measurement is indicated.

It can be seen from Figure 1.58 that even with small percentages of air, the unit stops pumping liquid due to accumulated air in the im~eller when o~eratina near the shut-off condition of the pump. High velocitie;at higher rates of flow can carry with it higher percentages of gas. Therefore, when gas entrainment is a potential problem, pumps should be operated at or beyond the BEP rate of flow specified by the manufacturer.

Inducers or inlet boosters (Figure 1.59) are devices designed to benefit the functioning of the impeller in that they increase the fluid pressure before the mixture enters the pump. This increase in pressure reduces the volume of the air, thereby reducing its negative effect on the impeller performance. Since inducers generate low levels of pressure, they will have little benefit on high suction pressure applications.

Laboratory tests have shown that pumps with higher specific speed (above 3500 [3,000]) are affected less by the presence of gas than those with low specific speed (below 1150 [I ,0001). In some cases, it may be helpful to use a high specific speed booster pump in series with a low specific speed pumping unit in order to minimize the effect of the gas.

Open impellers may handle gas better than closed impellers, particularly with large clearances between the impeller and the casing. The large clearance gen- erates turbulence which helps prevent the accumulation of large gas pockets.

Another helpful action is to provide a gas vent at the pump inlet. The suction pipe should be sized about twice as large as the flange at the pump inlet in order to keep inlet velocities low. A vent connection should be located at the top of the pipe, close to the pump so that gas can escape back to the source.

If the pump takes suction from a closed tank, it may be possible to pressurize the inlet, thereby reducing the volume of entrained gas, or turn some vapors back to liquid. Where vapor is the primary problem, subcooling of the inlet pipe may be helpful. This will also tend to turn vapor back to liquid, and thus reduce the volume o

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