ANSI HI 9.6.3-1997

9 Sylvan WayParsippany, New Jersey07054-3802 www.pumps.org

AN

SI/H

I9.

6.3-

1997

ANSI/HI 9.6.3-1997

American National Standard for

Centrifugal and Vertical Pumpsfor Allowable Operating Region

http://www.pumps.org

Copyright © 2000 By Hydraulic Institute, All Rights Reserved.

This page intentionally blank.


ANSI/HI 9.6.3-1997

American National Standard for

Centrifugal and Vertical Pumpsfor Allowable Operating Region

Secretariat

Hydraulic Institute

www.pumps.org

Approved August 20, 1997

American National Standards Institute, Inc.

Recycledpaper



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

Consensus is established when, in the judgement of the ANSI Board of StandardsReview, substantial agreement has been reached by directly and materially affectedinterests. Substantial agreement means much more than a simple majority, but not nec-essarily 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 doesnot in any respect preclude anyone, whether he has approved the standards or not,from manufacturing, marketing, purchasing, or using products, processes, or proce-dures not conforming to the standards.

The American National Standards Institute does not develop standards and will in nocircumstances give an interpretation of any American National Standard. Moreover, noperson shall have the right or authority to issue an interpretation of an AmericanNational Standard in the name of the American National Standards Institute. Requestsfor interpretations should be addressed to the secretariat or sponsor whose nameappears on the title page of this standard.

CAUTION NOTICE: This American National Standard may be revised or withdrawn atany time.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

Published By

Hydraulic Institute9 Sylvan Way, Parsippany, NJ 07054-3802

www.pumps.org

Copyright © 1997 by Hydraulic InstituteAll rights reserved.

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

Printed in the United States of America

ISBN 1-880952-24-6

AmericanNationalStandard



iii

ContentsPage

Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v

9.6.3 Allowable operating region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

9.6.3.1 Preferred operating region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

9.6.3.2 Allowable operating region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

9.6.3.3 Factors affecting AOR. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

9.6.3.3.1 Temperature rise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

9.6.3.3.2 Bearing life. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

9.6.3.3.3 Shaft seal life . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

9.6.3.3.4 Vibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

9.6.3.3.5 Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

9.6.3.3.6 Internal mechanical contact. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

9.6.3.3.7 Shaft fatigue failure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

9.6.3.3.8 Horsepower limit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

9.6.3.3.9 Liquid velocity in casing throat. . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

9.6.3.3.10 Thrust reversal on impeller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

9.6.3.3.11 NPSHA margin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

9.6.3.3.12 Head rate of flow curve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

9.6.3.3.13 Suction recirculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Appendix A Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9


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v

Foreword (Not part of Standard)

Purpose and aims of the Hydraulic Institute

The purpose and aims of the Institute are to promote the continued growth andwell-being of pump manufacturers and further the interests of the public in suchmatters as are involved in manufacturing, engineering, distribution, safety, trans-portation 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 thepublic;

c) To appear for its members before governmental departments and agenciesand 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 servicesfor its members or individual persons as distinguished from activities toimprove the business conditions and lawful interests of all of its members.

Purpose of Standards

1) Hydraulic Institute Standards are adopted in the public interest and aredesigned to help eliminate misunderstandings between the manufacturer,the purchaser and/or the user and to assist the purchaser in selecting andobtaining the proper product for a particular need.

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

Definition of a Standard of the Hydraulic Institute

Quoting from Article XV, Standards, of the By-Laws of the Institute, Section B:

“An Institute Standard defines the product, material, process or procedure withreference to one or more of the following: nomenclature, composition, construc-tion, dimensions, tolerances, safety, operating characteristics, performance, qual-ity, rating, testing and service for which designed.”

Comments from users

Comments from users of this Standard will be appreciated, to help the HydraulicInstitute prepare even more useful future editions. Questions arising from the con-tent of this Standard may be directed to the Hydraulic Institute. It will direct allsuch questions to the appropriate technical committee for provision of a suitableanswer.

If a dispute arises regarding the contents of an Institute publication or an answerprovided by the Institute to a question such as indicated above, the point in ques-tion shall be referred to the Executive Committee of the Hydraulic Institute, whichthen shall act as a Board of Appeals.


vi

Revisions

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

Scope

This standard applies to centrifugal and vertical pump types. It describes theeffects of operating a centrifugal or vertical pump at rates of flow that are above orbelow the rate of flow at the pump’s best efficiency point.

Units of Measurement

Metric units of measurement are used; corresponding US units appear in brack-ets. Charts, graphs and sample calculations are also shown in both metric and USunits.

Since values given in metric units are not exact equivalents to values given in USunits, it is important that the selected units of measure to be applied be stated inreference to this standard. If no such statement is provided, metric units shall govern.

Consensus for this standard was achieved by use of the CanvassMethod

The following organizations, recognized as having an interest in the standardiza-tion of centrifugal pumps were contacted prior to the approval of this revision ofthe standard. Inclusion in this list does not necessarily imply that the organizationconcurred with the submittal of the proposed standard to ANSI.

Agrico Chemical CorporationAmerican Society of Heating,

Refrigerating & Air ConditioningEngineers

American Society of MechanicalEngineers

Amoco Oil CompanyBlack & VeatchBP AmericaBrown & CaldwellCamp Dresser & McKee, Inc.CH2M HillDe Wanti & StowellDow ChemicalDuPont EngineeringDurametallic CorporationElectric Power Research InstituteFleet Tech. Supt. CenterFlorida Power CorporationFoth & Van DykeGT Exporters

Hydraulic InstituteInstitute of Paper Science & Tech.John Carollo EngineersJohn Crane, Inc.Malcolm Pirnie, Inc.Marine Machinery Assoc.Material Tech. Inst. of ChemProMontana State UniversityMontgomery WatsonMobil Technology Co.Naval Surface Warfare CenterOWP&P ConsultantsOxy ChemicalRaytheon Engineers & ConstructorsStar EnterprisesState of California, Dept. of WaterStone & WebsterSummers EngineeringSysticon, Inc.Union Carbide CorporationUS Bureau Of Reclamation


HI Pumps – Allowable Operating Region — 1997

1

9.6.3 Allowable operating region

HI Pumps – Allowable Operating Region9.6.3.1 Preferred operating region

This standard describes the effects of operating a cen-trifugal pump at rates of flow that are above or belowthe rate of flow at the pump’s best efficiency point(BEP). These effects influence the life of pump compo-nents and therefore an understanding of them isessential to all concerned. Design characteristics forboth performance and service life are optimizedaround a rate of flow designated as the Best EfficiencyPoint (BEP). At BEP the hydraulic efficiency is maxi-mum, and the liquid enters the impeller vanes, casingdiffuser (discharge nozzle) or vaned diffuser in ashockless manner. Flow through the impeller and dif-fuser vanes (if so equipped) is uniform and free of sep-aration, and is well controlled. The flow remains wellcontrolled within a range of rates of flow designated asthe Preferred Operating Region (POR). Within thisregion the service life of the pump will not be signifi-cantly affected by hydraulic loads, vibration, or flowseparation.

Centrifugal Pumps: The POR for most centrifugalpumps is between 70% and 120% of BEP. For smallerpumps less than 4 kw (5 HP) the manufacturer mayrecommend a wider POR.

Vertical Pumps: Well controlled flow in higher specificspeed pumps occurs in a narrower flow range. Thusthe POR for vertical pumps is:

9.6.3.2 Allowable operating region

A wider operating range is termed the Allowable Oper-ating Region (AOR). The AOR is that range of rates offlow recommended by the pump manufacturer overwhich the service life of a pump is not seriously com-promised. Minimum bearing life will be reduced andnoise, vibration, and component stresses will beincreased when a pump is operated outside its POR.As a result, service life within the AOR may be lowerthan within the POR. It should be recognized thatwhile the calculated minimum bearing life may varysignificantly over the AOR, at any point within this

range the calculated minimum bearing life will allowtwo years of service.

The service life of any piece of mechanical equipmentis dependent on a large number of factors. This dis-cussion deals only with those factors related to operat-ing rates of flow and pump design. Other factors suchas proper equipment selection, installation, mainte-nance, and operation are not addressed here.

It is also assumed that the pumped liquid is a nonvis-cous, noncorrosive, pure liquid with no vapor, gas,suspended solids or abrasives. For other liquids thegeneral principles contained herein apply with quanti-tative modifications. Certain special liquid mixturesmay have other characteristics which affect the AOR.For example, the minimum rate of flow when pumpinga liquid which contains entrained air may be deter-mined by air separation at the eye of the impeller.

When a manufacturer’s recommendations deviate sig-nificantly from these guidelines, or a concern existsregarding the ability of the pump to operate reliably atthe specified rate of flow, a factory test should bespecified. Characteristics that should be monitoredduring the test include one or more of the following asappropriate:

– stability of rate of flow being pumped;

– bearing housing vibration;

– shaft vibration;

– motor vibration;

– bearing temperature;

– noise.

Acceptance criteria for the above shall be agreed to bythe producer and purchaser at the time the test isordered.

9.6.3.3 Factors affecting AOR

Following is a list of the factors that a pump manufac-turer considers when establishing the AOR. Within theAOR the manufacturer has determined that none ofthe factors exceeds limits that will severely impact theservice life of the pump. The factor that determines theupper or lower limits of the AOR will normally vary withpump type and specific design, and may not be evi-dent from the manufacturer’s literature. This list, and

Specific SpeedPOR

Metric US Unit

≤ 5200 ≤ 4500 Between 70% & 120% of BEP

> 5200 > 4500 Between 80% & 115% of BEP



2

the following discussion of each, is provided as an aidin understanding the acceptable operating limits:

– temperature rise;

– bearing life;

– shaft seal life;

– vibration;

– noise;

– internal mechanical contact;

– shaft fatigue failure;

– horsepower limit;

– liquid velocity in casing throat;

– thrust reversal on impeller;

– NPSHA margin;

– slope of the head–rate-of-flow curve;

– suction recirculation.

It should be noted that the design characteristics ofsmaller pumps may not be determined by load anddeflection criteria, but by manufacturing and standardhardware considerations. These scale factors oftenresult in smaller pumps being more robust than largerpumps with respect to the imposed loads. A manufac-turer often includes these effects in determining theAOR.

9.6.3.3.1 Temperature rise

ANSI/HI 1.3, Centrifugal Pumps for Design and Appli-cation, Section 1.3.3.2.4, provides a recommendedpractice for calculating the minimum thermal rate offlow. This rate of flow is dependent on the specificheat, the vapor pressure-temperature relationship ofthe pumped fluid, as well as the NPSHA/NPSHR ratio.Consequently the minimum thermal rate of flow isapplication specific.

9.6.3.3.2 Bearing life

Manufacturers will limit the AOR for pumps designedto operate continuously to operating conditions wherethe bearing life is equal to or greater than 17,500hours. Pumps designed for intermittent service may

have a shorter calculated bearing life. Vertical diffuserpumps and pumps with hydrodynamic bearings do notnormally have a calculated bearing life with respect torate of flow, but rate of flow limitations may be consid-ered in calculating bearing whirl and maximum loadrate of flow.

9.6.3.3.3 Shaft seal life

Excessive shaft deflection at the faces of a mechanicalseal will reduce the seal life. Most process pump man-ufacturers limit the AOR to operating conditions wherethe shaft deflection at the seal faces is 0.05mm (0.002in.) or less for pumps with rolling element bearings.Since most seal designs and all compression packedpumps permit greater deflections, the continuous rateof flow limits (both maximum and minimum) are appli-cation specific.

9.6.3.3.4 Vibration

The HI Standards specify the maximum allowablevibration for Centrifugal and Vertical pumps. Thesepumps typically exhibit a minimum vibration near theBest Efficiency Point, with increases in vibration athigher and lower rates of flow. Vibration levels exceed-ing the allowable limits are one criterion for establish-ing the AOR.

9.6.3.3.5 Noise

A certain amount of noise is expected from any pump.Pumps with higher energy levels usually operate withhigher noise levels. It is often found that, at higher andlower rates of flow, and lower NPSH margins, thenoise changes from a sound characterized as sandsliding down a chute, to one of gravel or rocks. Thechange in sound level is often not distinguishable on asound level meter, but the change in sound character-istic is detectable by the human ear. Gravel and rocksounds are usually caused by cavitation in the pumpsuction and may cause mechanical damage and canlimit the AOR. A noise test may be used to help evalu-ate the AOR.

9.6.3.3.6 Internal mechanical contact

Hydraulic loads originating in the impeller or casingproduce deflections in mechanical components. Theloads may be steady or varying, but usually change asthe operating rate of flow changes. As loads increase,deflections may become so large as to result in con-tact between rotating and stationary parts. This maynot be harmful if the parts are compatible (i.e., nongall-ing combinations of impeller and casing rings). Each



3

manufacturer evaluates their design and operatingexperience to determine if operating limits should beestablished.

9.6.3.3.7 Shaft fatigue failure

Hydraulic loads originating in the impeller or casingare transmitted through the shaft to the bearings.Steady radial loads result in fully reversed stresses ina rotating shaft which may be increased by stress con-centrations at changes in shaft cross section. Theradial loads in a volute casing increase at rates of flowboth higher and lower than BEP. Radial loads in circu-lar volute or similar styles are minimum at low rates offlow, and increase with increasing rate of flow. It is themanufacturer’s responsibility to define rate of flow lim-its, beyond which, the shaft stress values exceed thedesign fatigue stress limits of the shaft material.

9.6.3.3.8 Horsepower limit

Low specific speed pumps may have horsepowercurves that increase with increasing rate of flow,whereas high specific speed pumps have horsepowercurves that increase with decreasing rate of flow. (SeeANSI/HI 1.1-1.2, Centrifugal Pumps for Nomenclatureand Definitions, Section 1.1.4.1, for a discussion ofspecific speed). The torsional stresses produced bythe higher horsepower requirements may limit theAOR. Each manufacturer establishes limits that pro-vide an adequate torsional stress safety factor.

9.6.3.3.9 Liquid velocity in casing throat

The highest velocity in a pump usually occurs at theentrance to the discharge nozzle. In some designs thevelocity head at high rates of flow may constitute mostof the total discharge head. In such cases, the statichead may drop below the vapor pressure resulting incavitation in the nozzle. In such cases the manufac-turer will limit the maximum flow to avoid cavitationdamage.

9.6.3.3.10 Thrust reversal on impeller

Momentum change, as an axially directed suction flowis turned to a more radial direction in the impeller, pro-duces a thrust force away from the suction. This forceincreases approximately as the square of the rate offlow. If the hydraulic pressure induced axial force onthe impeller is toward the suction, the momentumchange force may exceed the pressure force at higherrates of flow, resulting in thrust reversal. If the thrustbearings are not designed to absorb this thrust rever-sal, the manufacturer will limit the maximum allowablerate of flow.

9.6.3.3.11 NPSHA margin

When pump operation may occur over a wide range ofrates of flow the NPSHA may limit the rate of flow. Fig-ure 9.6.3.1 illustrates a typical relationship betweenNPSHA and NPSHR.

NPSHR VS NPSHA

RATE OF FLOW

NPSHR

NPSHA

NP

SH

Figure 9.6.3.1



4

This limitation is application specific. For more infor-mation on this subject see ANSI/HI 9.6.1-1998, Cen-trifugal and Vertical Pumps for NPSH Margin.

9.6.3.3.12 Head rate of flow curve

Centrifugal Pumps: Some centrifugal pump head rateof flow curves exhibit a characteristic commonlyreferred to as “droop.” A drooping head rate of flowcurve is one for which the zero rate of flow head (shutoff head) is lower than the maximum head on the TotalHead curve. This phenomenon often occurs in low tomedium specific speed pumps which have beendesigned to optimize efficiency. Droop does notpresent an application problem unless one or more ofthe following conditions exist:

a) The static system head is greater than the pumpshut-off head. (The system head curve should notcross the pump curve at two different rates offlow.)

b) The pump is operated in parallel with one or moreother pumps.

c) A continuously rising curve is required for controlpurposes. For example this would occur in a sys-tem that operates with pressure control.

Applying pumps with drooping head curves in theseconditions may cause the pump either to be pushed

back to shutoff, or to hunt between two operatingpoints. Neither condition is desirable. In such casesthe AOR may require further limitation, and/or appro-priate system controls may be implemented, to pre-vent operation at rates of flow less than thatcorresponding to the maximum pump total head. In theabsence of any of the above conditions, pumps withdrooping head curves can perform as well as pumpswith continually rising curves.

Vertical Pumps: High specific speed pumps mayexhibit a “dip” in the head rate of flow curve. To the leftof the dip the head increases steadily with decreasedrate of flow, to the right of the dip the head decreasessteadily with increased rate of flow. Figure 9.6.3.2 illus-trates a head rate of flow curve exhibiting dip.

Continuous operation in the dip region should alwaysbe avoided due to possibly damaging vibration andnoise. In addition, for pumps with specific speedsabove 7000 Metric, (6000 US units), continuous oper-ation must be avoided to the left of the dip region. Ifthe system curve crosses the pump curve in two ormore places, the pump should not be started against aclosed discharge valve. In such cases the pump maynot be able to pass beyond the first point of intersec-tion with the system head curve.

The existence of a dip in the head rate of flow curve ofa pump is not detrimental to use of the pump to theright of the dip region.

Figure 9.6.3.2

DIP RANGE

RATE OF FLOW

VERTICAL PUMP TOTAL HEAD CURVE

TOTA

L H

EA

D



5

9.6.3.3.13 Suction recirculation

Suction recirculation is a condition in which the flow inthe inlet area of an impeller separates from the vanesand forms recirculating eddies. These eddies can pro-duce large forces on the impeller. Experience hasshown that the likelihood of suction recirculation occur-ring is related to suction energy. Suction Energy isdefined as the velocity in a pump suction, squared,times the rate of flow of the pump, times the specificgravity of the liquid pumped. Anything that increasesthe velocity in the pump suction, the rate of flow of thepump or the specific gravity, increases the suctionenergy of the pump. For simplicity we modify this defi-nition as follows:

Suction Energy = D × n × S

Where:

D = Pump Suction Nozzle Size

n = Pump speed in rpm

S = Suction Specific Speed

S = n Q0.5 / NPSHR0.75

The suction nozzle size is used because it approxi-mates the impeller eye diameter and ties to the rate offlow of the pump, the speed ties directly to the inlet tipspeed of the impeller and relative inlet velocities, andthe Suction Specific Speed also has rpm and rate offlow in it. The NPSHR in the Suction Specific Speedcalculation is appropriate as a measure of suctionenergy because larger impeller eye diameters are nor-mally required for lower NPSHR values whichincreases the impeller tip speed (velocity).

Centrifugal Pumps: Figure 9.6.3.3 provides a defini-tion of high suction energy pumps. Figure 9.6.3.4 pro-vides an estimate of the rate of flow for onset ofrecirculation in high suction energy centrifugal pumps.This estimate is to be considered a rough guide only.Actual values of the onset of recirculation can besomewhat higher or lower depending on the specificimpeller design. A manufacturer will normally use Fig-ure 9.6.3.4 to establish the minimum AOR unless oneof the other factors requires a higher value. A test maybe used to verify reliable operation.

Barrel pumps, such as used for boiler feed and pipe-line services, are excluded from this table due to thetypically large shaft diameters in the impeller eye,

Figure 9.6.3.3A (metric)

0 1000 2000PUMP SPEED - RPM

SUCTION ENERGY

S = 14,501 and above

S = 12,201 to 14,500

S = 10,001 to 12,200

S = 10,000 or less

PU

MP

SU

CT

ION

NO

ZZ

LE S

IZE

- M

ILLI

ME

TE

RS

3000 4000

250

0

500

750

REGION OFHIGH SUCTION

ENERGY

REGION OFLOW SUCTION

ENERGY



6

Figure 9.6.3.3B (US units)

0 1000 2000PUMP SPEED - RPM

SUCTION ENERGY

S = 12,501 and above

S = 10,501 to 12,500

S = 8,501 to 10,500

S = 8,500 or less

PU

MP

SU

CT

ION

NO

ZZ

LE S

IZE

- IN

CH

ES

3000 4000

10

0

20

30

REGION OFHIGH SUCTION

ENERGY

REGION OFLOW SUCTION

ENERGY

NOTES for Figure 9.6.3.3 Metric and US Units

1) For two vane impellers and impeller trims with less than 15 degrees vane overlap, reduce suction nozzlesize in Figure 9.6.3.3 by one or two sizes.

2) Inducers, which are generally beyond the scope of this document, should have the suction nozzle in Fig-ure 9.6.3.3 increased by at least one size.

3) For Axial Split Case (Radial Suction) Pumps, increase suction nozzle size in Figure 9.6.3.3 by one size,except when impeller inlet eye diameter exceeds 80% of pump suction nozzle size. Most split casepumps have inlet eye diameters less than 80%.

4) For higher pump speeds than listed in Figure 9.6.3.3, the suction nozzle sizes should be reduced, withthe reduction being proportional to the increase in speed. For example, reduce the nozzle size by 50% ifthe speed is doubled.



7

Figure 9.6.3.4B (US units)

22

20

18

16

12

14

10

840 6045 6550 7055 75 80

SU

CT

ION

SP

EC

IFIC

SP

EE

D (

X 1

000)

ME

TR

IC U

NIT

S

MINIMUM RATE OF FLOW - PERCENT OF BEP RATE OF FLOWAT MAXIMUM DIAMETER IMPELLER

MINIMUM RATE OF FLOW TO AVOID SUCTIONRECIRCULATION FOR HIGH SUCTION ENERGY PUMPS

19

17

15

13

11

9

740 6045 6550 7055 75 80

SU

CT

ION

SP

EC

IFIC

SP

EE

D (

X 1

000)

US

UN

ITS

MINIMUM RATE OF FLOW - PERCENT OF BEP RATE OF FLOWAT MAXIMUM DIAMETER IMPELLER

MINIMUM RATE OF FLOW TO AVOID SUCTIONRECIRCULATION FOR HIGH SUCTION ENERGY PUMPS

Figure 9.6.3.4A (metric)



8

which distorts the relationship between the impellereye diameter and the suction nozzle size.

Vertical Turbine Pumps: For vertical turbine pumpsthe AOR may be limited by impeller inlet tip speed.These limits are due to hydraulic considerations. Table1 provides AOR guidelines for vertical turbine pumps.

Large Boiler Feed Pumps: In many cases, pumps willoperate satisfactorily at flows below the onset of suc-tion and discharge recirculation. Therefore, shouldlower operating flows be necessary or required to con-trol costs of auxiliary systems, consult the OEM for aprecise definition of pump minimum rate of flow.

Table 9.6.3.1

Impeller Inlet Tip SpeedAOR

% BEPm/sec ft/sec

≤ 21 ≤ 70 25 to 115

21.1–23.9 71–78 55 to 115

24.0–26.0 79–85 80 to 115


HI Pumps – Allowable Operating Region Index — 1997

9

Appendix A

Index

This appendix is not part of this standard, but is presented to help the user in considering factors beyond thisstandard.

Note: an f. indicates a figure, and a t. indicates a table.

Allowable operating region, 1centrifugal pumps, 5, 5f., 6f., 7f.factors affecting, 1large boiler feed pumps, 8vertical turbine pumps, 8, 8t.

AOR See Allowable operating region

Bearing life, 2BEP See Best efficiency pointBest efficiency point, 1

Head rate of flow curvecentrifugal pumps, 4vertical pumps, 4, 4f.

Horsepower limit, 3

Internal mechanical contact, 2

Liquid velocity in casing throat, 3

Net positive suction head allowable, 3Net positive suction head requiredNoise, 2NPSHA margin, 3, 3f.NPSHA See Net positive suction head allowableNPSHR See Net positive suction head required

POR See Preferred operating regionPreferred operating region, 1

vertical pumps, 1

Shaft fatigue failure, 3Shaft seal life, 2Suction energy, 5Suction recirculation, 5

centrifugal pumps, 5, 5f., 6f., 7f.large boiler feed pumps, 8vertical turbine pumps, 8, 8t.

Suction specific speed, 5

Temperature rise, 2Thrust reversal on impeller, 3

Vibration, 2


M120

Documents

ANSI HI 9.6.3-1997