ANSI/HI 9.6.3-1997
American National Standard for
Centrifugal and
Vertical Pumps
ANSI/HI 9.6.3-1997
for Allowable Operating
Region
9 Sylvan Way
Parsippany, New Jersey
07054-3802
www.pumps.org
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Copyright © 2000 By Hydraulic Institute, All Rights Reserved.
ANSI/HI 9.6.3-1997
American National Standard for
Centrifugal and Vertical Pumps
for Allowable Operating Region
Secretariat
Hydraulic Institute
www.pumps.org
Approved August 20, 1997
American National Standards Institute, Inc.
Recycled
paper
Copyright © 2000 By Hydraulic Institute, All Rights Reserved.
of an American National Standard requires verification by ANSI that the
American Approval
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 ANSI 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 Institute does not develop standards and will in no
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person shall have the right or authority to issue an interpretation of an American
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CAUTION NOTICE: This American National Standard may be revised or withdrawn at
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Published By
Hydraulic Institute
9 Sylvan Way, Parsippany, NJ 07054-3802
www.pumps.org
Copyright © 1997 by Hydraulic Institute
All rights reserved.
No part of this publication may be reproduced in any form,
in an electronic retrieval system or otherwise, without prior
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Printed in the United States of America
ISBN 1-880952-24-6
Copyright © 2000 By Hydraulic Institute, All Rights Reserved.
Contents
Page
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
iii
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This page intentionally blank.
Copyright © 2000 By Hydraulic Institute, All Rights Reserved.
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 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 business 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 Institute 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 Institute Standards is completely voluntary. Existence of
Hydraulic Institute 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 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 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
Institute 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 the contents of an Institute publication or an answer
provided by the Institute 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.
v
Copyright © 2000 By Hydraulic Institute, All Rights Reserved.
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.
Scope
This standard applies to centrifugal and vertical pump types. It describes the
effects of operating a centrifugal or vertical pump at rates of flow that are above or
below 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 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 standardization 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.
Agrico Chemical Corporation
American Society of Heating,
Refrigerating & Air Conditioning
Engineers
American Society of Mechanical
Engineers
Amoco Oil Company
Black & Veatch
BP America
Brown & Caldwell
Camp Dresser & McKee, Inc.
CH2M Hill
De Wanti & Stowell
Dow Chemical
DuPont Engineering
Durametallic Corporation
Electric Power Research Institute
Fleet Tech. Supt. Center
Florida Power Corporation
Foth & Van Dyke
GT Exporters
Hydraulic Institute
Institute of Paper Science & Tech.
John Carollo Engineers
John Crane, Inc.
Malcolm Pirnie, Inc.
Marine Machinery Assoc.
Material Tech. Inst. of ChemPro
Montana State University
Montgomery Watson
Mobil Technology Co.
Naval Surface Warfare Center
OWP&P Consultants
Oxy Chemical
Raytheon Engineers & Constructors
Star Enterprises
State of California, Dept. of Water
Stone & Webster
Summers Engineering
Systicon, Inc.
Union Carbide Corporation
US Bureau Of Reclamation
vi
Copyright © 2000 By Hydraulic Institute, All Rights Reserved.
HI Pumps – Allowable Operating Region — 1997
9.6.3 Allowable operating region
9.6.3.1
HI Pumps – Allowable Operating Region
range the calculated minimum bearing life will allow
two years of service.
Preferred operating region
This standard describes the effects of operating a centrifugal pump at rates of flow that are above or below
the rate of flow at the pump’s best efficiency point
(BEP). These effects influence the life of pump components and therefore an understanding of them is
essential to all concerned. Design characteristics for
both performance and service life are optimized
around a rate of flow designated as the Best Efficiency
Point (BEP). At BEP the hydraulic efficiency is maximum, and the liquid enters the impeller vanes, casing
diffuser (discharge nozzle) or vaned diffuser in a
shockless manner. Flow through the impeller and diffuser vanes (if so equipped) is uniform and free of separation, and is well controlled. The flow remains well
controlled within a range of rates of flow designated as
the Preferred Operating Region (POR). Within this
region the service life of the pump will not be significantly affected by hydraulic loads, vibration, or flow
separation.
Centrifugal Pumps: The POR for most centrifugal
pumps is between 70% and 120% of BEP. For smaller
pumps less than 4 kw (5 HP) the manufacturer may
recommend a wider POR.
The service life of any piece of mechanical equipment
is dependent on a large number of factors. This discussion deals only with those factors related to operating rates of flow and pump design. Other factors such
as proper equipment selection, installation, maintenance, and operation are not addressed here.
It is also assumed that the pumped liquid is a nonviscous, noncorrosive, pure liquid with no vapor, gas,
suspended solids or abrasives. For other liquids the
general principles contained herein apply with quantitative modifications. Certain special liquid mixtures
may have other characteristics which affect the AOR.
For example, the minimum rate of flow when pumping
a liquid which contains entrained air may be determined by air separation at the eye of the impeller.
When a manufacturer’s recommendations deviate significantly from these guidelines, or a concern exists
regarding the ability of the pump to operate reliably at
the specified rate of flow, a factory test should be
specified. Characteristics that should be monitored
during the test include one or more of the following as
appropriate:
– stability of rate of flow being pumped;
Vertical Pumps: Well controlled flow in higher specific
speed pumps occurs in a narrower flow range. Thus
the POR for vertical pumps is:
– bearing housing vibration;
– shaft vibration;
Specific Speed
POR
Metric
US Unit
≤ 5200
≤ 4500
Between 70% & 120% of BEP
> 5200
> 4500
Between 80% & 115% of BEP
9.6.3.2
– motor vibration;
– bearing temperature;
– noise.
Allowable operating region
A wider operating range is termed the Allowable Operating Region (AOR). The AOR is that range of rates of
flow recommended by the pump manufacturer over
which the service life of a pump is not seriously compromised. Minimum bearing life will be reduced and
noise, vibration, and component stresses will be
increased when a pump is operated outside its POR.
As a result, service life within the AOR may be lower
than within the POR. It should be recognized that
while the calculated minimum bearing life may vary
significantly over the AOR, at any point within this
Acceptance criteria for the above shall be agreed to by
the producer and purchaser at the time the test is
ordered.
9.6.3.3
Factors affecting AOR
Following is a list of the factors that a pump manufacturer considers when establishing the AOR. Within the
AOR the manufacturer has determined that none of
the factors exceeds limits that will severely impact the
service life of the pump. The factor that determines the
upper or lower limits of the AOR will normally vary with
pump type and specific design, and may not be evident from the manufacturer’s literature. This list, and
1
Copyright © 2000 By Hydraulic Institute, All Rights Reserved.
HI Pumps – Allowable Operating Region — 1997
– bearing life;
have a shorter calculated bearing life. Vertical diffuser
pumps and pumps with hydrodynamic bearings do not
normally have a calculated bearing life with respect to
rate of flow, but rate of flow limitations may be considered in calculating bearing whirl and maximum load
rate of flow.
– shaft seal life;
9.6.3.3.3 Shaft seal life
– vibration;
– horsepower limit;
Excessive shaft deflection at the faces of a mechanical
seal will reduce the seal life. Most process pump manufacturers limit the AOR to operating conditions where
the shaft deflection at the seal faces is 0.05mm (0.002
in.) or less for pumps with rolling element bearings.
Since most seal designs and all compression packed
pumps permit greater deflections, the continuous rate
of flow limits (both maximum and minimum) are application specific.
– liquid velocity in casing throat;
9.6.3.3.4 Vibration
– thrust reversal on impeller;
The HI Standards specify the maximum allowable
vibration for Centrifugal and Vertical pumps. These
pumps typically exhibit a minimum vibration near the
Best Efficiency Point, with increases in vibration at
higher and lower rates of flow. Vibration levels exceeding the allowable limits are one criterion for establishing the AOR.
the following discussion of each, is provided as an aid
in understanding the acceptable operating limits:
– temperature rise;
– noise;
– internal mechanical contact;
– shaft fatigue failure;
– NPSHA margin;
– slope of the head–rate-of-flow curve;
– suction recirculation.
It should be noted that the design characteristics of
smaller pumps may not be determined by load and
deflection criteria, but by manufacturing and standard
hardware considerations. These scale factors often
result in smaller pumps being more robust than larger
pumps with respect to the imposed loads. A manufacturer often includes these effects in determining the
AOR.
9.6.3.3.1 Temperature rise
ANSI/HI 1.3, Centrifugal Pumps for Design and Application, Section 1.3.3.2.4, provides a recommended
practice for calculating the minimum thermal rate of
flow. This rate of flow is dependent on the specific
heat, the vapor pressure-temperature relationship of
the pumped fluid, as well as the NPSHA/NPSHR ratio.
Consequently the minimum thermal rate of flow is
application specific.
9.6.3.3.2 Bearing life
Manufacturers will limit the AOR for pumps designed
to operate continuously to operating conditions where
the bearing life is equal to or greater than 17,500
hours. Pumps designed for intermittent service may
9.6.3.3.5 Noise
A certain amount of noise is expected from any pump.
Pumps with higher energy levels usually operate with
higher noise levels. It is often found that, at higher and
lower rates of flow, and lower NPSH margins, the
noise changes from a sound characterized as sand
sliding down a chute, to one of gravel or rocks. The
change in sound level is often not distinguishable on a
sound level meter, but the change in sound characteristic is detectable by the human ear. Gravel and rock
sounds are usually caused by cavitation in the pump
suction and may cause mechanical damage and can
limit the AOR. A noise test may be used to help evaluate the AOR.
9.6.3.3.6 Internal mechanical contact
Hydraulic loads originating in the impeller or casing
produce deflections in mechanical components. The
loads may be steady or varying, but usually change as
the operating rate of flow changes. As loads increase,
deflections may become so large as to result in contact between rotating and stationary parts. This may
not be harmful if the parts are compatible (i.e., nongalling combinations of impeller and casing rings). Each
2
Copyright © 2000 By Hydraulic Institute, All Rights Reserved.
HI Pumps – Allowable Operating Region — 1997
manufacturer evaluates their design and operating
experience to determine if operating limits should be
established.
9.6.3.3.7 Shaft fatigue failure
Hydraulic loads originating in the impeller or casing
are transmitted through the shaft to the bearings.
Steady radial loads result in fully reversed stresses in
a rotating shaft which may be increased by stress concentrations at changes in shaft cross section. The
radial loads in a volute casing increase at rates of flow
both higher and lower than BEP. Radial loads in circular volute or similar styles are minimum at low rates of
flow, and increase with increasing rate of flow. It is the
manufacturer’s responsibility to define rate of flow limits, beyond which, the shaft stress values exceed the
design fatigue stress limits of the shaft material.
9.6.3.3.8 Horsepower limit
Low specific speed pumps may have horsepower
curves that increase with increasing rate of flow,
whereas high specific speed pumps have horsepower
curves that increase with decreasing rate of flow. (See
ANSI/HI 1.1-1.2, Centrifugal Pumps for Nomenclature
and Definitions, Section 1.1.4.1, for a discussion of
specific speed). The torsional stresses produced by
the higher horsepower requirements may limit the
AOR. Each manufacturer establishes limits that provide 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 the
entrance to the discharge nozzle. In some designs the
velocity head at high rates of flow may constitute most
of the total discharge head. In such cases, the static
head may drop below the vapor pressure resulting in
cavitation in the nozzle. In such cases the manufacturer will limit the maximum flow to avoid cavitation
damage.
9.6.3.3.10
Thrust reversal on impeller
Momentum change, as an axially directed suction flow
is turned to a more radial direction in the impeller, produces a thrust force away from the suction. This force
increases approximately as the square of the rate of
flow. If the hydraulic pressure induced axial force on
the impeller is toward the suction, the momentum
change force may exceed the pressure force at higher
rates of flow, resulting in thrust reversal. If the thrust
bearings are not designed to absorb this thrust reversal, the manufacturer will limit the maximum allowable
rate of flow.
9.6.3.3.11
NPSHA margin
When pump operation may occur over a wide range of
rates of flow the NPSHA may limit the rate of flow. Figure 9.6.3.1 illustrates a typical relationship between
NPSHA and NPSHR.
NPSHR VS NPSHA
NPSH
NPSHR
NPSHA
RATE OF FLOW
Figure 9.6.3.1
3
Copyright © 2000 By Hydraulic Institute, All Rights Reserved.
HI Pumps – Allowable Operating Region — 1997
This limitation is application specific. For more information on this subject see ANSI/HI 9.6.1-1998, Centrifugal and Vertical Pumps for NPSH Margin.
9.6.3.3.12
Head rate of flow curve
Centrifugal Pumps: Some centrifugal pump head rate
of flow curves exhibit a characteristic commonly
referred to as “droop.” A drooping head rate of flow
curve is one for which the zero rate of flow head (shut
off head) is lower than the maximum head on the Total
Head curve. This phenomenon often occurs in low to
medium specific speed pumps which have been
designed to optimize efficiency. Droop does not
present an application problem unless one or more of
the following conditions exist:
a) The static system head is greater than the pump
shut-off head. (The system head curve should not
cross the pump curve at two different rates of
flow.)
b) The pump is operated in parallel with one or more
other pumps.
c) A continuously rising curve is required for control
purposes. For example this would occur in a system that operates with pressure control.
Applying pumps with drooping head curves in these
conditions may cause the pump either to be pushed
back to shutoff, or to hunt between two operating
points. Neither condition is desirable. In such cases
the AOR may require further limitation, and/or appropriate system controls may be implemented, to prevent operation at rates of flow less than that
corresponding to the maximum pump total head. In the
absence of any of the above conditions, pumps with
drooping head curves can perform as well as pumps
with continually rising curves.
Vertical Pumps: High specific speed pumps may
exhibit a “dip” in the head rate of flow curve. To the left
of the dip the head increases steadily with decreased
rate of flow, to the right of the dip the head decreases
steadily with increased rate of flow. Figure 9.6.3.2 illustrates a head rate of flow curve exhibiting dip.
Continuous operation in the dip region should always
be avoided due to possibly damaging vibration and
noise. In addition, for pumps with specific speeds
above 7000 Metric, (6000 US units), continuous operation must be avoided to the left of the dip region. If
the system curve crosses the pump curve in two or
more places, the pump should not be started against a
closed discharge valve. In such cases the pump may
not be able to pass beyond the first point of intersection with the system head curve.
The existence of a dip in the head rate of flow curve of
a pump is not detrimental to use of the pump to the
right of the dip region.
TOTAL HEAD
VERTICAL PUMP TOTAL HEAD CURVE
DIP RANGE
RATE OF FLOW
Figure 9.6.3.2
4
Copyright © 2000 By Hydraulic Institute, All Rights Reserved.
HI Pumps – Allowable Operating Region — 1997
9.6.3.3.13
Suction recirculation
Suction recirculation is a condition in which the flow in
the inlet area of an impeller separates from the vanes
and forms recirculating eddies. These eddies can produce large forces on the impeller. Experience has
shown that the likelihood of suction recirculation occurring is related to suction energy. Suction Energy is
defined as the velocity in a pump suction, squared,
times the rate of flow of the pump, times the specific
gravity of the liquid pumped. Anything that increases
the velocity in the pump suction, the rate of flow of the
pump or the specific gravity, increases the suction
energy of the pump. For simplicity we modify this definition 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 approximates the impeller eye diameter and ties to the rate of
flow of the pump, the speed ties directly to the inlet tip
speed of the impeller and relative inlet velocities, and
the Suction Specific Speed also has rpm and rate of
flow in it. The NPSHR in the Suction Specific Speed
calculation is appropriate as a measure of suction
energy because larger impeller eye diameters are normally required for lower NPSHR values which
increases the impeller tip speed (velocity).
Centrifugal Pumps: Figure 9.6.3.3 provides a definition of high suction energy pumps. Figure 9.6.3.4 provides an estimate of the rate of flow for onset of
recirculation in high suction energy centrifugal pumps.
This estimate is to be considered a rough guide only.
Actual values of the onset of recirculation can be
somewhat higher or lower depending on the specific
impeller design. A manufacturer will normally use Figure 9.6.3.4 to establish the minimum AOR unless one
of the other factors requires a higher value. A test may
be used to verify reliable operation.
Barrel pumps, such as used for boiler feed and pipeline services, are excluded from this table due to the
typically large shaft diameters in the impeller eye,
PUMP SUCTION NOZZLE SIZE - MILLIMETERS
SUCTION ENERGY
750
500
REGION OF
HIGH SUCTION
ENERGY
S
=
10
,00
0o
r le
ss
10,
001
S=
to 1
2,20
12,
0
201
to 1
S=
4
,500
14,
5 01
and
abov
e
S=
250
REGION OF
LOW SUCTION
ENERGY
0
0
1000
2000
3000
4000
PUMP SPEED - RPM
Figure 9.6.3.3A (metric)
5
Copyright © 2000 By Hydraulic Institute, All Rights Reserved.
HI Pumps – Allowable Operating Region — 1997
SUCTION ENERGY
PUMP SUCTION NOZZLE SIZE - INCHES
30
20
REGION OF
HIGH SUCTION
ENERGY
S
10
REGION OF
LOW SUCTION
ENERGY
=
8,5
00
or
les
S=
s
8,5
01
to 1
S=
0,50
10,
0
501
S=
to 1
2,50
12,
0
501
and
abov
e
0
0
1000
2000
3000
4000
PUMP SPEED - RPM
Figure 9.6.3.3B (US units)
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 nozzle
size 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 Figure 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 case
pumps 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, with
the reduction being proportional to the increase in speed. For example, reduce the nozzle size by 50% if
the speed is doubled.
6
Copyright © 2000 By Hydraulic Institute, All Rights Reserved.
HI Pumps – Allowable Operating Region — 1997
SUCTION SPECIFIC SPEED (X 1000) METRIC UNITS
MINIMUM RATE OF FLOW TO AVOID SUCTION
RECIRCULATION FOR HIGH SUCTION ENERGY PUMPS
22
20
18
16
14
12
10
8
40
45
50
55
60
65
70
75
80
MINIMUM RATE OF FLOW - PERCENT OF BEP RATE OF FLOW
AT MAXIMUM DIAMETER IMPELLER
Figure 9.6.3.4A (metric)
MINIMUM RATE OF FLOW TO AVOID SUCTION
RECIRCULATION FOR HIGH SUCTION ENERGY PUMPS
SUCTION SPECIFIC SPEED (X 1000) US UNITS
19
17
15
13
11
9
7
40
45
50
55
60
65
70
75
80
MINIMUM RATE OF FLOW - PERCENT OF BEP RATE OF FLOW
AT MAXIMUM DIAMETER IMPELLER
Figure 9.6.3.4B (US units)
7
Copyright © 2000 By Hydraulic Institute, All Rights Reserved.
HI Pumps – Allowable Operating Region — 1997
which distorts the relationship between the impeller
eye diameter and the suction nozzle size.
Vertical Turbine Pumps: For vertical turbine pumps
the AOR may be limited by impeller inlet tip speed.
These limits are due to hydraulic considerations. Table
1 provides AOR guidelines for vertical turbine pumps.
Large Boiler Feed Pumps: In many cases, pumps will
operate satisfactorily at flows below the onset of suction and discharge recirculation. Therefore, should
lower operating flows be necessary or required to control costs of auxiliary systems, consult the OEM for a
precise definition of pump minimum rate of flow.
Table 9.6.3.1
Impeller Inlet Tip Speed
m/sec
ft/sec
AOR
% BEP
≤ 21
≤ 70
25 to 115
21.1–23.9
71–78
55 to 115
24.0–26.0
79–85
80 to 115
8
Copyright © 2000 By Hydraulic Institute, All Rights Reserved.
HI Pumps – Allowable Operating Region Index — 1997
Appendix A
Index
This appendix is not part of this standard, but is presented to help the user in considering factors beyond this
standard.
Note: an f. indicates a figure, and a t. indicates a table.
Allowable operating region, 1
centrifugal pumps, 5, 5f., 6f., 7f.
factors affecting, 1
large boiler feed pumps, 8
vertical turbine pumps, 8, 8t.
AOR See Allowable operating region
Bearing life, 2
BEP See Best efficiency point
Best efficiency point, 1
Head rate of flow curve
centrifugal pumps, 4
vertical pumps, 4, 4f.
Horsepower limit, 3
POR See Preferred operating region
Preferred operating region, 1
vertical pumps, 1
Shaft fatigue failure, 3
Shaft seal life, 2
Suction energy, 5
Suction recirculation, 5
centrifugal pumps, 5, 5f., 6f., 7f.
large boiler feed pumps, 8
vertical turbine pumps, 8, 8t.
Suction specific speed, 5
Temperature rise, 2
Thrust reversal on impeller, 3
Internal mechanical contact, 2
Vibration, 2
Liquid velocity in casing throat, 3
Net positive suction head allowable, 3
Net positive suction head required
Noise, 2
NPSHA margin, 3, 3f.
NPSHA See Net positive suction head allowable
NPSHR See Net positive suction head required
9
Copyright © 2000 By Hydraulic Institute, All Rights Reserved.
M120
Copyright © 2000 By Hydraulic Institute, All Rights Reserved.