ISO 21630:2007

Pumps — Testing — Submersible mixers for wastewater and similar applications

ISO 21630:2007 prescribes acceptance test methods for submersible mixers used for mixing in wastewater and other applications where at least one system component is a liquid. "Submersible mixer" is taken to mean a fully submersible aggregate consisting of a drive unit and an axial flow type impeller, and optional parts, such as shrouds, supporting the basic functions. "Liquid" is taken to mean a body without capacity to accommodate shear stresses when at rest. This includes suspensions and dispersions (liquid/solid, gas/liquid and gas/liquid/solid), and non-Newtonian liquids, provided that a possible small yield stress does not prevent the liquid from flowing when agitated.

Pompes — Essais — Mélangeurs immergés pour eaux usées et applications similaires

General Information

• Status: Published
• Publication Date: 12-Aug-2007
• ICS: 23.080 - Pumps
• Technical Committee: ISO/TC 115/SC 2 - Methods of measurement and testing
• Drafting Committee: ISO/TC 115/SC 2 - Methods of measurement and testing
• Current Stage: 9060 - Close of review
• Start Date: 02-Sep-2026

Relations

• Child: ISO 15958:2019 - Fertilizers — Extraction of water soluble phosphorus
• Effective Date: 06-Jun-2022

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 21630
First edition
2007-08-15

Pumps — Testing — Submersible mixers
for wastewater and similar applications
Pompes — Essais — Mélangeurs immergés pour eaux usées et
applications similaires




Reference number
ISO 21630:2007(E)
©
ISO 2007

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ISO 21630:2007(E)
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ISO 21630:2007(E)
Contents Page
Foreword. iv
Introduction . v
1 Scope. 1
2 Terms and definitions. 1
3 Symbols and abbreviated terms . 3
4 Guarantees. 4
4.1 Subjects of guarantees . 4
4.2 Conditions of guarantees . 5
5 Execution of tests. 5
5.1 Subjects of tests . 5
5.2 Organization of tests . 6
5.3 Test arrangements. 8
5.4 Test conditions . 8
6 Analysis of test results. 11
6.1 Translation of the test results to the guarantee conditions. 11
6.2 Measurement uncertainties. 12
6.3 Values of tolerance factors. 13
6.4 Verification of guarantees. 14
7 Measurement of thrust . 15
7.1 Flow conditions of mixer thrust measurement. 15
7.2 Mixer thrust measurement method. 18
7.3 Uncertainty of measurement . 18
8 Measurement of mixer electric power uptake. 19
Annex A (informative) Checklist . 20
Bibliography . 21

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ISO 21630:2007(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 21630 was prepared by Technical Committee ISO/TC 115, Pumps, Subcommittee SC 2, Methods of
measurement and testing.

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ISO 21630:2007(E)
Introduction
This International Standard prescribes acceptance test methods for submersible mixers for wastewater and
other applications. It is intended for performance measurements relevant to submersible mixers bearing in
mind the similarities to, and crucial differences from, submersible pumps. Hence head (pressure) and flow rate
measurements are not included. The basic output performance parameter is the thrust. As continuous
operation is commonplace, electric power consumption is important for the Life Cycle Cost, and is put forward
as an important parameter. It is acknowledged that the present International Standard draws heavily on
ISO 9906:1999 in the generalities.
The major objectives of this International Standard are to
⎯ increase uniformity/compatibility in equipment performance characterization, enabling a comparison of
mixers,
⎯ simplify communication between customer and supplier and protect customers,
⎯ reduce the need for documentation,
⎯ increase quality and efficiency in both machinery and process.


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INTERNATIONAL STANDARD ISO 21630:2007(E)

Pumps — Testing — Submersible mixers for wastewater and
similar applications
1 Scope
This International Standard prescribes acceptance test methods for submersible mixers (hereafter “SM” or
“mixer”) used for mixing in wastewater and other applications where at least one system component is a liquid.
“Submersible mixer” is taken to mean a fully submersible aggregate consisting of a drive unit and an axial flow
type impeller, and optional parts, such as shrouds, supporting the basic functions.
“Liquid” is taken to mean a body without capacity to accommodate shear stresses when at rest. This includes
suspensions and dispersions (liquid/solid, gas/liquid and gas/liquid/solid), and non-Newtonian liquids, provided
that a possible small yield stress does not prevent the liquid from flowing when agitated.
2 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
2.1
thrust-to-power ratio
ratio of mixer thrust force to mixer power consumption
R = F / P
FP 1
NOTE 1 The ratio of minimum required mixing system power dissipation to mixer power consumption is an (end-user
oriented) system efficiency. To understand the importance of the thrust-to-power ratio, consider the case of an SM
generating a longitudinal flow velocity u in a recirculation channel such as a wastewater oxidation ditch. This is in fact a
common application of the SM, and the following argument is in principle possible to generalize to other applications.
The momentum loss of the flow over one circulation equals the rate of momentum provided by the SM at quasi-steady
state. This is given by the mixer thrust F. The power dissipated as a result of this momentum loss is P = F u, and this is the
minimum required mixing system power to maintain the velocity u. Hence, the system efficiency is P / P = F u / P .
1 1
It is possible to isolate the mixer properties from the system requirement in this expression, and this leads to the thrust-to-
power ratio, R , as the most relevant efficiency-related parameter of the SM. It should be noted that it is dimensional, and
FP
hence it depends on the impeller diameter and speed, not only on the impeller geometry. Other considerations than
energetic efficiency of generation of longitudinal flow provide for the multitude of impeller diameters and speeds available
in practice.
NOTE 2 An impeller efficiency, defined as the ratio of power of axial motion of the impeller discharge to the electric
power uptake of the mixer, can be defined. The definition draws on the assumption that the approaching velocity, u, is
small enough to have negligible influence on the mixer impeller characteristics. The hydraulic discharge power P = p Q
h
can be expressed in thrust using the relations
2
p = F / A and F = 2 ρ Q / A
which are approximately valid for the mixer test established herein. The conventional area of the vena contracta A / 2 is
2
used, as this discharge section best fulfils the flat velocity profile requirement. With A = π D / 4, one obtains
1/2 3/2 1/2
P = (F / A) (A F / 2 ρ) = F / [D (π ρ / 2) ]
h
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ISO 21630:2007(E)
Hence the impeller efficiency can be written
3/2 1/2
η = F / [(π ρ / 2) D P ]
1
It can be noted that, often correct to within 1 %, the efficiency is conventionally given as (assuming SI units [F] = Newton,
[P ] = Watt, [D] = meter, and clean cold water as defined in 5.4.5.2)
1
3/2
η = F / (40 D P )
1
Although the derivation given here is not based on completely correct assumptions, the approximate expression for the
efficiency may be derived in more rigorous ways.
The value of the impeller efficiency alone is not deemed to be of primary interest because of the dependency of mixer-
system efficiency on the impeller diameter and speed.
2.2
advance ratio
ratio of propeller traversing speed or mean liquid ambient speed to (essentially) tip speed
J = u / nD
2.3
impeller Reynolds number
ratio between inertial and viscous forces prevailing at impeller
1/2
Re = (F / ρ ) / ν
NOTE F is the thrust for the same mixer running at the same speed in clean cold water as defined in 5.4.5.2. Also
note that this is not the same as the blade Reynolds number, nor is it identical, but akin to the impeller Reynolds number
used for dry-installed agitators in the process industries.

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ISO 21630:2007(E)
3 Symbols and abbreviated terms
Table 1 summarizes the symbols in alphabetical order and SI units used.
Table 1 — Alphabetical list of letters used as symbols
Symbol Quantity Unit

2
A Area swept by impeller m
D Diameter of impeller m
e Uncertainty, relative (pure number), %
−1
f Frequency s , Hz
F Thrust N
J Propeller advance ratio (pure number)
L Length of lever m
−1
n Speed of rotation s , Hz
p Pressure Pa
P Power W
3
Q Flow rate m /s
R Thrust-to-power ratio N/W
FP
Re Impeller Reynolds number (pure number)
t Tolerance (pure number), %
T Time s
u Mean velocity in the axial or m/s
longitudinal direction
U Voltage V
x Generic measured entity
Time average of x
η Efficiency (pure number), %
2
ν Kinematic viscosity m /s
3
ρ Density kg/m
σ Standard deviation

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ISO 21630:2007(E)
Table 2 summarizes the subscripts used for the symbols.
Table 2 — Alphabetical list of letters and figures other than above used as subscript
Subscript Meaning
1 electric (power)
G guaranteed
L/L length ratio
h hydraulic (power)
LC load cell related
m measured
M mixer related
FP see R
FP
sp specified
Tr translated
TS time series

4 Guarantees
4.1 Subjects of guarantees
4.1.1 General
Terms used herein such as “guarantee” or “acceptance” should be understood in a technical but not in a legal
sense. The term “guarantee” therefore specifies values for checking purposes determined in the contract, but
does not say anything about the rights or duties arising if these values are not reached or fulfilled. The term
“acceptance” does not have any legal meaning here, either. Therefore, an acceptance test carried out
successfully alone does not represent an “acceptance” in the legal sense.
A procedure for verifying the guarantees is given in 6.4.
4.1.2 Thrust guarantee
One guarantee point shall be defined by a guarantee thrust F .
G
The manufacturer/supplier guarantees that under the standard test conditions established in this document,
the measured thrust will fall in a specified interval surrounding F . Unless otherwise stated, the interval is
G
given by the tolerances stated in Table 6.
4.1.3 Electric power uptake guarantee
One guarantee point shall be defined by a guarantee electric power uptake P .
1G
The manufacturer/supplier guarantees that under the standard test conditions established in this document,
the measured electric power uptake will fall in a specified interval surrounding P . Unless otherwise stated,
1G
the interval is given by the tolerances stated in Table 6.
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ISO 21630:2007(E)
4.1.4 Thrust-to-power ratio guarantee
One guarantee point shall be defined by a guarantee thrust-to-power ratio R . This shall be given by
FP,G
R = F / P .
FP,G G 1G
The manufacturer/supplier guarantees that under the standard test conditions established in this document,
the measured and calculated thrust-to-power ratio will fall in a specified interval surrounding R . Unless
FP,G
otherwise stated, the interval is given by the tolerances stated in Table 6.
4.2 Conditions of guarantees
Unless otherwise agreed, the following conditions shall apply to the guaranteed value.
a) The guarantee point shall apply to clean cold water (see 5.4.5.2).
b) The relationship between the guarantee values under clean cold water conditions and the likely
performance under other liquid conditions shall be agreed in the contract.
c) Guarantees shall apply only to the mixer as tested by the methods and in the test arrangements specified
herein.
d) The relationship between the guarantee values under the conditions of the methods and test
arrangements specified herein and the likely performance under other operating conditions shall be
agreed in the contract.
5 Execution of tests
5.1 Subjects of tests
5.1.1 General
If not otherwise agreed between the manufacturer/supplier and the purchaser, the following shall apply:
⎯ accuracy according to 6.2; and
⎯ tests shall be carried out on the test stand of the manufacturer’s works, or on a test stand engaged by the
manufacturer/supplier.
Any deviations from this shall be agreed between the purchaser and manufacturer/supplier. This should be
done as soon as possible, and should preferably form part of the contract.
Among others, such deviations may be
a) accuracy other than that given in 6.2,
b) tolerance factors other than those given in 6.3,
c) tests in a neutral laboratory.
Annex A shows a checklist of items where agreement between the purchaser and manufacturer/supplier is
recommended.
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ISO 21630:2007(E)
5.1.2 Contractual tests — Fulfilment of the guarantee
The tests are intended to ascertain the performance of the mixer and to compare this with the
manufacturer’s/supplier’s guarantee. The nominated guarantee for any quantity shall be deemed to have been
met if, when tested according to this International Standard, the measured performance falls within the
tolerance specified for the particular quantity.
When a number of identical mixers are to be purchased, the number of mixers to be tested shall be agreed
upon between the purchaser and the manufacturer/supplier.
5.2 Organization of tests
5.2.1 General
Both purchaser and manufacturer/supplier shall be entitled to witness these tests. The test supervisor may
delegate his/her responsibilities under 5.2.4 to the test operator, provided the test operator is sufficiently
trained to handle these responsibilities.
5.2.2 Location of tests
Performance tests should preferably be carried out at the manufacturer’s works, or at another test stand
engaged by the manufacturer/supplier, or at a place to be mutually agreed between the manufacturer/supplier
and the purchaser.
5.2.3 Date of testing
The date of testing shall be mutually agreed by the manufacturer/supplier and the purchaser if the purchaser
by contract requires to witness the test.
5.2.4 Staff
Accurate measurements depend not only on the quality of the measuring instrument used but also on the
ability and skill of the persons operating and reading the measurement devices during the tests. The staff
entrusted with effecting the measurements shall be selected just as carefully as the instruments to be used in
the test.
Specialists with adequate experience in measuring operations in general shall be charged with operating and
reading complicated measuring apparatus. Reading simple measuring devices may be entrusted to such
helpers who (upon prior instructions) can be assumed to effect the readings with proper care and the accuracy
required.
A test supervisor possessing adequate experience in measuring operations shall be mutually appointed.
Normally, when the test is carried at the manufacturer’s works, the test supervisor is a staff member of the
mixer manufacturer.
During the tests all persons charged with effecting the measurements are subordinated to the chief of tests,
who conducts and supervises the measurements, reports on test conditions and the results of the tests and
then drafts the test report. All questions arising in connection with the measurements and their execution are
subject to his/her decision. The parties concerned shall provide all assistance that the chief of tests considers
necessary.
5.2.5 State of mixer
When tests are not carried out in the manufacturer’s works, or at another test stand engaged by the
manufacturer/supplier, both the manufacturer and the installer shall be allowed the opportunity to make
preliminary adjustments.
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ISO 21630:2007(E)
5.2.6 Test program
The program and procedure to be followed in the test shall be prepared by the test supervisor and submitted
to both manufacturer/supplier and purchaser in ample time for consideration and agreement.
Only the guaranteed operational data (see 4.1) shall form the basis of the test; other data determined by
measurement during the tests shall have merely an indicative (informative) function and it shall be so stated if
they are included in the program.
5.2.7 Testing equipment
When deciding on the measuring procedure, the measuring, recording and data handling apparatus shall be
specified at the same time. The test supervisor shall be responsible for checking the correct installation of the
apparatus and its proper functioning.
All of the measuring apparatus shall be covered by reports showing, by calibration or by comparison with
other ISO or IEC standards, that it complies with the requirement of 6.2.3. These reports shall be presented if
required. Guidance for a suitable period between calibrations of test instruments is given in Annex E of
ISO 9906:1999. For test instruments other than those given there, e.g. force measurement instruments, a
period of at most one year between calibrations is recommended.
5.2.8 Records
All test records and record charts shall be initialled by the test supervisor and by the representatives of both
the manufacturer/supplier and purchaser, if present, each of whom shall be provided with a copy of all records
and charts.
The evaluation of the test results shall be made as far as possible while the tests are in progress and, in any
case, before the installation and instrumentation are dismantled in order that suspect measurements can be
repeated without delay.
5.2.9 Test report
If the purchaser has requested a test report, then, after scrutiny, the test results shall be summarized in a
report which is signed by the test supervisor or test operator alone, or together, by him/her and
representatives of the manufacturer/supplier and of the purchaser. All parties specified in the contract shall
receive a copy of the report.
The test report should contain the following information:
a) place and date of acceptance test;
b) manufacturer’s name, type of mixer, and serial number;
c) impeller/propeller diameter, blade angle or other hydraulic end identifications;
d) guaranteed characteristics, operational conditions during the acceptance test;
e) specification of the mixer’s driver;
f) sketch of test arrangement, description of the test procedure and the measuring apparatus including
calibration data;
g) readings;
h) evaluation and analysis of test results;
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ISO 21630:2007(E)
i) conclusions:
⎯ comparison of the test results and the guaranteed quantities;
⎯ determination of action taken in connection with any special agreements that were made;
⎯ recommendation on whether the mixer can be accepted or should be rejected and under what
conditions (if the guarantees are not fully satisfied the final decision whether the mixer can be
accepted or not is up to the purchaser);
⎯ statements arising out of action taken in connection with any special agreements that were made.
5.3 Test arrangements
5.3.1 General
The conditions necessary to ensure satisfactory measurement of the characteristics of operation are defined
in this subclause, taking into account the accuracy required (see 6.2).
NOTE 1 The performance of a mixer in a given test arrangement, however accurately measured, cannot be assumed
to be a correspondingly accurate indication of its performance in another arrangement.
NOTE 2 Recommendations and general guidance about flow boundary arrangements to ensure satisfactory
measurements are given in Clause 7.
5.3.2 Standard test arrangements
The most suitable measuring conditions are obtained when the ambient flow surrounding the mixer is
minimized or completely eliminated. In particular,
a) large scale flow structures including vortices or swirl shall be eliminated/reduced,
b) if ambient flow cannot be eliminated, it shall be symmetric and parallel with the mixer impeller axis.
5.4 Test conditions
5.4.1 Test procedure
The duration of the test shall be sufficient to obtain consistent results regarding the degree of accuracy to be
achieved.
All measurements shall be made under steady conditions of operation, or under unsteady conditions within
the limits given in 5.4.2. A decision to make measurements when such conditions cannot be obtained shall be
a matter of agreement between the parties concerned.
Verification of the guarantee point shall be obtained by recording at least 30 readings closely and evenly
grouped in time, as specified in 5.2.2. Note that a larger number of readings may be required.
If the driving power available during a test on a test stand is insufficient, and if the test has to be carried out at
a reduced speed of rotation, the test results shall be translated to the specified speed of rotation in
accordance with 6.1.2. The speed of rotation shall be controlled in accordance with 5.4.4.
If the driving current available during a test on a test stand is insufficient because the SM is ∆-connected, a
−1/2 1/2
Y-connection may be applied at a current reduced by a factor 3 , and a voltage increased by a factor 3 ,
assuming 3-phase. Note that steady operation must be achieved before measurement readings are taken.
The difference in performance between the two connection types shall be accounted for in the test protocol.
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ISO 21630:2007(E)
5.4.2 Stability of operation
5.4.2.1 General remarks
For the purposes of this International Standard, the following shall be considered.
a) Fluctuations: short period changes in the measured value of a physical quantity about its mean value
during the time that a single reading is being made.
b) Variations: those changes in value which take place between one reading and next.
5.4.2.2 Permissible fluctuations in readings
If the signals delivered by the measuring systems are automatically recorded or integrated by the measuring
device, this International Standard does not specify a limit on the fluctuations. No such limitation is deemed
necessary if
a) the measuring system used includes an integrating device carrying out automatically, with the required
accuracy, the integration necessary to calculate the mean value over an integration period much longer
than the response time of the corresponding system;
b) the integration necessary to calculate the mean value may be carried out later on, from the continuous or
sampled record of the analog signal. (The sampling conditions should be specified in the test report.)
If none of these conditions is fulfilled, a limitation on fluctuations may be agreed on between
manufacturer/supplier and purchaser.
5.4.2.3 Number of sets of observations
5.4.2.3.1 General
A set of readings consists of a reading of each of the individual variables. In this International Standard, this
consists of a thrust reading and a power reading. Note that the thrust-to-power ratio is based on the final test
values of thrust and power.
5.4.2.3.2 Steady conditions
Test conditions are called steady if the mean value of all quantities involved (mixer thrust and power uptake)
are independent of time. In practice, test conditions may be regarded as steady if the maximum value
observed at the test operating point during at least 30 s of observation does not exceed the minimum
observed value during the same observation by more than 5 % of this minimum value. If this condition is met,
only one set of readings of individual quantities need be recorded.
5.4.2.3.3 Unsteady conditions
In such cases where the unsteadiness of test conditions give rise to doubts concerning the accuracy of the
tests, the following procedure shall be followed. The minimum number of readings of individual quantities is
given by the considerations in 6.2.2.
The measured variable is measured at instants separated by a constant period, or it is integrated and
averaged during a constant period. The period must be no shorter than half the auto-correlation period of the
measurement variable time series. If it is shorter by some factor, the number of readings of the individual
variable must be increased by the inverse of this factor.
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ISO 21630:2007(E)
The autocorrelation period, or auto-correlation time, of a measured variable x, with values + x measured
i
at times T + i ∆T, may be approximated as
initial
MN
2
⎡⎤
TT=∆ /σN+1 xx (1)
()
∑∑
0 ii+N
⎣⎦
Ni==0 1
where
N = M + 1 would produce the first negative contribution to the sum over N, and
∆T < T / 6 , N > 5 T /∆T.

0 0
The value of the standard deviation of the set of measurement values is σ.
5.4.3 Voltage
...