SIST EN ISO 14691:2009

SLOVENSKI STANDARD
01-februar-2009
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SIST EN ISO 14691:2001
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Petroleum, petrochemical and natural gas industries - Flexible couplings for mechanical
power transmission - General-purpose applications (ISO 14691:2008)
Erdöl-, petrochemische und Erdgasindustrie - Flexible Kupplungen für mechanische
Kraftübertragung - Allgemeine Anwendungsfälle (ISO 14691:2008)
Industries du pétrole, de la pétrochimie et du gaz naturel - Accouplements flexibles pour
transmission de puissance mécanique - Applications d'usage général (ISO 14691:2008)
Ta slovenski standard je istoveten z: EN ISO 14691:2008
ICS:
21.120.20 Sklopke Couplings
75.180.20 Predelovalna oprema Processing equipment
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN ISO 14691
NORME EUROPÉENNE
EUROPÄISCHE NORM
December 2008
ICS 75.180.20 Supersedes EN ISO 14691:2000
English Version
Petroleum, petrochemical and natural gas industries - Flexible
couplings for mechanical power transmission - General-purpose
applications (ISO 14691:2008)
Industries du pétrole, de la pétrochimie et du gaz naturel - Erdöl-, petrochemische und Erdgasindustrie - Flexible
Accouplements flexibles pour transmission de puissance Kupplungen für mechanische Kraftübertragung -
mécanique - Applications d'usage général (ISO Allgemeine Anwendungsfälle (ISO 14691:2008)
14691:2008)
This European Standard was approved by CEN on 28 November 2008.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European
Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national
standards may be obtained on application to the CEN Management Centre or to any CEN member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CEN member into its own language and notified to the CEN Management Centre has the same status as the
official versions.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal,
Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36  B-1050 Brussels
© 2008 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 14691:2008: E
worldwide for CEN national Members.

Contents Page
Foreword .3

Foreword
This document (EN ISO 14691:2008) has been prepared by Technical Committee ISO/TC 67 "Materials,
equipment and offshore structures for petroleum and natural gas industries" in collaboration with Technical
Committee CEN/TC 12 “Materials, equipment and offshore structures for petroleum, petrochemical and
natural gas industries”, the secretariat of which is held by AFNOR.
This European Standard shall be given the status of a national standard, either by publication of an identical
text or by endorsement, at the latest by June 2009, and conflicting national standards shall be withdrawn at
the latest by June 2009.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN ISO 14691:2000.
According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following
countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Cyprus, Czech
Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain,
Sweden, Switzerland and the United Kingdom.
Endorsement notice
The text of ISO 14691:2008 has been approved by CEN as a EN ISO 14691:2008 without any modification.

INTERNATIONAL ISO
STANDARD 14691
Second edition
2008-12-01
Petroleum, petrochemical and natural gas
industries — Flexible couplings for
mechanical power transmission —
General-purpose applications
Industries du pétrole, de la pétrochimie et du gaz naturel —
Accouplements flexibles pour transmission de puissance mécanique —
Applications d'usage général
Reference number
ISO 14691:2008(E)
©
ISO 2008
ISO 14691:2008(E)
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©  ISO 2008
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,
electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or
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Published in Switzerland
ii © ISO 2008 – All rights reserved

ISO 14691:2008(E)
Contents Page
Foreword. iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions. 2
4 Statutory requirements . 5
5 Coupling selection. 5
5.1 General. 5
5.2 Compliance. 6
6 Purchaser's specification . 6
7 Coupling rating . 8
8 Construction requirements. 9
8.1 General. 9
8.2 Materials of construction . 10
8.3 Coupling hubs. 11
8.4 Bolting. 12
8.5 Electrical insulation. 12
8.6 Alignment provision . 12
8.7 Rotor dynamic data . 12
8.8 Non-horizontal applications . 13
8.9 Additional requirements for gear couplings. 13
8.10 Additional requirements for metallic flexible-element couplings. 13
8.11 Additional requirements for elastomeric couplings . 13
9 Balance . 14
9.1 Objectives. 14
9.2 Balance quality. 14
9.3 Additional balancing requirements. 15
9.4 Verification of coupling balance . 15
10 Accessories. 15
11 Manufacturing quality, inspection, testing and preparation for shipment . 15
11.1 Manufacturing quality. 15
11.2 Inspection and testing. 16
11.3 Preparation for shipment . 16
12 Vendor's data . 16
12.1 General. 16
12.2 Proposals. 16
12.3 Contract data. 17
Annex A (informative) Examples of misalignment. 19
Annex B (informative) Example of the determination of potential unbalance . 21
Annex C (informative) Coupling tapers. 24
Annex D (normative) Coupling guards . 25
Annex E (informative) Coupling datasheets. 27
Bibliography . 32
ISO 14691:2008(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 14691 was prepared by Technical Committee ISO/TC 67, Materials, equipment and offshore structures
for petroleum, petrochemical and natural gas industries, Subcommittee SC 6, Processing equipment and
systems.
This second edition cancels and replaces the first edition (ISO 14691:1999), which has been technically
revised.
iv © ISO 2008 – All rights reserved

ISO 14691:2008(E)
Introduction
Users of this International Standard should be aware that further or differing requirements may be needed for
individual applications. This International Standard is not intended to inhibit a vendor from offering, or the
purchaser from accepting, alternative equipment or engineering solutions for the individual application. This
may be particularly appropriate where there is innovative or developing technology. Where an alternative is
offered, the vendor should identify any variations from this International Standard and provide details.
For the following applications, the use of ISO 10441 is recommended:
⎯ large or high-speed machines that may be required to operate continuously for extended periods, are
often unspared and are critical to the continued operation of the installation (special-purpose
applications);
⎯ machines in which the first lateral critical speed is less than the maximum required operating speed
(flexible-shaft machines);
⎯ machines in which the rotor dynamics are particularly sensitive to coupling unbalance.
This International Standard requires the purchaser to specify certain details and features. A bullet (●) at the
beginning of a subclause or paragraph indicates that either a decision is required or that further information is
to be provided by the purchaser. This information should be indicated on the datasheet(s), typical examples of
which are included as Annex E, otherwise it should be stated in the quotation request or in the order.
The coupling vendor is not normally required to supply the coupling guard or guards. However, for
completeness and for the information of the user of this International Standard, Annex D, which provides
requirements for guards, has been added.

INTERNATIONAL STANDARD ISO 14691:2008(E)

Petroleum, petrochemical and natural gas industries — Flexible
couplings for mechanical power transmission — General-
purpose applications
1 Scope
This International Standard specifies the requirements for couplings for the transmission of power between the
rotating shafts of two machines for general-purpose applications in the petroleum, petrochemical and natural
gas industries. Such applications typically require couplings to transmit power at speeds not exceeding
4 000 r/min, between machines in which the first lateral critical speed is above the running speed range (stiff-
shaft machines). It can, by agreement, be used for applications outside these limits.
NOTE 1 Recommendations are included in the Introduction as to when the use of ISO 10441 should be considered.
This International Standard is applicable to couplings designed to accommodate parallel (or lateral) offset,
angular misalignment and axial displacement of the shafts without imposing excessive mechanical loading on
the coupled machines. Couplings covered by this International Standard include gear (and other mechanical
contact types), metallic flexible-element and various elastomeric types. Such couplings can be of all metal
construction or can include components of non-metallic materials, such as composites.
This International Standard covers design, materials of construction, inspection and testing of couplings and
methods of attachment of the coupling to the shafts (including tapered sleeve and other proprietary devices).
This International Standard does not apply to special types of couplings, such as clutch, hydraulic, eddy-
current, rigid and radial-spline types.
This International Standard does not define criteria for the selection of coupling types for specific applications.
NOTE 2 In many cases, couplings covered by this International Standard are manufacturers' catalogue items.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 286-2:1988, ISO system of limits and fits — Part 2: Tables of standard tolerance grades and limit
deviations for holes and shafts
ISO 1940-1:2003, Mechanical vibration — Balance quality requirements for rotors in a constant (rigid) state —
Part 1: Specification and verification of balance tolerances
ISO 8821, Mechanical vibration — Balancing — Shaft and fitment key convention
ANSI/AGMA 9002, Bores and Keyways for Flexible Couplings (Inch Series)
ANSI/AGMA 9003, Flexible Couplings — Keyless Fits
ANSI/AGMA 9112, Bores and Keyways for Flexible Couplings (Metric Series)
ISO 14691:2008(E)
1)
DIN 7190, Interference fits — Calculation and design rules
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
angular misalignment
〈double-engagement couplings〉 two minor angles between the extension of each machine shaft centre-line
and the centre-line of the structure joining the two flexible elements
3.2
angular misalignment
〈single-engagement couplings〉 minor angle between the extensions of the shaft centre-lines of the two
coupled machines
3.3
axial displacement
change in the relative axial position of the adjacent shaft ends of two coupled machines, usually caused by
thermal expansion
3.4
continuous torque rating
coupling manufacturer's declared maximum torque that the coupling can transmit continuously for the
specified life
3.5
distance between shaft ends
DBSE
distance from the extreme end of one shaft (including any threaded end) to the extreme end of the next shaft
or, in the case of integral flanges, the distance from the mating faces
3.6
double-engagement coupling
coupling with two planes of flexure
NOTE This arrangement enables couplings of certain types, notably gear and metallic flexible-element types, that
cannot normally accommodate parallel (or lateral) offset, to do so.
3.7
gear coupling
coupling of the mechanical contact type that transmits torque and accommodates misalignment and axial
displacement by relative rocking and sliding motion between mating, profiled gear teeth
3.8
lateral offset
lateral distance between the centre-lines of two shafts that are not parallel, measured perpendicularly to the
centre-line and in the plane of the shaft end of the driving machine
See Annex A.
3.9
manufacturer
agency responsible for the design and fabrication of the coupling
NOTE The manufacturer is not necessarily the vendor.

1) Deutsches Institut für Normung, Burggrafenstraße 6, Berlin, Germany D-10787.
2 © ISO 2008 – All rights reserved

ISO 14691:2008(E)
3.10
maximum allowable speed
maximum speed for which the manufacturer has designed the coupling
3.11
maximum allowable temperature
maximum continuous temperature for which the manufacturer has designed the coupling
3.12
maximum continuous angular misalignment
maximum angular misalignment at each plane of flexure that the coupling is able to tolerate for the specified
life (5.1.3) when transmitting the coupling continuous torque rating at the coupling rated speed, and when
simultaneously subjected to the coupling maximum continuous axial displacement
3.13
maximum continuous axial displacement
maximum axial displacement the coupling is able to tolerate for the specified life (5.1.3) when transmitting the
coupling continuous torque rating at the coupling rated speed and when simultaneously subjected to the
coupling maximum continuous angular misalignment
3.14
maximum continuous speed
highest rotational speed at which the coupling, as made and tested, is capable of continuous operation
3.15
mechanical contact coupling
coupling designed to transmit torque by direct mechanical contact between mating parts and accommodate
misalignment and axial displacement by relative rocking and sliding motion between the parts in contact
NOTE 1 Examples of mechanical contact couplings are gear, grid, and pin-bushing couplings.
NOTE 2 The contacting parts can be metallic or can be made of self-lubricating non-metallic material.
NOTE 3 These couplings do not have a free-state position but resist change in the axial and angular direction, mainly
as a function of transmitted torque and the coefficient of friction between the contacting parts.
3.16
metallic flexible-element coupling
coupling that obtains its flexibility from the flexing of thin metallic discs, diaphragms or links
3.17
momentary torque limit
maximum instantaneous torque that the coupling can tolerate without suffering immediate failure
3.18
owner
final recipient of the equipment who may delegate another agent as the purchaser of the equipment
3.19
parallel offset
distance between the centre-lines of two coupled shafts that are parallel but not in the same straight line
See Annex A.
3.20
peak torque rating
maximum torque the coupling can tolerate for short periods
ISO 14691:2008(E)
3.21
pilot
rabbet
register
spigot
surface that positions a coupling component, sub-assembly, or assembly radially with respect to another
coupling component
3.22
potential unbalance
probable net unbalance of a complete coupling
NOTE 1 Potential unbalance results from a combination of the residual unbalance of individual components and
sub-assemblies and possible eccentricity of the components and sub-assemblies due to run-out and tolerances of the
various surfaces and registers. Since it can be assumed that the actual values of the various contributory unbalances are
random in both magnitude and direction, the numerical value of the potential unbalance is the square root of the sum of
the squares of all the contributory unbalances. Typical contributory unbalances are
a) the residual unbalance of each component or sub-assembly,
b) errors in the balance of each component or sub-assembly resulting from eccentricity in the fixture used to mount the
component or sub-assembly in the balance machine,
c) the unbalance of each component or sub-assembly due to eccentricity resulting from clearance or run-out of the
relevant registers or fits.
NOTE 2 The concept of potential unbalance is explained more fully, and a worked example is provided, in Annex B.
3.23
purchaser
agency that issues the order and the specification to the vendor
NOTE The purchaser can be the owner of the plant in which the equipment is being installed, the owner's appointed
agent or, frequently, the manufacturer of the driven machine.
3.24
rated speed
highest rotational speed at which the coupling is required to be capable of transmitting the continuous torque
rating while simultaneously subjected to the coupling rated axial displacement and the rated angular
misalignment (or the rated parallel or lateral offset in the case of a single-engagement coupling)
3.25
residual unbalance
level of unbalance remaining in a component or assembly after it has been balanced, either to the limit of the
capability of the balancing machine or in accordance with the relevant standard
3.26
service factor
factor applied to the steady-state torque in order to allow for off-design conditions, cyclic and other variations
as well as equipment variations resulting in a torque higher than that at the equipment normal operating point
3.27
single-engagement coupling
coupling with only one plane of flexure
NOTE This type of coupling can accommodate angular misalignment and axial displacement. Single-engagement
couplings of some types, notably gear and metallic flexible-element types, do not normally accommodate parallel (or
lateral) offset. Certain types of single-engagement couplings can accommodate offset misalignment to a limited extent.
3.28
spacer
part of a coupling that is removable to give access for maintenance and/or removal of the coupling hubs
NOTE The spacer can be a single component or an assembly.
4 © ISO 2008 – All rights reserved

ISO 14691:2008(E)
3.29
spacer gap length
distance between coupling hubs or sleeves in which the coupling spacer is installed
NOTE Spacer gap length is not necessarily equal to the distance between the shaft ends.
3.30
torsional stiffness
rate of change of the angular deflection with respect to the applied torque about the axis of rotation
NOTE With some types of couplings, the torsional stiffness is not constant but is a function of the magnitude of the
torque and, with oscillating torques, also the frequency.
3.31
trip speed
rotational speed at which the independent emergency overspeed device operates to shut down a variable-
speed prime mover or, for the purposes of this International Standard, in the case of alternating current
electric motors, the speed corresponding to the synchronous speed of the motor at line frequency or, in the
case of variable-frequency drives, at maximum supply frequency
3.32
unit responsibility
responsibility for co-ordinating the delivery and technical aspects of the equipment and all auxiliary systems
included in the scope of the order
NOTE The technical aspects for consideration include, but are not limited to, such factors as the power requirements,
speed, rotation, general arrangement, dynamics, noise, lubrication, sealing system, material test reports, instrumentation,
piping, conformance to specifications and testing of components.
3.33
vendor
supplier
agency that supplies the equipment
NOTE The vendor is the manufacturer of the equipment or the manufacturer's agent and normally is responsible for
service support.
4 Statutory requirements
The purchaser and the vendor shall mutually determine the measures taken to comply with any federal, state
or local codes, regulations, ordinances or rules that are applicable to the equipment.
5 Coupling selection
5.1 General
5.1.1 The coupling type, size and rating supplied in accordance with this International Standard may be
selected by one of the following methods.
⎯ Method A: The coupling is selected by the purchaser from the manufacturer's catalogue.
⎯ Method B: The coupling is selected by the purchaser from the manufacturer's catalogue and the selection
is agreed and approved by the vendor based on data supplied by the purchaser.
⎯ Method C: The coupling is recommended by the vendor based on data supplied by the purchaser.
ISO 14691:2008(E)
5.1.2 In the case of method A, before accepting an order, the vendor shall advise the purchaser if, based on
the information he has, he believes the coupling selected is not suitable for the application.
5.1.3 Unless otherwise agreed, couplings shall be designed, constructed and selected for a life of not less
than 5 years' continuous operation transmitting the continuous torque rating, at the rated speed and subjected
to the maximum continuous misalignment and axial displacement.
NOTE This requirement relates to the design of the coupling and does not imply a guaranteed life.
z If specified, the vendor shall provide evidence to demonstrate that this required life can be expected to be
achieved. This may be by providing details for the purchaser's inspection of one of the following:
⎯ at least three similar couplings in similar applications that have achieved a satisfactory life of at least
5 years in continuous service;
⎯ extended laboratory tests on similar complete couplings or on the highly stressed components;
⎯ fatigue analysis of the flexible elements and other highly stressed components where these are of a form
that is capable of precise stress analysis.
5.2 Compliance
5.2.1 To facilitate selection in methods A and B, the vendor's catalogue should clearly state that the
couplings described fully comply with the requirements of this International Standard or should clearly identify
the extent to which any particular type or model does not comply.
5.2.2 Where the necessary information is not included in the vendor's catalogue, and for selection
method C, the vendor shall state that the offered/recommended coupling complies with the requirements of
this International Standard or shall clearly identify the extent to which it does not comply.
6 Purchaser's specification
6.1 It is recommended that the information the purchaser is required to provide be specified by being
entered on a suitable data sheet, a typical form of which is given in Annex E. Where appropriate, the
information required should be provided in the form of sketches or diagrams.
z 6.2 If the purchaser makes his own selection from the vendor's catalogue, he should specify the type,
model and size of coupling required taking into account a suitable value for the service factor, K , and the
s
required misalignment and axial deflection capability.
The value of the service factor, K , should be selected to allow for torque variations due to the type of driving
s
and driven machines and possible future changes in the duty and should not generally be less than the values
in Table 1.
Table 1 — Service factors for electric motor and turbine prime movers
Driven machine K
s
Generator 1,2
Dynamic (centrifugal or axial) pump or compressor 1,25
Fan or rotary displacement pump or compressor 1,5
Reciprocating pump or compressor with four or more cylinders 1,75
Reciprocating pump or compressor with fewer than four cylinders 2,5
6 © ISO 2008 – All rights reserved

ISO 14691:2008(E)
z 6.3 If the coupling vendor is required to recommend a coupling (selection method C) or approve the
purchaser's selection (selection method B), the purchaser shall provide the following information:
a) make and type of driving and driven machine, and a description of the whole machine train if this is
comprised of more than two coupled units;
b) type of coupling (gear, flexible element, etc.) required and the method of attachment to the shafts;
c) rated speed (3.24), the equipment's operating speed range and the trip speed (3.31);
NOTE The rated speed is normally the maximum continuous speed.
d) maximum torque, T , that it is required to transmit;
m
NOTE The required continuous torque rating is not less than the maximum continuous torque that it is required to
transmit under any operating condition. Where one single machine is driven from a driver, the maximum continuous torque
is generally the maximum continuous torque of the driver. Where two or more machines are driven from one driver, either
in tandem through a multi-shaft gearbox or from both ends of the driver, the maximum continuous torque for each coupling
is generally based on the most adverse possible split of power consumption between the driven machines.
e) value used for the service factor, K , as defined in 3.26;
s
f) required misalignment capability, in terms of the angular misalignment and the parallel or lateral offset,
and the axial displacement that the coupling is required to accommodate;
g) expected magnitude, nature and number of occurrences of torsional transients that the coupling is
required to tolerate in service, without damage;
NOTE Torsional transients include start-up and shut-down effects, particularly those associated with synchronous
motors and variable-frequency drive systems.
h) environment in which the coupling is required to operate, including the maximum and minimum
temperatures and the presence of atmospheric contaminants likely to attack the components of the
coupling.
z 6.4 The purchaser may specify the axial distance between the extreme ends of the shafts of the two
machines being coupled, in the cold static condition. Alternatively, the purchaser may accept the vendor's
standard or proposed coupling length.
z 6.5 If relevant, the purchaser should also specify the expected magnitude of momentary torques, resulting
from fault conditions, which the coupling is required to survive but possibly with some damage. In particular, in
the case of a generator drive, the purchaser should specify the short-circuit torque.
NOTE It is accepted that, after such an event, the coupling will be need to be inspected and components replaced as
necessary.
z 6.6 The purchaser may state if any properties of the coupling are considered important from consideration
of the rotor dynamics of the driving or driven machines, or for any other reason, and may specify the range of
acceptable values. Such properties may, for example, include
⎯ overhung mass,
⎯ torsional stiffness,
⎯ coupling axial reaction force (8.1.4),
⎯ coupling lateral stiffness, that is, the transverse load on the shafts resulting from unit parallel offset,
ISO 14691:2008(E)
⎯ coupling bending stiffness, that is, the bending moment imposed on the shafts resulting from unit angular
misalignment.
NOTE It is not expected that this will be necessary for the majority of general-purpose applications.
z 6.7 The purchaser may indicate a requirement for a coupling design that either maintains or disconnects
the drive in the event of failure of the flexing elements.
7 Coupling rating
7.1 To facilitate coupling selection methods A and B, the vendor's catalogue shall, for each type, model and
size of coupling, clearly indicate
a) the coupling continuous torque rating,
b) the maximum continuous angular misalignment at each plane of flexure,
c) the maximum continuous axial displacement in each direction,
d) the maximum continuous parallel or lateral offset for single engagement couplings,
e) the maximum allowable speed,
f) the maximum continuous speed,
g) the maximum allowable temperature.
7.2 Where the vendor has been required to propose a coupling (selection method C), the vendor shall
provide the data listed in 7.1 for the particular coupling offered in his proposal.
7.3 The coupling continuous torque rating, T (3.4), shall be not less than the value determined by
c
Equation (1):
TT=×K (1)
cm s
where
T is maximum torque that it is necessary to transmit;
m
K is the coupling service factor.
s
Should the purchaser fail to specify a value for K , the vendor may, for the purpose of initial selection of a
s
coupling, assume a value not less than the appropriate value from Table 1. The vendor shall clearly state his
assumed value in his proposal.
7.4 The maximum allowable speed shall not be less than the trip speed.
7.5 The maximum continuous speed of the coupling shall not be less than the rated speed.
7.6 The maximum continuous angular misalignment at each plane of flexure shall be not less than that
required [6.3, item f)] or 0,1°, whichever is the greater.
7.7 The maximum continuous axial displacement in either direction from the neutral state, shall be not less
than the greatest of
⎯ that required by the purchaser [6.3, item f)];
8 © ISO 2008 – All rights reserved

ISO 14691:2008(E)
⎯ 1,5 % of the diameter of the driving or driven machine shaft, whichever is larger;
⎯ 1 mm.
The neutral state of a flexible-element coupling is the cold, unloaded state. The neutral state of a gear or other
mechanical contact coupling is the central position.
7.8 The maximum continuous parallel or lateral offset of a single-engagement coupling shall not be less
than the greatest of
⎯ that required by the purchaser [6.3, item f)];
⎯ 0,5 % of the diameter of the driving or driven machine shaft, whichever is larger;
⎯ 0,25 mm.
7.9 The vendor shall state the relationship between the coupling continuous torque, the coupling continuous
misalignment and the coupling continuous axial displacement if the rated maximum values of each cannot be
accepted simultaneously.
NOTE 1 With some types of coupling, particularly those with elastomeric elements or inserts, this relationship can also
be a function of temperature.
The most severe combination of angular misalignment and lateral offset shall be assumed.
NOTE 2 For double-engagement couplings, the most severe combination normally occurs when the two forms of
misalignment are in the same plane and in the same direction (see Figure A.3).
7.10 The coupling shall be capable of transmitting 115 % of the purchaser-specified maximum transient
torque as specified in 6.3, item g), for sufficient duration and frequency to satisfy the operational requirements
as specified in 6.3, item g), without damage. If the purchaser has failed to specify the expected transients, the
coupling shall be capable of transmitting, without damage, a cyclic torque of amplitude (zero to maximum)
equal to twice the maximum torque, T , that it is required to transmit for not less than 10 cycles.
m
z 7.11 The coupling shall be strong enough to survive the momentary fault-condition torques specified in
accordance with 6.5, albeit with some damage. Alternatively, if specified, the coupling shall incorporate an
agreed type of torque-limiting feature to prevent damage to the coupling or to the coupled equipment.
8 Construction requirements
8.1 General
z 8.1.1 If specified, the coupling design shall be such that the flexible element or elements or inserts, and/or
the components carrying the gear teeth or other wearing parts, can be removed and replaced without the
requirement to move either the driving or the driven machine or otherwise disturb the alignment.
z 8.1.2 If specified, the design shall be such that the coupling, including hubs, can be completely dismantled
and removed to facilitate the maintenance of adjacent bearings and/or seals, without either removing the shaft
or disturbing the equipment alignment. The purchaser shall specify the minimum spacer gap length (3.29)
required.
z 8.1.3 If specified, the coupling shall be of the limited-end-float design. The purchaser shall specify the end-
float required and the maximum axial force the coupling is required to transmit.
NOTE The most common situation in which a limited-end-float coupling is required is with a sleeve-bearing motor
without an axial bearing. It is not generally necessary to provide a positive-stop, limited-end-float design with flexible-
element couplings, provided that the axial stiffness (spring rate) of the coupling is sufficient to hold the motor rotor within
its axial limits during normal operation, start-up and shut-down.
ISO 14691:2008(E)
8.1.4 The vendor shall state the maximum coupling axial reaction force. In the case of gear couplings and
other mechanical contact types, this shall be based on the friction between the teeth or other elements under
the coupling rated torque; the vendor shall state the assumed value of the friction factor. In the case of
flexible-element couplings, the vendor shall provide a curve of axial force versus axial displacement and shall
state the maximum acceptable axial displacement.
The coupling axial reaction force is the axial force developed within the coupling resulting from the imposed
operating conditions and is a function of the shape and stiffness of the flexible elements or the sliding friction
between the elements of a mechanical-contact coupling.
NOTE Examples of imposed operating conditions are axial displacement, misalignment, speed, temperature, etc.
z 8.1.5 For double-engagement couplings with a distance between the planes of flexure greater than 50 cm,
the vendor shall ensure that either the first lateral resonant frequency of the floating shaft is not less than twice
the maximum speed at which the coupling is required to operate (normally the maximum continuous speed),
or shall notify the purchaser of the actual value. Details of the method used to determine the first lateral
resonant frequency shall be made available for review by the purchaser, if required.
The floating shaft is the component, or assembly of components, of a double-engagement coupling between,
and supported from, the two planes of flexure.
8.1.6 All major parts (hubs, spacers, etc., but excluding flexible elements and fasteners) shall be indelibly
marked such that they can be uniquely identified. Marking shall be applied in a low-stress area and shall not
affect the performance or integrity of the coupling.
8.2 Materials of construction
8.2.1 Except as required or prohibited by this International Standard or by the purchaser, materials of
construction shall be to the vendor's stan
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