# SIST EN 60534-2-1:2011

(Main)## Industrial-process control valves - Part 2-1: Flow capacity - Sizing equations for fluid flow under installed conditions (IEC 60534-2-1:2011)

## Industrial-process control valves - Part 2-1: Flow capacity - Sizing equations for fluid flow under installed conditions (IEC 60534-2-1:2011)

This part of IEC 60534 includes equations for predicting the flow of compressible and incompressible fluids through control valves. The equations for incompressible flow are based on standard hydrodynamic equations for Newtonian incompressible fluids. They are not intended for use when non-Newtonian fluids, fluid mixtures, slurries or liquid-solid conveyance systems are encountered. The equations for incompressible flow may be used with caution for non-vaporizing multi-component liquid mixtures. Refer to Clause 6 for additional information.

## Stellventile für die Prozessregelung - Teil 2-1: Durchflusskapazität - Bemessungsgleichungen für Fluide unter Betriebsbedingungen (IEC 60534-2-1:2011)

## Vannes de régulation des processus industriels - Partie 2-1: Capacité d'écoulement - Equations de dimensionnement pour l'écoulement des fluides dans les conditions d'installation (CEI 60534-2-1:2011)

La CEI 60534-2-1:2011 comprend des équations permettant de prévoir le débit de fluides compressibles et incompressibles dans les vannes de régulation. Les équations relatives à l'écoulement des fluides incompressibles sont fondées sur les équations de base applicables aux fluides newtoniens incompressibles. Elles ne sont pas destinées à être utilisées pour des fluides non newtoniens, des mélanges de fluides, des boues ou des systèmes transportant des particules solides en suspension dans un liquide. Les équations relatives à l'écoulement des fluides incompressibles peuvent être utilisées, mais avec prudence, pour les mélanges liquides à composants multiples non volatils. Cette deuxième édition annule et remplace la première édition parue en 1998. Cette édition constitue une révision technique. Elle inclut les modifications techniques majeures suivantes par rapport à l'édition précédente: - les mêmes modèles fondamentaux de débit mais modifie l'organisation des équations pour simplifier l'utilisation de la norme en introduisant la notion de Δ*p*_{dim}; - des changements dans les corrections pour les fluides non turbulents et dans les moyens d'obtention des résultats; - le passage des calculs multi-étagés en Annexe.

## Regulacijski ventili za industrijske procese - 2-1. del: Kapaciteta pretoka - Enačbe za določanje pretoka tekočin pri postavljenih pogojih (IEC 60534-2-1:2011)

Ta del IEC 60534 vključuje enačbe za napovedovanje pretoka stisljivih in nestisljivih tekočin skozi regulacijske ventile. Enačbe za nestisljiv pretok so zasnovane na standardnih hidrodinamičnih enačbah za newtonske nestisljive tekočine. Niso namenjene, da se uporabijo, kadar naletimo na tekočine, ki niso newtonske, mešanice tekočin, pastaste tekočine ali transportne sisteme za tekočine-trdnine. Enačbe za pretok nestisljivih tekočin morajo biti uporabljene pozorno pri hlapljivih večkomponentnih tekočih mešanicah. Dodatne informacije so na voljo v točki 6.

### General Information

### Relations

### Standards Content (Sample)

SLOVENSKI STANDARD

SIST EN 60534-2-1:2011

01-julij-2011

1DGRPHãþD

SIST EN 60534-2-1:2001

5HJXODFLMVNLYHQWLOL]DLQGXVWULMVNHSURFHVHGHO.DSDFLWHWDSUHWRND(QDþEH

]DGRORþDQMHSUHWRNDWHNRþLQSULSRVWDYOMHQLKSRJRMLK,(&

Industrial-process control valves - Part 2-1: Flow capacity - Sizing equations for fluid flow

under installed conditions (IEC 60534-2-1:2011)

Stellventile für die Prozessregelung - Teil 2-1: Durchflusskapazität -

Bemessungsgleichungen für Fluide unter Betriebsbedingungen (IEC 60534-2-1:2011)

Vannes de régulation des processus industriels - Partie 2-1: Capacité d'écoulement -

Equations de dimensionnement pour l'écoulement des fluides dans les conditions

d'installation (CEI 60534-2-1:2011)

Ta slovenski standard je istoveten z: EN 60534-2-1:2011

ICS:

23.060.40 7ODþQLUHJXODWRUML Pressure regulators

25.040.40 Merjenje in krmiljenje Industrial process

industrijskih postopkov measurement and control

SIST EN 60534-2-1:2011 en

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------

SIST EN 60534-2-1:2011

---------------------- Page: 2 ----------------------

SIST EN 60534-2-1:2011

EUROPEAN STANDARD

EN 60534-2-1

NORME EUROPÉENNE

May 2011

EUROPÄISCHE NORM

ICS 23.060.40; 25.040.40 Supersedes EN 60534-2-1:1998

English version

Industrial-process control valves -

Part 2-1: Flow capacity -

Sizing equations for fluid flow under installed conditions

(IEC 60534-2-1:2011)

Vannes de régulation des processus Stellventile für die Prozessregelung -

industriels - Teil 2-1: Durchflusskapazität -

Partie 2-1: Capacité d'écoulement - Bemessungsgleichungen für Fluide unter

Equations de dimensionnement pour Betriebsbedingungen

l'écoulement des fluides dans les (IEC 60534-2-1:2011)

conditions d'installation

(CEI 60534-2-1:2011)

This European Standard was approved by CENELEC on 2011-05-04. CENELEC 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 Central Secretariat or to any CENELEC 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 CENELEC member into its own language and notified

to the Central Secretariat has the same status as the official versions.

CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus,

the Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy,

Latvia, Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia,

Spain, Sweden, Switzerland and the United Kingdom.

CENELEC

European Committee for Electrotechnical Standardization

Comité Européen de Normalisation Electrotechnique

Europäisches Komitee für Elektrotechnische Normung

Management Centre: Avenue Marnix 17, B - 1000 Brussels

© 2011 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.

Ref. No. EN 60534-2-1:2011 E

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SIST EN 60534-2-1:2011

EN 60534-2-1:2011 - 2 -

Foreword

The text of document 65B/783/FDIS, future edition 2 of IEC 60534-2-1, prepared by SC 65B, Devices &

process analysis, of IEC TC 65, Industrial-process measurement, control and automation, was submitted

to the IEC-CENELEC parallel vote and was approved by CENELEC as EN 60534-2-1 on 2011-05-04.

This European Standard supersedes EN 60534-2-1:1998.

EN 60534-2-1:2011 includes the following significant technical changes with respect to

EN 60534-2-1:1998:

— the same fundamental flow model, but changes the equation framework to simplify the use of the

standard by introducing the notion of ∆p ;

sizing

— changes to the non-turbulent flow corrections and means of computing results;

— multi-stage sizing as an Annex.

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. CEN and CENELEC shall not be held responsible for identifying any or all such patent

rights.

The following dates were fixed:

– latest date by which the EN has to be implemented

at national level by publication of an identical

national standard or by endorsement (dop) 2012-02-04

– latest date by which the national standards conflicting

with the EN have to be withdrawn (dow) 2014-05-04

Annex ZA has been added by CENELEC.

__________

Endorsement notice

The text of the International Standard IEC 60534-2-1:2011 was approved by CENELEC as a European

Standard without any modification.

__________

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SIST EN 60534-2-1:2011

- 3 - EN 60534-2-1:2011

Annex ZA

(normative)

Normative references to international publications

with their corresponding European publications

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.

NOTE When an international publication has been modified by common modifications, indicated by (mod), the relevant EN/HD

applies.

Publication Year Title EN/HD Year

IEC 60534-1 2005 Industrial-process control valves - EN 60534-1 2005

Part 1: Control valve terminology and general

considerations

IEC 60534-2-3 1997 Industrial-process control valves - EN 60534-2-3 1998

Part 2-3: Flow capacity - Test procedures

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SIST EN 60534-2-1:2011

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SIST EN 60534-2-1:2011

IEC 60534-2-1

®

Edition 2.0 2011-03

INTERNATIONAL

STANDARD

NORME

INTERNATIONALE

Industrial-process control valves –

Part 2-1: Flow capacity – Sizing equations for fluid flow under installed

conditions

Vannes de régulation des processus industriels –

Partie 2-1: Capacité d'écoulement – Equations de dimensionnement pour

l'écoulement des fluides dans les conditions d'installation

INTERNATIONAL

ELECTROTECHNICAL

COMMISSION

COMMISSION

ELECTROTECHNIQUE

PRICE CODE

INTERNATIONALE

CODE PRIX XA

ICS 23.060.40; 25.040.40 ISBN 978-2-88912-399-5

® Registered trademark of the International Electrotechnical Commission

Marque déposée de la Commission Electrotechnique Internationale

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SIST EN 60534-2-1:2011

– 2 – 60534-2-1 IEC:2011

CONTENTS

FOREWORD . 4

1 Scope . 6

2 Normative references . 6

3 Terms and definitions . 7

4 Symbols . 8

5 Installation . 9

6 Sizing equations for incompressible fluids . 10

6.1 Turbulent flow . 10

6.2 Pressure differentials . 11

6.2.1 Sizing pressure differential, ∆p . 11

sizing

6.2.2 Choked pressure differential, ∆p . 11

choked

6.2.3 Liquid critical pressure ratio factor, F . 11

F

6.3 Non-turbulent (laminar and transitional) flow . 11

7 Sizing equations for compressible fluids . 11

7.1 General . 11

7.2 Pressure differentials . 12

7.2.1 Sizing pressure drop ratio, x . 12

sizing

7.2.2 Choked pressure drop ratio, x . 12

choked

7.3 Specific heat ratio factor, F . 12

γ

7.4 Expansion factor, Y . 13

7.5 Compressibility factor, Z . 13

7.6 Non-turbulent (laminar and transitional) flow . 14

8 Correction factors common to both incompressible and compressible flow . 14

8.1 Piping geometry correction factors . 14

8.2 Estimated piping geometry factor, F . 14

P

8.3 Estimated combined liquid pressure recovery factor and piping geometry

factor with attached fittings, F . 15

LP

8.4 Estimated pressure differential ratio factor with attached fittings, x . 16

TP

9 Reynolds Number, Re . 16

V

Annex A (normative) Sizing equations for non-turbulent flow . 18

Annex B (normative) Sizing equations for fluid flow through multistage control valves. 21

Annex C (informative) Piping factor computational considerations . 28

Annex D (informative) Engineering Data . 34

Annex E (informative) Reference calculations . 41

Bibliography . 54

Figure 1 – Reference pipe section for sizing . 10

Figure B.1 – Multistage multipath trim . 23

Figure B.2 – Multistage single path trim . 24

Figure B.3 – Disk from a continuous resistance trim The complete trim consists of a

number of these disks stacked together. . 25

Figure B.4 – Sectional view of continuous resistance trim with multiple flow passages

having vertical undulations . 25

Figure C.1 – Determination of the upper limit of the flow coefficient by the iterative

method . 32

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SIST EN 60534-2-1:2011

60534-2-1 IEC:2011 – 3 –

Figure C.2 – Determination of the final flow coefficient by the iterative method . 33

Figure D.1 – Piping geometry factors . 37

Figure D.2 – Pressure recovery factors . 39

Figure D.3 – Liquid critical pressure ratio factor F . 40

F

Table 1 – Numerical constants N . 17

Table B.1 – Values of the stage interaction factors, k, and the reheat factors, r for

multistage single and multipath control valve trim . 27

Table B.2 – Values of the stage interaction factors, k, and the reheat factors, r for

continuous resistance control valve trim . 27

Table C.1 – Incompressible flow . 31

Table C.2 – Compressible flow . 31

Table D.1 – Typical values of valve style modifier F , liquid pressure recovery factor F

d L

a)

and pressure differential ratio factor x at full rated travel . 35

T

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SIST EN 60534-2-1:2011

– 4 – 60534-2-1 IEC:2011

INTERNATIONAL ELECTROTECHNICAL COMMISSION

____________

INDUSTRIAL-PROCESS CONTROL VALVES –

Part 2-1: Flow capacity –

Sizing equations for fluid flow under installed conditions

FOREWORD

1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising

all national electrotechnical committees (IEC National Committees). The object of IEC is to promote

international co-operation on all questions concerning standardization in the electrical and electronic fields. To

this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,

Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC

Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested

in the subject dealt with may participate in this preparatory work. International, governmental and non-

governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely

with the International Organization for Standardization (ISO) in accordance with conditions determined by

agreement between the two organizations.

2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international

consensus of opinion on the relevant subjects since each technical committee has representation from all

interested IEC National Committees.

3) IEC Publications have the form of recommendations for international use and are accepted by IEC National

Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC

Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any

misinterpretation by any end user.

4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications

transparently to the maximum extent possible in their national and regional publications. Any divergence

between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in

the latter.

5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity

assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any

services carried out by independent certification bodies.

6) All users should ensure that they have the latest edition of this publication.

7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and

members of its technical committees and IEC National Committees for any personal injury, property damage or

other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and

expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC

Publications.

8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is

indispensable for the correct application of this publication.

9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of

patent rights. IEC shall not be held responsible for identifying any or all such patent rights.

International Standard IEC 60534-2-1 has been prepared by subcommittee 65B: Measurement

and control devices, of IEC technical committee 65: Industrial-process measurement, control

and automation.

This second edition cancels and replaces the first edition published in 1998. This edition

constitutes a technical revision.

This edition includes the following significant technical changes with respect to the previous

edition:

• the same fundamental flow model, but changes the equation framework to simplify the

use of the standard by introducing the notion of ∆p ;

sizing

• changes to the non-turbulent flow corrections and means of computing results;

• multi-stage sizing as an Annex.

The text of this standard is based on the following documents:

---------------------- Page: 10 ----------------------

SIST EN 60534-2-1:2011

60534-2-1 IEC:2011 – 5 –

FDIS Report on voting

65B/783/FDIS 65B/786/RVD

Full information on the voting for the approval of this standard can be found in the report on

voting indicated in the above table.

This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.

A list of all the parts of the IEC 60534 series, under the general title Industrial-process control

valves, can be found on the IEC website.

The committee has decided that the contents of this publication will remain unchanged until

the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data

related to the specific publication. At this date, the publication will be

• reconfirmed,

• withdrawn,

• replaced by a revised edition, or

• amended.

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SIST EN 60534-2-1:2011

– 6 – 60534-2-1 IEC:2011

INDUSTRIAL-PROCESS CONTROL VALVES –

Part 2-1: Flow capacity –

Sizing equations for fluid flow under installed conditions

1 Scope

This part of IEC 60534 includes equations for predicting the flow of compressible and

incompressible fluids through control valves.

The equations for incompressible flow are based on standard hydrodynamic equations for

Newtonian incompressible fluids. They are not intended for use when non-Newtonian fluids,

fluid mixtures, slurries or liquid-solid conveyance systems are encountered. The equations for

incompressible flow may be used with caution for non-vaporizing multi-component liquid

mixtures. Refer to Clause 6 for additional information.

At very low ratios of pressure differential to absolute inlet pressure (∆p/p ), compressible

1

fluids behave similarly to incompressible fluids. Under such conditions, the sizing equations

for compressible flow can be traced to the standard hydrodynamic equations for Newtonian

incompressible fluids. However, increasing values of ∆p/p result in compressibility effects

1

which require that the basic equations be modified by appropriate correction factors. The

equations for compressible fluids are for use with ideal gas or vapor and are not intended for

use with multiphase streams such as gas-liquid, vapor-liquid or gas-solid mixtures.

Reasonable accuracy can only be maintained when the specific heat ratio, γ, is restricted to

the range 1,08 < γ < 1,65. Refer to Clause 7.2 for more information.

For compressible fluid applications, this standard is valid for valves with x ≤ 0,84 (see Table

T

D.2). For valves with x > 0,84 (e.g. some multistage valves), greater inaccuracy of flow

T

prediction can be expected.

Reasonable accuracy can only be maintained for control valves if:

C

< 0,047

2

N d

18

Note that while the equation structure utilized in this document departs radically from previous

versions of the standard, the basic technology is relatively unchanged. The revised equation

format was adopted to simplify presentation of the various equations and improve readability

of the document.

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.

IEC 60534-1:2005, Industrial-process control valves – Part 1: Control valve terminology and

general considerations

IEC 60534-2-3:1997, Industrial-process control valves – Part 2-3: Flow capacity – Test

procedures

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SIST EN 60534-2-1:2011

60534-2-1 IEC:2011 – 7 –

3 Terms and definitions

For the purposes of this document, the terms and definitions given in IEC 60534-1, and the

following apply.

3.1

valve style modifier

the ratio of the hydraulic diameter of a single flow passage to the diameter of a circular

orifice, the area of which is equivalent to the sum of areas of all identical flow passages at a

given travel. It should be stated by the manufacturer as a function of travel (see Annex A).

3.2

standard volumetric flowrates

compressible fluid volumetric flow rates in cubic metres per hour, identified by the symbol Q ,

S

refer to either

a) Standard conditions, which is an absolute pressure of 1 013,25 mbar and a

temperature of 288,6 K, or

b) Normal conditions, which is an absolute pressure of 1 013,25 mbar and a temperature

of 273 K.

Numerical constants for the flow equations are provided for both conventions (see Table 1).

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SIST EN 60534-2-1:2011

– 8 – 60534-2-1 IEC:2011

4 Symbols

Symbo Description Unit

l

C Flow coefficient (K , C ) Various (see IEC 60534-1)

v v

(see Note 4)

d Nominal valve size mm

D Internal diameter of the piping mm

D Internal diameter of upstream piping mm

1

D Internal diameter of downstream piping mm

2

D Orifice diameter mm

o

F Valve style modifier (see Annex A) Dimensionless

d

(see Note 4)

F Liquid critical pressure ratio factor Dimensionless

F

F Liquid pressure recovery factor of a control valve without attached fittings Dimensionless

L

(see Note 4)

F Combined liquid pressure recovery factor and piping geometry factor of a Dimensionless

LP

control valve with attached fittings

F Piping geometry factor Dimensionless

P

F Reynolds number factor Dimensionless

R

F Specific heat ratio factor Dimensionless

γ

M Molecular mass of flowing fluid kg/kmol

N Numerical constants (see Table 1) Various (see Note 1)

p Inlet absolute static pressure measured at point A (see Figure 1) kPa or bar (see Note 2)

1

p Outlet absolute static pressure measured at point B (see Figure 1) kPa or bar

2

p Absolute thermodynamic critical pressure kPa or bar

c

p Reduced pressure (p /p ) Dimensionless

r 1 c

p Absolute vapour pressure of the liquid at inlet temperature kPa or bar

v

∆p Differential pressure between upstream and downstream pressure taps kPa or bar

actual

(P – P )

1 2

Computed value of limiting pressure differential for incompressible flow kPa or bar

∆p

choked

∆p Value of pressure differential used in computing flow or required flow kPa or bar

sizing

coefficient for incompressible flows

3

Q Actual volumetric flow rate m /h

3

Q Standard volumetric flow rate (see definition 3.2) m /h

S

Re Valve Reynolds number Dimensionless

v

T Inlet absolute temperature K

1

T Absolute thermodynamic critical temperature K

c

T Reduced temperature (T /T ) Dimensionless

r 1 c

t Absolute reference temperature for standard cubic metre K

s

W Mass flow rate kg/h

x Dimensionless

Ratio of actual pressure differential to inlet absolute pressure (∆P/P )

1

x Choked pressure drop ratio for compressible flow Dimensionless

choked

x Value of pressure drop ratio used in computing flow or required flow Dimensionless

sizing

coefficient for compressible flows

---------------------- Page: 14 ----------------------

SIST EN 60534-2-1:2011

60534-2-1 IEC:2011 – 9 –

Symbo Description Unit

l

x Pressure differential ratio factor of a control valve without attached fittings Dimensionless

T

at choked flow (see Note 4)

x Pressure differential ratio factor of a control valve with attached fittings at Dimensionless

TP

choked flow

Y Expansion factor Dimensionless

Z Compressibility factor at inlet conditions Dimensionless

1

2

ν Kinematic viscosity m /s (see Note 3)

3

Density of fluid at p and T kg/m

ρ

1 1

1

Dimensionless

ρ /ρ Relative density (ρ /ρ = 1,0 for water at 15 °C)

1 o 1 o

Specific heat ratio Dimensionless

γ

ζ Velocity head loss coefficient of a reducer, expander or other fitting Dimensionless

attached to a control valve or valve trim

Upstream velocity head loss coefficient of fitting Dimensionless

ζ

1

ζ Downstream velocity head loss coefficient of fitting Dimensionless

2

ζ Inlet Bernoulli coefficient Dimensionless

B1

Outlet Bernoulli coefficient Dimensionless

ζ

B2

NOTE 1 To determine the units for the numerical constants, dimensional analysis may be performed on the

appropriate equations using the units given in Table 1.

2 5

NOTE 2 1 bar = 10 kPa = 10 Pa

–6 2

NOTE 3 1 centistoke = 10 m /s

NOTE 4 These values are travel-related and should be stated by the manufacturer.

5 Installation

In many industrial applications, reducers or other fittings are attached to the control valves.

The effect of these types of fittings on the nominal flow coefficient of the control valve can be

significant. A correction factor is introduced to account for this effect. Additional factors are

introduced to take account of the fluid property characteristics that influence the flow capacity

of a control valve.

In sizing control valves, using the relationships presented herein, the flow coefficients calculated

are assumed to include all head losses between points A and B, as shown in Figure 1.

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SIST EN 60534-2-1:2011

– 10 – 60534-2-1 IEC:2011

Flow

l l

1 2

Pressure tap Pressure tap

A B

Control valve with or without attached fittings

IEC 509/11

l = two nominal pipe diameters

1

l = six nominal pipe diameters

2

Figure 1 – Reference pipe section for sizing

6 Sizing equations for incompressible fluids

6.1 Turbulent flow

The fundamental flow model for incompressible fluids in the turbulent flow regime is given as:

∆p

sizing

Q = CN F (1)

1 P

ρ

1

ρ

o

NOTE 1 The numerical constant N depends on the units used in the general sizing equation and the type of flow

1

coefficient: K or C .

v v

NOTE 2 The piping geometry factor, F , reduces to unity when the valve size and adjoining pipe sizes are

P

identical. Refer to 8.1 for evaluation and additional information.

This model establishes the relationship between flow rate, flow coefficient, fluid properties,

related installation factors, and pertinent service conditions for control valves handling

incompressible fluids. Equation (1) may be used to compute the required flow coefficient, the

flow rate or applied pressure differential given any two of the three quantities.

This model rigorously applies only to single component, single phase fluids (i.e., no multi-

phase mixtures, no multi-component mixtures). However, this model may be used with caution

under certain conditions for multi-component mixtures in the liquid phase. The underlying

assumptions of the flow model would be satisfied for liquid-liquid fluid mixtures subject to the

following restrictions:

• the mixture is homogenous;

• the mixture is in chemical and thermodynamic equilibrium;

• the entire throttling process occurs well away from the multiphase region.

When these conditions are satisfied, the mixture density should be substituted for the fluid

density ρ in Equation (1).

1

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SIST EN 60534-2-1:2011

60534-2-1 IEC:2011 – 11 –

6.2 Pressure differentials

6.2.1 Sizing pressure differential, ∆p

sizing

The value of the pressure differential used in Equation (1) to predict flow rate or compute a

required flow coefficient is the lesser of the actual pressure differential or the choked pressure

differential:

∆p if ∆p < ∆p

choked

∆p = (2)

sizing

∆p if ∆p ≥ ∆p

choked choked

6.2.2 Choked pressure differential, ∆p

choked

The condition where further increase in pressure differential at constant upstream pressure no

longer produces a corresponding increase in flow through the control valve is designated

“choked flow”. The pressure drop at which this occurs is known as the choked pressure

differential and is given by the following equation:

2

F

LP

∆p = (p − F p ) (3)

choked 1 F v

F

P

2

F

LP 2

NOTE The expression ( ) reduces to F when the valve size and adjoining pipe sizes are identical. Refer to

L

F

P

8.1 for more information.

6.2.3 Liquid critical pressure ratio factor, F

F

**...**

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