Fluid flow in closed conduits — Connections for pressure signal transmissions between primary and secondary elements

ISO 2186:2007 sets out provisions for the design, lay-out and installation of a pressure signal transmission system, whereby a pressure signal from a primary fluid flow device can be transmitted by known techniques to a secondary device safely and in such a way that the value of the signal is not distorted or modified.

Débit des fluides dans les conduites fermées — Liaisons pour la transmission du signal de pression entre les éléments primaires et secondaires

Pretok tekočin v zaprtih kanalih - Povezave za prenos signala tlaka med primarnimi in sekundarnimi elementi

Ta mednarodni standard postavlja določbe za načrtovanje, razporeditev in namestitev sistema za prenos signala tlaka, kjer se signal tlaka iz primarne naprave za pretok tekočine lahko varno prenese z znanimi tehnikami do sekundarne naprave na tak način, da se vrednost signala ne popači ali spremeni.

General Information

Status
Published
Publication Date
27-Feb-2007
Current Stage
9093 - International Standard confirmed
Start Date
22-Nov-2013
Completion Date
09-Dec-2020

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INTERNATIONAL ISO
STANDARD 2186
Second edition
2007-03-01
Fluid flow in closed conduits —
Connections for pressure signal
transmissions between primary and
secondary elements
Débit des fluides dans les conduites fermées — Liaisons pour la
transmission du signal de pression entre les éléments primaires et
secondaires
Reference number
ISO 2186:2007(E)
ISO 2007
---------------------- Page: 1 ----------------------
ISO 2186:2007(E)
PDF disclaimer

This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but shall

not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In

downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat

accepts no liability in this area.
Adobe is a trademark of Adobe Systems Incorporated.

Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation

parameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In the

unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below.

© ISO 2007

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

ISO's member body in the country of the requester.
ISO copyright office
Case postale 56  CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
Web www.iso.org
Published in Switzerland
ii ISO 2007 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 2186:2007(E)
Contents Page

1 Scope .................................................................................................................................................... 1

2 Normative references .......................................................................................................................... 1

3 Terms and definitions .......................................................................................................................... 1

4 General principles ............................................................................................................................... 1

4.1 Safe containment ................................................................................................................................ 1

4.2 Piping specification ............................................................................................................................ 2

4.3 Isolation (block) valves ....................................................................................................................... 3

4.4 Valve manifolds ................................................................................................................................... 3

4.5 Installation ........................................................................................................................................... 4

4.6 Pressure taps ....................................................................................................................................... 5

4.7 Impulse line size .................................................................................................................................. 5

4.8 Insulation ............................................................................................................................................. 6

5 Horizontal piping installations ........................................................................................................... 6

5.1 Gases .................................................................................................................................................... 6

5.2 Liquids .................................................................................................................................................. 6

5.3 Condensing vapours, e.g. steam ....................................................................................................... 7

6 Vertical piping systems ....................................................................................................................... 7

6.1 General ................................................................................................................................................. 7

6.2 Gases .................................................................................................................................................... 7

6.3 Liquids .................................................................................................................................................. 7

6.4 Condensing vapours, e.g. steam ....................................................................................................... 8

7 Piezometer ring .................................................................................................................................... 8

8 Special cases ....................................................................................................................................... 8

Annex A (informative) Guidance on pipe diameters for long impulse lines ......................................... 10

Annex B (informative) Impulse-line dynamics ......................................................................................... 11

Annex C (informative) Elevation head example calculation ................................................................... 12

Annex D (informative) Supplementary figures ......................................................................................... 13

Bibliography ............................................................................................................................................... 20

ISO 2007 – All rights reserved iii
---------------------- Page: 3 ----------------------
ISO 2186:2007(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 2186 was prepared by Technical Committee ISO/TC 30, Measurement of fluid flow in closed conduits,

Subcommittee SC 2, Pressure differential devices.

This second edition cancels and replaces the first edition (ISO 2186:1973), which has been technically revised.

iv ISO 2007 – All rights reserved
---------------------- Page: 4 ----------------------
ISO 2186:2007(E)
Introduction
The primary devices are flow meters described in ISO 5167 (all parts).

A secondary device in this context receives a differential pressure signal from a primary device and can display

the differential pressure value and convert it into a signal of a different nature, i.e. an analogue or digital signal,

to transmit the value of the differential pressure to another location.
ISO 2007 – All rights reserved v
---------------------- Page: 5 ----------------------
---------------------- Page: 6 ----------------------
INTERNATIONAL STANDARD ISO 2186:2007(E)
Fluid flow in closed conduits — Connections for pressure signal
transmissions between primary and secondary elements
1Scope

This International Standard sets out provisions for the design, lay-out and installation of a pressure signal

transmission system, whereby a pressure signal from a primary fluid flow device can be transmitted by known

techniques to a secondary device safely and in such a way that the value of the signal is not distorted or

modified.
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 4006, Measurement of fluid flow in closed conduits — Vocabulary and symbols

ISO 5167-1:2003, Measurement of fluid flow by means of pressure differential devices inserted in circular cross-

section conduits running full — Part 1: General principles and requirements

ISO 5167-2, Measurement of fluid flow by means of pressure differential devices inserted in circular cross-

section conduits running full — Part 2: Orifice plates

ISO 5167-3, Measurement of fluid flow by means of pressure differential devices inserted in circular cross-

section conduits running full — Part 3: Nozzles and Venturi nozzles

ISO 5167-4, Measurement of fluid flow by means of pressure differential devices inserted in circular cross-

section conduits running full — Part 4: Venturi tubes
3 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO 4006 and ISO 5167-1 and the

following apply.
3.1
secondary device

device which receives a differential pressure signal from a primary device, may display the differential pressure

value and may convert it into a signal of a different nature, i.e. an analogue or digital signal, to transmit the value

of the differential pressure to another location
4 General principles
4.1 Safe containment

The differential pressure signal shall be transmitted in a safe manner within a pipe or tubing to the secondary

device. This requires that the fluid between the primary and secondary device be safely contained. Safe

containment of the fluid requires conformity to the applicable standards and codes and requires the selection of

the proper materials of construction, the fabrication methods and practices and any required gaskets and

ISO 2007 – All rights reserved 1
---------------------- Page: 7 ----------------------
ISO 2186:2007(E)

sealing materials. For on-line maintenance or verification, design shall cover safe means for proof of isolation,

depressurization, flushing and removal/replacement of secondary instrumentation.
4.2 Piping specification

The pipe or tubing installed between the primary and secondary device should comply with applicable national

standards and codes of practice.
NOTE 1 National regulations can also apply.

A process-piping specification should include the specification for the isolation valve (or block valve) closest to

the primary device. The specification for the piping or tubing between this isolation valve and the secondary

device, including any additional valves in this piping, may differ from the piping specification for the isolation

valve. This is because the small size, and often the more limited temperatures involved on the instrument

secondary piping, justifies these differences.

The break (change) in piping specification between the process and the instrument (or secondary) side is

normally at the process isolation valve on its secondary connection end (see Figure 1). If the process-piping

specification requires flanged connections, then the process end of the isolation valve is flanged and the mating

flange on the secondary side is an instrument connection or may have another approved fitting.

NOTE 2 An approved hydrostatic test can be required for piping systems to prove the integrity of the pressure-containing

parts of the piping system.

NOTE 3 Some installations require provision for “rodding out” of the process connections. This is the use of a rod or other

physical device to remove materials blocking the free flow of fluid in the impulse lines. Safety precautions apply.

Key
1primary side
2 secondary side

3 specification break, where the piping specifications change between secondary and primary

4 conduit running full
5 primary head creating device
6 isolation valves
7 impulse line connecting pipe
8manifold
9 secondary device
10 bleed valves, typical
11 alternative location of equalization valve
Figure 1 — Primary and secondary at same elevation, preferred installation
2 ISO 2007 – All rights reserved
---------------------- Page: 8 ----------------------
ISO 2186:2007(E)
4.3 Isolation (block) valves

Isolation (block) valves are required to separate the entire measurement system from the main pipeline, when

necessary, but they should not affect the pressure signal.

It is recommended that isolating valves should be located immediately following the pressure tappings of the

primary element. If condensation chambers are installed, isolation valves may also be fitted immediately

following the condensation chambers. However, if condensation chambers are used, it is important to check that

they are emptied regularly and that they do not become a source of leaks due to corrosion.

When specifying an isolation valve, practical considerations include the following.

a) The valve shall be rated for the pipe design pressure and temperature.

b) There shall be a careful choice of both valve and packing, particularly in the case of dangerous or corrosive

fluids and with gases such as oxygen.

c) Valves shall be chosen that do not affect the transmission of a pressure signal, particularly when that signal

is subject to any degree of fluctuation.

Ball valves or gate valves should be used where possible, as globe-style block valves can create a pocket of gas

or liquid if they are installed with the valve stem in the vertical plane.

NOTE This pocket can result in a distortion of the pressure difference, which can result in an error in the indicated

measurement. Installation with the valve stem at an angle of 90 from the vertical normally solves this problem.

4.4 Valve manifolds

Valves are often installed to permit operation, calibration and troubleshooting of the secondary device without

removing it. Some typical valve manifold configurations are shown in Figure 2.
These valves are used
a) to isolate the secondary device from the impulse lines;

b) to open a path between the high and low pressure sides of the secondary device. The secondary device

zero (no flow signal) can be adjusted at operating pressure with one block valve closed and the bypass

valve(s) open;

c) to drain or vent the secondary device and/or the impulse piping to the drain or to atmosphere.

Manufactured valve manifolds can reduce cost and save space. Valve manifolds integrate the required valves

and connections into one assembly. Valve manifolds shall be installed in the orientation specified by the

manufacturer to avoid possible errors caused by trapped pockets of gas or liquid in the body.

ISO 2007 – All rights reserved 3
---------------------- Page: 9 ----------------------
ISO 2186:2007(E)
Key
1 secondary instrument
2 manifold block
3 block valve
4 equalizer valve
5 vent, drain and calibration plug
6 vent, drain and calibration valve (optional if dashed)
7 vent, drain and calibration valve
8 process side
Figure 2 — Typical manifold configurations
4.5 Installation

The installation design should minimize the separation between the primary and secondary devices. The

connecting piping is variously referred to as “impulse lines”, “gauge lines”, “instrument tubing” or “instrument

piping”.

The detailed design for the installation of the flow meter secondary system should consider instrument

troubleshooting and calibration. To accurately convey the pressure difference, the instrument lines shall be as

short and direct as possible and the two lines should be the same length.

NOTE 1 For circumstances where the instrument lines are necessarily long, guidance on the preferred line diameter is

given in Annex A. See additionally 4.7.1, 4.7.2 and 4.7.3.

Access to the impulse lines, the valves, the valve manifold and the secondary device is required to enable

maintenance and calibration. Installations providing this access shall not increase measurement uncertainties

by being excessively long with excessive fittings.
4 ISO 2007 – All rights reserved
---------------------- Page: 10 ----------------------
ISO 2186:2007(E)

Any difference in elevation between the primary device pressure taps and the secondary device results in a

pressure difference between the two ends of the impulse lines due to the hydrostatic pressure of the fluid

column in the impulse lines.
NOTE 2 This effect is usually greater for liquids than for gases.

The impulse lines shall be installed in such a way that the hydrostatic pressure in the two impulse lines is

identical. If the fluids in the two lines are not identical in density, a difference in pressure is generated. Density

differences arise when there is a temperature difference between the fluids in the two impulse lines. It is

recommended that, if possible, the two impulse lines be fastened and insulated together, when it is required to

avoid significant temperature differences between them.

NOTE 3 Non-identical fluids in the two impulse lines can also give rise to density differences.

The impulse lines shall be installed so that the slope is in one direction only (upward or downward depending on

the fluid; see Clauses 5 and 6. If a change to the slope direction is unavoidable, then only one such change shall

be made. In this case
...

SLOVENSKI STANDARD
SIST ISO 2186:2010
01-april-2010
3UHWRNWHNRþLQY]DSUWLKNDQDOLK3RYH]DYH]DSUHQRVVLJQDODWODNDPHG
SULPDUQLPLLQVHNXQGDUQLPLHOHPHQWL

Fluid flow in closed conduits - Connections for pressure signal transmissions between

primary and secondary elements

Débit des fluides dans les conduites fermées -- Liaisons pour la transmission du signal

de pression entre les éléments primaires et secondaires
Ta slovenski standard je istoveten z: ISO 2186:2007
ICS:
17.120.10 Pretok v zaprtih vodih Flow in closed conduits
SIST ISO 2186:2010 en

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

---------------------- Page: 1 ----------------------
SIST ISO 2186:2010
---------------------- Page: 2 ----------------------
SIST ISO 2186:2010
INTERNATIONAL ISO
STANDARD 2186
Second edition
2007-03-01
Fluid flow in closed conduits —
Connections for pressure signal
transmissions between primary and
secondary elements
Débit des fluides dans les conduites fermées — Liaisons pour la
transmission du signal de pression entre les éléments primaires et
secondaires
Reference number
ISO 2186:2007(E)
ISO 2007
---------------------- Page: 3 ----------------------
SIST ISO 2186:2010
ISO 2186:2007(E)
PDF disclaimer

This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but shall

not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In

downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat

accepts no liability in this area.
Adobe is a trademark of Adobe Systems Incorporated.

Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation

parameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In the

unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below.

© ISO 2007

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

ISO's member body in the country of the requester.
ISO copyright office
Case postale 56  CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
Web www.iso.org
Published in Switzerland
ii ISO 2007 – All rights reserved
---------------------- Page: 4 ----------------------
SIST ISO 2186:2010
ISO 2186:2007(E)
Contents Page

1 Scope .................................................................................................................................................... 1

2 Normative references .......................................................................................................................... 1

3 Terms and definitions .......................................................................................................................... 1

4 General principles ............................................................................................................................... 1

4.1 Safe containment ................................................................................................................................ 1

4.2 Piping specification ............................................................................................................................ 2

4.3 Isolation (block) valves ....................................................................................................................... 3

4.4 Valve manifolds ................................................................................................................................... 3

4.5 Installation ........................................................................................................................................... 4

4.6 Pressure taps ....................................................................................................................................... 5

4.7 Impulse line size .................................................................................................................................. 5

4.8 Insulation ............................................................................................................................................. 6

5 Horizontal piping installations ........................................................................................................... 6

5.1 Gases .................................................................................................................................................... 6

5.2 Liquids .................................................................................................................................................. 6

5.3 Condensing vapours, e.g. steam ....................................................................................................... 7

6 Vertical piping systems ....................................................................................................................... 7

6.1 General ................................................................................................................................................. 7

6.2 Gases .................................................................................................................................................... 7

6.3 Liquids .................................................................................................................................................. 7

6.4 Condensing vapours, e.g. steam ....................................................................................................... 8

7 Piezometer ring .................................................................................................................................... 8

8 Special cases ....................................................................................................................................... 8

Annex A (informative) Guidance on pipe diameters for long impulse lines ......................................... 10

Annex B (informative) Impulse-line dynamics ......................................................................................... 11

Annex C (informative) Elevation head example calculation ................................................................... 12

Annex D (informative) Supplementary figures ......................................................................................... 13

Bibliography ............................................................................................................................................... 20

ISO 2007 – All rights reserved iii
---------------------- Page: 5 ----------------------
SIST ISO 2186:2010
ISO 2186:2007(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 2186 was prepared by Technical Committee ISO/TC 30, Measurement of fluid flow in closed conduits,

Subcommittee SC 2, Pressure differential devices.

This second edition cancels and replaces the first edition (ISO 2186:1973), which has been technically revised.

iv ISO 2007 – All rights reserved
---------------------- Page: 6 ----------------------
SIST ISO 2186:2010
ISO 2186:2007(E)
Introduction
The primary devices are flow meters described in ISO 5167 (all parts).

A secondary device in this context receives a differential pressure signal from a primary device and can display

the differential pressure value and convert it into a signal of a different nature, i.e. an analogue or digital signal,

to transmit the value of the differential pressure to another location.
ISO 2007 – All rights reserved v
---------------------- Page: 7 ----------------------
SIST ISO 2186:2010
---------------------- Page: 8 ----------------------
SIST ISO 2186:2010
INTERNATIONAL STANDARD ISO 2186:2007(E)
Fluid flow in closed conduits — Connections for pressure signal
transmissions between primary and secondary elements
1Scope

This International Standard sets out provisions for the design, lay-out and installation of a pressure signal

transmission system, whereby a pressure signal from a primary fluid flow device can be transmitted by known

techniques to a secondary device safely and in such a way that the value of the signal is not distorted or

modified.
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 4006, Measurement of fluid flow in closed conduits — Vocabulary and symbols

ISO 5167-1:2003, Measurement of fluid flow by means of pressure differential devices inserted in circular cross-

section conduits running full — Part 1: General principles and requirements

ISO 5167-2, Measurement of fluid flow by means of pressure differential devices inserted in circular cross-

section conduits running full — Part 2: Orifice plates

ISO 5167-3, Measurement of fluid flow by means of pressure differential devices inserted in circular cross-

section conduits running full — Part 3: Nozzles and Venturi nozzles

ISO 5167-4, Measurement of fluid flow by means of pressure differential devices inserted in circular cross-

section conduits running full — Part 4: Venturi tubes
3 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO 4006 and ISO 5167-1 and the

following apply.
3.1
secondary device

device which receives a differential pressure signal from a primary device, may display the differential pressure

value and may convert it into a signal of a different nature, i.e. an analogue or digital signal, to transmit the value

of the differential pressure to another location
4 General principles
4.1 Safe containment

The differential pressure signal shall be transmitted in a safe manner within a pipe or tubing to the secondary

device. This requires that the fluid between the primary and secondary device be safely contained. Safe

containment of the fluid requires conformity to the applicable standards and codes and requires the selection of

the proper materials of construction, the fabrication methods and practices and any required gaskets and

ISO 2007 – All rights reserved 1
---------------------- Page: 9 ----------------------
SIST ISO 2186:2010
ISO 2186:2007(E)

sealing materials. For on-line maintenance or verification, design shall cover safe means for proof of isolation,

depressurization, flushing and removal/replacement of secondary instrumentation.
4.2 Piping specification

The pipe or tubing installed between the primary and secondary device should comply with applicable national

standards and codes of practice.
NOTE 1 National regulations can also apply.

A process-piping specification should include the specification for the isolation valve (or block valve) closest to

the primary device. The specification for the piping or tubing between this isolation valve and the secondary

device, including any additional valves in this piping, may differ from the piping specification for the isolation

valve. This is because the small size, and often the more limited temperatures involved on the instrument

secondary piping, justifies these differences.

The break (change) in piping specification between the process and the instrument (or secondary) side is

normally at the process isolation valve on its secondary connection end (see Figure 1). If the process-piping

specification requires flanged connections, then the process end of the isolation valve is flanged and the mating

flange on the secondary side is an instrument connection or may have another approved fitting.

NOTE 2 An approved hydrostatic test can be required for piping systems to prove the integrity of the pressure-containing

parts of the piping system.

NOTE 3 Some installations require provision for “rodding out” of the process connections. This is the use of a rod or other

physical device to remove materials blocking the free flow of fluid in the impulse lines. Safety precautions apply.

Key
1primary side
2 secondary side

3 specification break, where the piping specifications change between secondary and primary

4 conduit running full
5 primary head creating device
6 isolation valves
7 impulse line connecting pipe
8manifold
9 secondary device
10 bleed valves, typical
11 alternative location of equalization valve
Figure 1 — Primary and secondary at same elevation, preferred installation
2 ISO 2007 – All rights reserved
---------------------- Page: 10 ----------------------
SIST ISO 2186:2010
ISO 2186:2007(E)
4.3 Isolation (block) valves

Isolation (block) valves are required to separate the entire measurement system from the main pipeline, when

necessary, but they should not affect the pressure signal.

It is recommended that isolating valves should be located immediately following the pressure tappings of the

primary element. If condensation chambers are installed, isolation valves may also be fitted immediately

following the condensation chambers. However, if condensation chambers are used, it is important to check that

they are emptied regularly and that they do not become a source of leaks due to corrosion.

When specifying an isolation valve, practical considerations include the following.

a) The valve shall be rated for the pipe design pressure and temperature.

b) There shall be a careful choice of both valve and packing, particularly in the case of dangerous or corrosive

fluids and with gases such as oxygen.

c) Valves shall be chosen that do not affect the transmission of a pressure signal, particularly when that signal

is subject to any degree of fluctuation.

Ball valves or gate valves should be used where possible, as globe-style block valves can create a pocket of gas

or liquid if they are installed with the valve stem in the vertical plane.

NOTE This pocket can result in a distortion of the pressure difference, which can result in an error in the indicated

measurement. Installation with the valve stem at an angle of 90 from the vertical normally solves this problem.

4.4 Valve manifolds

Valves are often installed to permit operation, calibration and troubleshooting of the secondary device without

removing it. Some typical valve manifold configurations are shown in Figure 2.
These valves are used
a) to isolate the secondary device from the impulse lines;

b) to open a path between the high and low pressure sides of the secondary device. The secondary device

zero (no flow signal) can be adjusted at operating pressure with one block valve closed and the bypass

valve(s) open;

c) to drain or vent the secondary device and/or the impulse piping to the drain or to atmosphere.

Manufactured valve manifolds can reduce cost and save space. Valve manifolds integrate the required valves

and connections into one assembly. Valve manifolds shall be installed in the orientation specified by the

manufacturer to avoid possible errors caused by trapped pockets of gas or liquid in the body.

ISO 2007 – All rights reserved 3
---------------------- Page: 11 ----------------------
SIST ISO 2186:2010
ISO 2186:2007(E)
Key
1 secondary instrument
2 manifold block
3 block valve
4 equalizer valve
5 vent, drain and calibration plug
6 vent, drain and calibration valve (optional if dashed)
7 vent, drain and calibration valve
8 process side
Figure 2 — Typical manifold configurations
4.5 Installation

The installation design should minimize the separation between the primary and secondary devices. The

connecting piping is variously referred to as “impulse lines”, “gauge lines”, “instrument tubing” or “instrument

piping”.

The detailed design for the installation of the flow meter secondary system should consider instrument

troubleshooting and calibration. To accurately convey the pressure difference, the instrument lines shall be as

short and direct as possible and the two lines should be the same length.

NOTE 1 For circumstances where the instrument lines are necessarily long, guidance on the preferred line diameter is

given in Annex A. See additionally 4.7.1, 4.7.2 and 4.7.3.

Access to the impulse lines, the valves, the valve manifold and the secondary device is required to enable

maintenance and calibration. Installations providing this access shall not increase measurement uncertainties

by being excessively long with excessive fittings.
4 ISO 2007 – All rights reserved
---------------------- Page: 12 ----------------------
SIST ISO 2186:2010
ISO 2186:2007(E)

Any difference in elevation between the primary device pressure taps and the secondary device results in a

pressure difference between the two ends of the impulse lines due to the hydrostatic pressure of the fluid

column in the impulse lines.
NOTE 2 This effect is usually greater for liquids than for gases.

The impulse lines shall be installed in such a way that the hydrostatic pressure in the two impulse lines is

identical. If the fluids in the two lines are not identical in density, a difference in pressure is generated. Density

differences arise when there is a temperature difference between the fluids in the two impulse lines. It is

recommended that, if possible, the two impulse
...

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