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2186-73

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4851903 0009802 6

I

INTERNATIONAL ORGANIZATION FOR STANDARDIZATION .ME>KAYHAPOAHAJ1 oprAHIOAUHJI no CfAHAAPTM3AURH .ORGANISATION INTERNATIONALE DE NORMALISATION

Fluid flow in closed conduits Connections for pressure

signal transmissions between primary and secondary elements

First edition - 1973-03 ..01

..'

w. . . . . . . . UDC 681.121.84: 532.57 Ref. No. ISO 2186-1973 (E)Mf'm~

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Descriptors: flow, pipeflow, flow measurement, pressure measurement, signals, transmission.

•

price based on 34 pages..,.

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2186-73

FOREWORD

ISO (the I nternational Organization for Standardization) is a worldwide federation

of national standards institutes (ISO Member Bodies). The work of developing

International Standards is carried out through ISO Technical Committees. Every

Member Body interested in a subject for which a Technical Committee has been set

up has the right to be represented on that Committee. International organ izations.

governmental an d non-governmental, in liaison with ISO, also take part in the work.

Draft International Standards adopted by the Technical Committees are circulated

to the Member Bodies for approval before their acceptance as International

Standards by the lSO Council.

International Standard ISO 2 18 6 was drawn up by Technical Com m ittee

ISO/TC 30, Measurement of fluid flow in closed conduits.

It was approved in April 1971 by the Member Bodies of the following countries:

Austria

Belgium

Chile

Czechoslovak ia

France

Germany

Greece

Hungary

India

Italy

Japan

Korea, Rep. of

Netherlands

Poland

Portugal

South Africa, Rep. of

Spain

SwitzerlandUnited Kingdom

U~S.AI

U ~ S . S . R .

No Member Body expressed disapproval of the document.

© International Organization for Standardization. 1973 •

Printed in Switzerland

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4851903 0009803 8

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r --.

INTERNATIONAL STANDARD ISO 2186-1973 (E)

4851903 0009804 0186-73

Fluid flow in closed conduits -- Connections for pressure

signal transmissions between primary and secondary elements

o INTRODUCTION 4 PRESSURE TAPS

This I nternationa I Standard relates to the types of pressure

difference primary elements fo r flow measurement /

described in ISO /R 541 and ISO /R 781. 4.1 Location of pressure taps in horizontal pipes

T he fo llo win g positions of th e wall pressure taps on the

straight cy lindrical pipe are recommended:

1 ) Gas: in the vertical m eridian plane, upwards (see

Notes 1 an d 2),

The chosen order of presentation follows a logical

progression away from the origin of the pressure signal

obtained from the primary element, through to the inlet of

the secondary device.

It should be noted that in th is c on te xt a secondary device is

defined as a device receiving a differential pressure signal

from a primary element and converting it, when necessary

with the assistance of auxiliary power, into a signal of a

different nature,

2) Liquids: in a m eridian plane with which th e

horizontal meridian plane is forming an angle not greater

than 45° above or below according with the position of

th e secondary device (see Note 4).

3) Steam: in the h ori zo nta l m e ri dian plane.Methods of grouping the individual un its are presented in a

section that shows various types of i ns ta lla ti on la yo uts .

NOTES•. . . .

1 SCOPE 1 The position of dry gas taps may be varied without risk from the

position indicated in 4.1.

This International Standard describes means whereby apressure signal from a prim ary elem ent can be transmitted

by known techniques to a secondary device in such a way

that the value of the signal is not distorted or modified even

though it m ay be changed into a signal of a different

nature.

2 The position of wet gas taps should be vertical if possible to

allow draining to occur. They should therefore be less than 45° off

the vertical meridian plane.

3 In the case of gently sloping pipelines, l .e . the slope of which can

be considered as negligibl 8, it is often possi ble to maintai n the taps

on a horizontal plane by varying their individual positions relative to

the pipe centre- line. It is par ticularly desirable that the taps are on a

horizontal plane when hot l iquid flow is to be measured with a v ie w

to avoiding corrections for altitude.2 FIELD OF APPLICATION

T his International Standard is concerned only with the

pressure difference techniques of flow m easurem ent. It

does not consider the characteristics of th e se co nd ary

d ev ice s, an d it does not include transducers or other similar

instruments. Electrical tran sm issio n te ch niq ue s are no t

dealt with in this International Standard. Pressuretransducers and m icrodisplacem ent secondary devices will

be the subject of a separate International Standard.

4 Care should be ta ken when using for Iiquids, a position in the

horizontal meridian plane. If the liqu id is clean it is advisable to

avoid the risk of gas in the pressure l ines by using a tap location

below the pipe horizontal meridian plane. If, on the other hand, the

liqu id has a signif icant solid content, then a position above the

horizontal centre-I ine is recommended. In neither case should thetaps be more than 45° from the horizontal. The Case where there is

a considerable volume of gas in a liquid line is exceptional, and

needs special consideration: a horizontal tap position shou ld be

used in conju netion with pipe gas vents and gas collecting chambers

in th e p re ssu re lines (see section 11).

3 REFERENCES

ISO/R 541, Measurement of fluid flow by means of oritice

plates and nozzles. 4.2 Location of pressure taps in vertical pipes ..

In th e case of vertical pipes there are generally no problems

as far as th e rad ial P ositio n O f p re ssu re tap s is co nce rn ed .

ISO/R 781, Measurement of fluid flow by means of Venturi

tubes.

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2186-73 4851903 0009805 1

4.3 Pressure taps and connections

Shape, d iam eter, length and location of pressure taps

should be in accordance with ISO/R 541, clause 6.2; note

shou Id be taken in particular of su b-clauses 6.2.1 .2 and

6~2.1.6~

pressure piping between the p ressu re taps an d th e valve , th is

latter diam eter rem aining unchanged as well over its whole

length.

The valve shou ld be of full b ore v alv e type in order:

The re should be no burrs o f o ther irregularities on the

inside o f th e pipe at the connections or along th e edge of

th e hole through the pi pe wall . In no case shall an y fittings

project beyond the inner surface o f th e pipe wall. C le ar ly

where there is risk of solid or liqu id blockage it is advisable

to use a l ar ge t ap p in g size w ith in the lim its g iven .

1) in th e case of Iiqu id f low, to avoid trapping ga s

bubbles in the va lve structure ;

2) in the case of gas flow, to av o id t ra pp i ng Iiqu id inth e v alv e stru ctu re .

6 CONDENSATION CHAMBERS

4.4 Practical requ irementsThe modern t rend in secondary device design is toward th e

micro-displacement type o f d i ff e re n ti a l pressure u nit. T here

are , h ow ev er, still a range of instruments widely used

th roughou t the world th at have a capacity comparable to,

but sma l le r than, th e popular m ercu ry U -tube type of

device.

Som e typical arrangem ents fo r pressu re taps are g iven in

Figure 1, but it shou Id be noted that th e in form ation is

included fo r general gu i da n ee only.

5 ISOLATING VALVES

It is therefore necessary to consider variations in th e

capacitv o f condensation cham bers , bu t it is notr e commended that they shou ld be entirely omitted, even

when m i c ro -d is pl ac eme n t secondary devices are used ..1 Isolating valves are needed to separate the entire

m easurem ent system from the m ain pipeline when

necessary, bu t th ey shou ld not affect the p re ss ur e s ig na l.

It is r e commended that isolating va lves should be located

immedia te ly following th e primary e lemen t . If

co ndensatio n cham bers are installed the iso lating valves

may be fitted immedia te ly following th e c on de nsa tio n

chambers (see Figu re 18).

Practical considerations include:

It is suggested that excep t when used with

micro-displacement dev ices, th e shape of th e condensation

chamber should be as shown in Figure 2. Fo r

m icro-d isp lacem en t devices, the condensation chambers

m ay take the fo rm o f sho rt leng th s o f unlagged p ipe

between the pressu re taps and the isolating valves.

The capacities of th e condensation chambers shown in

Tab le 1 can be relate d both to secondary device max imum

displacement at maximum head as well as to steam

conditions, as shown in F igu re 3. Generally, it is a dv isa ble

to use condensation cham bers th at have a capacity two to

three tim es that o f th e secondary device displacement,

particu larly when it is known o r suspected th at large and

sudden variations in th e flo w rate m ay occur.

•he final choice both of th e valve specification and its

lo cation is left to th e instrument eng ineer and /o r u ser. T he

recommendat ions given here are therefo re sub ject to

alteration s w hich m ay b e n ec es sa ry in view of the operating

conditions and the nature of the fluid.

1) the insta lla tio ns o f valves suited to the pipe pressure ;In th e case of very h ig h p re ss u re /t em p e ra tu re steam, it is

advisable to use a catchpo t of approximately the s ame

vo l ume as the condensation cham ber, to protect the

primary e lemen t from damage caused by cool liquid from

the pressure piping re tu rn ing through the primary e lement

as a result of a large an d sudden change in flow rate. An

example of arrangem ent is given on Figu re 26.

The connecting p ipe between th e primary element an d

condensation cham ber/catchpot shou ld be e ither o f the

s ame materia l as t he p ip el in e, or o f e qu iv a le nt specification.

2) careful choice of both valve an d packing,

particularly in the case of corrosive o r d an ge ro us fluids,

and w ith su ch gases as oxygen ;

3) th e need to use valves whose design does no t affect

th e t ransmission of a p re ss ure sig na l, p artic ula rly when

th at s ignal is subject to an y degree o f fluctuation orpulsation.

5.2 Valve passages

It is r ecommended that th e genera ' rem arks about

constancy of diameter given in section 10 shou ld be u sed as

a gu ide in th is section as well. T hus, every a t tempt shou Id

be made to ensu re in th e case where the valva is

immed ia te ly adjacent to th e pressure tap that th e in te rn al

diameter of valve connections and the minimum passage

diameter inside the valve shou ld keep a constant value an d

preferably not be less than the internal diameter o f th e

In th e case of primary elem ents and condensation chambers

in sta lled in vertical m ains, it is necessary to have bo th

condensation cham bers installed on the same level,

preferably that o f th e higher tap, and lagged as shown in..

F igure 20 for exam ple . T he bo re o f the connecting pipe

shou ld be large enough to avo id an y risk of blockage an d

secondary device response lag, and the pipe itself shou Id be

lagged.

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2186-7~ 4851903 0009806 3

ISO 2186-1973 (E)---- -------~~

For threaded connection

Before weldingAfter u ve ld in g a nd boring

Centeri ng pin --f r- Centering hole < p < d ~

/

•

For welded connection

After welding and boring

Centeringpin-

d

Flanged adaptor for low to medium

pressure/temperature steam installation

Carefully remove

the burrs, radius ~ 0, 1 d

I

I

Carefully remove

the burrs, radius ~ 0, 1 d..

Threaded adaptor ->

Flanged valva=->

Condensation chamber ----------

FIGURE 1 - TYPiCalarrangements for pressure taps

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ISO 2186 ..1973 (E)2186-73 4851903 0009807 5

The protruding part~-....--

is optional00 mm

,.-.InletEEC). .00C O

- e -

Type A

at inlet and outlet

screwed ends

t- E1: l E

oo

Outlet~

I

Type B Type C• •

at inlet welding end -+ - - - at inlet and outlet ~+- .. ...

and at outlet screwed end welding ends I

"fl- t-

~ ~

I

I•

Side view shown,

other dimensions

a s fo r Type A

Side view shown,

other dimansions

as for Type A

NOTE - The pipe ends can also be fitted with flanges.

FIGURE 2 - Condensation chamber characteristics, types A, Band C

TAS LE 1 - Condensation chamber dimensions

Inlet d1 Outlet d2Test

pressureapacityshreaded Welded Threaded Welded

T end en d end endy~~--------~----------~~--------~----------~--~--~~--~----------~--------~ize

bar *m3In mm mm mmm mm

A 1/ 2 1 /2

1 B 8001,3 8,7 230 5/2 -

c 21,3 21,3190

1/2 1/2

2 25021,3 8,7 100 5/2 i

c 21,3 21,3-

5/8 5/8

3 B 7004 5/8 230 7,1

c 24 24-320

5/8 5/8 -

4 5/8 2204 100 7, 1-

c 24 24

600230 12,584 24-540

24c 100 12,5 1704 : ' -.

...1 bar = 105 Pa

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2186-73 4851903 0009809 9

/

is important that su fficient clearance shou ld be available

beneath the vesse l to a l low access to th e drain valve.In the case of gases, se ttling cham bers are advisable when

th e m e asu re d flu id is both dirty and/or wet.

Settling cham bers m ay be fou nd u sefu l for steam

installations where pressure pipe scaling c an d ev elo p. The v alve sh ou ld preferably be a fu ll bore type so that it

can be cleaned an d probed if blockage is suspected, or if the

cham ber is heavily en cru sted w ith d ep osits.

It should also be noted that pressu re holes, pressure pipe

bores, an d the connections to the settling chamber s should

be large r fo r very dirty liqu ids and gases.

The capacity of the settl ing chambers shou Id be as large as

practically possible or as large as the needs of the

installation demand. The proportions given in Figure 5 are

typical and should be sufficient for most purposes.

However , the frequency of maintenance and th e degree of

so lid and/o r condensation entrainm ent are matte rs that

shou Id decide the size of settl ing chamber to u se.

7.2.2 Description of the technique

In all cases the settling cham bers shou ld be located at th elowest point of the pipe run.

If th e secondary device is above the prim ary elem ent it is

advisable to include gas collecting cham bers in the pressure

piping system as well as settling chambers in the case of

Ilqu id ftow.

7.2.3 Drawings and dimensional data

A typical design of settling cham ber is shown in Figu re 5 . It

Hole su itable for _ _

fix in9 boIts

. ,Venting i

. . . . . . .-

A

tI L

Valves _/

" 1 : _N

FIGU RE 4 - Arrangement of wall mounted gas collecting chambers and valves

-- -- . - ----

6 ..., ._ ... ...

~. From primary-

element To secondary

device

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To secondary device

1

2186-73 4851903 0009810 5-

..

From primary element pressure tap

Venting

Plunging tube

/ •

..-.....---Drain cock

{

l

FIGURE 5 - Settling Chamber

ISO 2186-1973 (E)

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ISO2186-1973 (E)-------

4851903 0009811 7186-73

8 SPECIAL TECHNIQUES USED AS PROTECTION

AGAINST VERY COLD AMBIENT CONDITIONS

The interface between the m etered and the seal ing fluids

should be at exactly the s ame level in both sealing chambers

wh en th ere is no flow.In th e caseswhere pressure pipes con tain w ater i t i s p os sib le

to protect th em a ga in st frost by the use of heating elem ents

such as electrical tapes or steam coils.

The filling level is determined by m eans of purge valves and

w he re po ssible it i s des ir ab le to in sta ll v is ua l means which

allow co nstant co ntro l of t he in te rf ac e.

The exact use of these techniques depends on the particular

location, and advice cannot be generalized. It i s impor ta n t

to ensure that th e heating is controlled, uniform, an d of

equal amoun t to each pressure pipe and an y au xiliary u nit

included in the pipe run. W here po ssible the p re ssu re p ip es

should be run and lagged together, but care shou Id be taken

not to overheat l iquids in the pipes since this m ay cause

vaporization.

The sealing flu id fills the pressure pipes between the seal ingcham ber and the m eter.

For guidance, suitable sealing chamber dimensions for

industrial m eters are about 100 mm diam eter and 250 to

300 mm long.

It may be noted that the same techniques are useful when

warm or hot viscous flu ids are metered, to prevent

coagu lation or blockage in cold pressure pipes and an y

other n arrow p ass ag es.

W here m icro-displacem ent devices are used the sealing

cham ber can be elim inated or replaced by a pipe.

In all cases, the seal i ng cham ber capacity should be larger

than the m axim um volum e of m easuring liqu id displaced in

the m eter. W hen designing sealing chambers it should be

carefullv checked that their inside diam eters rem ain

constant over t he e ff ec ti ve w ork in g are a.9 SEALING CHAMBERS AND PURGE SYSTEMS

9.1 Sealing chambe rs

The m eter read ing shou ld be corrected to take account of

the displacement of the (s ea lin g flu id /m e te re d fluid)

interface in th e sealing chamber .

9.1.1 Sealing chambers without partition

Seal ing chambers containing a liqu id which separates th e

metered flu id from the fluid in th e m eter m ay be em ployed

where:

This correction will be of g re ate st im p orta nc e when th e

difference in density is greatest between th e se alin g and

m etered fluids. W hen m icro-displacem ent devices are used

this correction is negligible.

- the m etered flu id is corrosive;M ethod by which differen tial p ressure m ay be calculated

when seal ing cham bers are used with a U-tube type of

m eter is given in Annex A.the m etered fluid is Iikelv to congeal, freeze or

condense in the connecting pipes;

- the metered fluid i s v er y viscous;

- deposits are likely to occur in the connecting pipes

or in the meter, etc.

9.1.2 Sealing chambers with partitions

W hen the physical and chem ical characteristics of th e

metered fluid ar e such that a su itable sealing fluid cannot

be found, se alin g ch am b ers w ith p artitio ns m ay be used.It m ust, however, not be forgotten that the pipes

connecting pressure taps and seal ing chambers wilt no t be

protected by th e use of a seal ing flu id.

The sealing fluid should not mix or react with th e m e te re d

fluid or th e manomet r ic fluid an d shou ld differ in density

from both fluids by an am o unt sufficient to ensure a stable

interface.

Diaphragm an d bellows units are the simplest form of

partition generally used.

It is necessary to ensure that both sealing cham bers have

the s am e s tre ss /d is pla cem en t c ha ra cte ris tic .

Sealing chambers should be installed at the sam e level an d

as close as possible to th e pressure taps. When there is a risk

of congealing , freezing or condensation of the m etered

fluid, the connections from the pressure taps shou ld be

included in a pocket with the pipe lagging or be provided

with supplementary h ea tin g. T his m ight be provided as well

fo r s ea lin g c ham be rs , if they a re em plo ye d for Iiquefiabte

fluid flow measurements .

The volum etric displacem ent of th e sealing fluid over th e

full scale range of the m eter should be greater than th emax imum volume displaced by th e mete r itself.

G as v en tin g systems shou Id be used on both sides of the

partition.

The general arrangem ents of sealing cham bers ar e shown in

F igu res 6 an d 7.

~n general the rem arks in 9 .1 .1 applv equally to sealing

chambers with partition.

In the cases where sealing chambers with partition are used

it is normal for the m anufacturer o f such units to provide

the relatio nship between input an d output signals.

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-~~------ ISO 2186-1973 (E)2186-73 4851903 0009812 9

~- Metered fluid

F IGURE 6 - Sealing cham bers - Metered fluid heavier th an sea ling flu id

;' Sealing fluid

..

FIGURE 7 - Seal ing chambers - Metered f luid lighter than sealing fluid

9.1.3 Sealing liquids

Some typical sealing l iquids are given in Table 2.

TABLE 2 - Properties of sealing liquids

Density

at the Freezing Boiling-

temperature temperature temperatureKind of liquid

20°C

kg/m3 °c °c

-

Glycer ine 1 262 -- 17 290.

Mixture of water

and glycer i ne 1 130 -22,5 106

(Volume 1 : 1)

Dibutvl phthalate 1 047~

35 340. . . . . _ _ .

Ethy l alcohol 789 -112 78

Ethylene glycol 1 113 -12 197

Mi xture of water

an d ethylene glycol 1 070 - 36 110

(Volume 1 : 1)

9.2 Purge system

9.2.1 General

These techniques are intended to prevent dirty or

d an ge ro us flu id s from entering the pressure pipes an d the

secondary devices, and they are, to some extent, an

alternative to both settling chambers and sealing chambers.

Generally, there ar e three ways in which purges m ay be

used:

1) the introdu ctio n of gas in to pressure

containing gases;

2) the introduction

containing liquids:

of gas into pressu re•

Pipes

~- .. - . ... 22 2 2 2C

.r

9

. J W z= w e .. _ .. . . .

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ISO 2186 ..1973 (E)4851903 0009813 0186-73

3) the introduction of Iiqu id into pressu re

containing liquids;

..

pipes 9.2.3 Introduction of gas into pressure pipes containing

liquids

The rate of purge will depend on :

- whethe r the m easured flow is steady;

- the type of secondary device used;

- the total capacity of the pressure pip e ru ns.

It should be em phasized that in practice care should be

taken to ensure that the purge does not influence th e

performance of th e secondary dev ice nor the fluid

temperature equilibrium between th e tw o pressu re pipes .

In div idu al d eta ils are given in th e f ollowi ng clauses.

The same general commen ts apply as given in 9.2.2, bu t

there are im portan t facts to note.

Gas purge into liquid filled pressure pipes can cause

difficulty an d error if the metered flow is unsteady, if small

differential p ressures are used , an d if gas vessels ar eincluded in the pressure pipe system.

Furtherm ore, the considerable difference between the

ki nematic v iscosi t ies of the gas and the Ilqu id , as well as

surface tension effects, make abrupt variations in flow rate

or pressure m ore difficult to counter and there is a real

chance that, temporar i ly, the metered fluid will enter the

pressure pipes and cause spurious differential pressure

signals.

9.2..2 Introduction of gas into pressure pipes containing

gas

This technique is advantageous in cases where there is a low

pipel ine pressu re , and the seco nd ary dev ice is lo cated abo ve

the pipeline.

It is also important to note that with this system the

secondary device is operating with gas although it is

concerned with Iiq u id flow, an d therefore, that the

secondary device has a dry calibration relationship between

differential head and flow. It also is important that

Iiquid/gas discontinuities in the pipe system shou Id occur at

the same levels.

If th e flow rate varies with tim e to a considerable extent I

and the m agnitude of variation is large, then it is best to use

a purge flow rate equ iva lent to the m eter to tal capacity

between zero and m axim um displacem ent in o ne m inu te,

Steady flows do not need such a high purge flow, but very

small purge rates should be avoided because they are

difficu It to control ~

Equally , th e use of larger purge flows w ill m ean that special

care will have to be taken to avoid an out-af-balance of

pressure in the pressure piping. It would, for example, mean

that pressure taps and pressure bores shou ld be large

enough to avo id pressu re losses created by a large pu rge

flow. For the s ame reasons it is always necessary to avoid

changes of cross-sectional area at any point in th e p re ss ur e

p ipe system when purge techniques ar e used. Furthermore,

both the high and low pressure m e te r c on ne ctio ns should

be of the sam e length and have the s ame num ber of fittings.

In the case of long pressure piping, it may b e n ec es sa ry to

place a pipe in which the purge fluid would flow up to th e

pressure tap and a second pipe, transm itting th e pressure, to

the secondary device, w ith ou t pressu re drop effect.

In order to keep the purge flow rates equal in both pressure

pipes it is recommended that small variable-area m eters or

sight glasses be included in the purge system. They shou Id

be located at a point between the purge co ntrol valve and

th e point at which th e purge flow enters the pressure pipes,

It is of course necessary to use g as p urg e pressu res that ar e

well above the pi pel ine pressure. Control of purge rate is

usually obtained by means of some type of needle valve or

a simple purge flow regulator.

Figures 8 and 9 show two examples of purge system

installations.

9..2.4 Introduction of liquid into pressure pipes containing

liquids

A liquid purge is usefu l when m easuring effluents or

sewage: in these cases a supply of clean water at the

appropriate pressure will be sufficient. The previous

remarks in this sectio n still apply I except that there are no

density Isurface-tension problems. The purge flow rate can

be decided on the sam e basis as before, but it will be

necessary to reduce th e p ressu re lo sses by using larger bore

pressu re pip es than those su itable fo r gases.

If the l iquids are viscous or have other chem ical properties

that prevent the use of clean water, then care shou Id be

taken to choose a su itable purge fl u id .

If a so urce of potable water is being used to supply a liquid

p urg e, p ositiv e provision must be m ade to avoid back flow

into the potable sys tem.

9.3 Probe units

Often the purge system s described in this International

S tan dard can no t entire ly prevent blockage of th e pressure

taps themselves. In cases w here measurements of flu ids with

entra ined sol ids are requ ired, it is recommended that probe

units should be supplied as part of the purge installation.

Descriptions of typical probe units are g iven in Annex B.

- - - ---- -_ _ --

10...

. . . .

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ISO 2186-1973 (E)2186-73 4851903 0009814 2

Purge supply

-

)J ~

JIIl

\t

1 ~

J,

FIGURE 8 - Example of purge system installation

• E E E EI I W II ' : := = Cooz .

~ '--- -- - -

..--

u:tQJ

C..--

Purge supply

Q)IJ)

'-: : : J

a.C)

co_J

Purge flow control+ indicator

•

FIGURE 9 - Example of purge system installation

in the case of long pressure piping

11

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ISO2186-1973 (E)

2186-73 4851903 0009815 4

10 PRESSURE PIPING 11 INSTALLATION

The mete r should be located close to the prim ary elem ent;

the speed of reponse is reduced if there is a long run. If

possible the distance of transmission by pressure pipi ng

should no t be greater than 16 m beyond which l imit

electrical/pneumatic transm ission shou ld be used. The two

pressure pipes should be kept close together to avoid a falsepressu re difference arising from a difference in temperature.

Where there is any risk of heating or cooling of th e pressure

pipes they should be lagged together . The bores of th e

pressure pipes shou ld be the same an d not sm aller than

6 mm even with "clean" fluids an d non-corrodible piping,

owing to the chance of blockage after long service. If

condensation is Iikelv to occur or if gas bubbles are likely

to be liberated, th e bore shou Id be not smaller than 10 mm .

The arrangement of piping and units compris ing

transmission systems between primary an d secondary

elements , is given in this section.

11.1 Arrangement of valves

The arrangement of valves associated with the secondary

device tends to vary with individual o rg aniz atio ns an d with

appl icatio ns.

The installation should include

a) valves in the high an d low pressure p ip in g a dja ce nt to

the inlet connections of the secondary device;

The ru n of pressure pipes shou ld be arranged so that their

s lope is alw ay s greater than 1 in 12 in order that an y gas

bubbles may rise to the vents an d so that condensed liquidsor solid deposits m ay drain into th e catchpots or water

seals. The slope should b e in crea sed if th e liquid in the

pressure pipes is more viscous than water. In the case of

long runs (for example 30 rn) or where obstructions have to

be avo id ed, th e pressure pipes m ay be run in a series of

slopes provided that gas vents are fitted at all h ig h po in ts,

o r sea lin g c ham b ers at all low points, as appropriate.

b) a valve (often called an equalizing valve) that enables

an y pressure difference that may exist between the high

an d low p ressu re bra nc hes of the system to b e r es ol ve d.

Somet imes , th e isolating valves at th e prim ary elem ent serve

as those genera Ily placed at the inlet c on n ec ti on to th e

secondary device.

Normally, there are also valves th at control the venting of

the meter system.

When long runs cannot be avoided, experience has shown

that the data given in Table 3 are satisfactory and other

recommendations given by various national bodies and

organizations vary only marginally .

One commonly used arrangement of these vario us valves is

that shown in Figures 10 to 25. However, it should be

noted that, in certain cases, an arrangem ent as shown on

the inset of page 14 is used; this arrangement presents the

advantage of making possible the im m ediate detectio n of

any leak.

Further details about pressure piping can be noted from the

various installation d ia gra m s a pp earin g in section 11, and

also in Figures 27 an d 28.

11.2 Arrangement of pressure piping

Exam ples of arrangement of pressure piping (with their

accessories) and pressure taps, up to the secondary device,

are shown in Figures 10 to 27.

12 - -

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--------___._.,----- -------- -- - - ---------

2186-73

TAB LE 3 - Internal diameter of pressure pipe

Values in millimetres

Type of metered fluid

25

Pressure signal

transmission distance

o to 16m 16 to 45 m 45 to 90 m

Water IsteamDry air/gas

Wet ai r or gas

(l.e, risk of

condensation in pipes)

Oils of low to

med ium viscosity

10to 9 13

13 13 13

13 19 25

Very dirty liquids

or gases385

........-~ a--- -- - --- ••p c - - -

4851903 0009816 6ISO 2186-1973 (E)

TABLE 4 - Applications1)

Figure No.

10

11

12

13

14

15

16

17

18

19

24

27

20 Meter below pressure taps;

vertical main

21 Meter below pipe line

22 Mete r below pipe line

- (a lternative arrangement)

23 Meter above pipe line

25 a) and b) Meter above pressure taps;

vertical main

(a l ternative arrangements)

26 Typical ar r angemen t

for either horizontal

or ve rti cal main

Descriptionpplication

Clean liquids

Dry clean gas

Steam and dry

condensable gas

Clean wet gas

High temperature,

high pressure

steam

Meter below pi pe line

Meter above pipeline;

cold liquids

Vertical main; hot liquids

Meter above pipe line

Meter below pipe line

Meter above pressure taps;

vertical main

Meter below pressure taps;

vertical mai n

Meter below pipe tine

Meter below pi pe line,

(alternative arrangement)

Meter above pipe line

Meter below pressure taps;

vertical main

..•

Alternative ar r angemen t

for either horizontal

or vertical main

1) These arrangements are typical; the pri nci pies underlying them

m ay be used for any arrangement of pressure taps, for both

horizontal and vertical pipe lines and for meters above or below the

prim ary e le m en t.

13

. . . .

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ISO 2186-1973 (E) ---_.--~~~----

2186-73 4851903 0009817 8

Clean liquid

Alternative a rrangement of mani fo ld ,

..,....__ppl icable to Figures 10 to 25 as

\f\'811as 28 and 29

Gas collecting .-...

chambe r

I

FIGURE 10- Meter below pipe line

II

II

FIGURE 11 - Meter above Pipe line; COld liquids

~ -- . . . . -- - - -

14 oil

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~ _ _ & a & _ . 7__:a _ _ S _

•

2186-73 4851903 0009818 0

Cleanliquid

.................-- Cooling chamber

I

I :""

r

. . . .

FIGURE 12 - Vertical main; hot liquids

ISO 2186-1973 (E)

•

15

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ISO2186-1973 (E)

16

Clean dry gas

FIGURE 13 - M eter above pipe line

... -- - -- - -

--'".

2186-73 4851903 0009819 1

I

F IGURE 14 - Meter below pipe line

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ISO 2186 ..1973 (E)2186-73

I

II

I

I

I

I

I

•

FIGU RE 15 - Meter above pressure taps; vertical main

........ z - - ... . _ .. ::;zz;z pis •

~ ~ - _ _ . - . . . . . . . . t . - - =

4851903 0009820 8

Clean dry gas

I

I

.....

!

I

..

FIGU RE 16 - Meter belOW pressure taps; vertical main

17

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ISO 2186·1973 (E)2186-7:3

4851903 0009821 0-

Steam and dry condensable gas

.........-- Condensation chamber

..

FIGU RE 17 - Meter below pipe line

FIG URE 18 - Meter below P i PB line (aIternative arrangement'

-- --- - - --- - ----- -- - --- -- -- - --

18. . . . -• ...

-.. ~ .; ~

. . . . .

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ISO 2186-1973 (E)

2186-73 4851903 0009822 1

Steam and dry condensable gas

-[ I

I II II II II II

•

NOTE - The slope of both pressure piping is the same.

•

•

FIGURE 19 - Meter abovePipe line•

I

...- 19

./ - -- -

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ISO 2186 ..1973 (E) ------~----~--

2186-73 4851903 0009823 3

Steam and dry condensable gas

I

,

I

I

FIG URE 20 - Meter below pressure taps; vertical main

20- - - -

-~

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•

2186-73 4851903 0009824 5

Clean wet gas

I

III

II

Settling chamber-

FIGURE 21- Meter below Pipe line

__=-=-=-Z:::~~~F _ e_ -=------=---- .. __ ,_

ISO 2186-1973 (E)

•

21

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--- - -

ISO2186-1973 (E) 2186-73 4851903 0009825 7

C lean wet gas

. . . .

FIGURE 22 - Meter below pipe line (alternative arrangement)

FIGURE 23 - Meter above pipe line

(Figure showinq two alternatives)

-. . . .

22

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2186-73 4851903 0009826 9ISO 2186-1973 (E)

Clean wet ga s

NOTE - The measurement of wet gas in vertical pipes should be discouraged owing to the risk of blockage of pressure taps.

NOTE - The slope of both pressure piping is the same.

I

E

•

I

r

IIIIJI

I •

I ,t

II

I '!-~

..- -

I t- •- . •I • I

I I I

!I riI·t•

f

...tL

tt

•..

FIGU RE 24 -.: Meter below pressure taps; vertical main..

.~ -

-- .._ c . _

_ 2 3

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ISO2186-1973 (E)2186-73

- - ---- -- -----------~-

4851903 0009827 0

Clean wet gas

I

I

I

I

FIG URE 25 a) - Meter above pressu re taps, vertical main (al ternative arrangement)

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2186-73 4851903 0009828 2ISO 2186-1973 (E)------

Clean wet gas

•

I

•

I

NOTE - The slope of both pressure piping is the same.

FIGU RE 25 b) - Meter above pressure taps, vertical main <a lt ernat iv e a rr a ngemen t)

25~ ._ - - __ ._ = _ = .. . __ ..

_. .

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ISO 2186-1973 (E)2186-73 4851903 0009829 4

-. . . .'+-

oCo

3 :o

.-

11

c

" - ; ( > / / /

//~- /"./, "Y, ~ x ;;.:. X )<

» : < : ><> ,,/ 'y < :

/ / r-;'y/ ,,/-, »< ,.--

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I IC1

f :..-CIC1 I Im_J

j II

+- - 1 Ic :Q

I IEQ) I-Q)

>1....

m

E. _~ -c, -1J

~

c:o

...

1

QJ:>-\\

co

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.-. . . . .uOJ

ecCuO Ja.'lo-

a.1

O J~

~

enVJC 1>'-a..

'-Q)

.cEm..co

Co,.,-

-

26

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2186-73-- --

4851903 0009830 0

.-D)

Cl-c o-

. . . . . .:J-

crQ)0:

C D

. .: : : : I. . . .CQa..IDa.E11.t: cm .-. . c a

.. ::I EII -. u ca.. . . . . .e, c• 0.s: NC II .-. - . ..c 0' t - . c :o )..., ac ....m Q3

E ,5ell =",-C+-

~ E~ . mI t;

r- -N

wc c:>o

e n

@

c: :

..

. . . . . .CJ

•Q. 1

C)

C J

m

. . . . . .'+-

..

-.-

-c ,~+-''-0

Ql

c:

s . . . (XOJ 3 a . .

. . . . . . .E 0

:::J /\(er

Q OJ

Q)

.--

a:

Q NN

> 0'- ecoE ~. . . . . . 0-e, -

".().

(xx/

(~ X)~ (xQ) y'> < 'x) y <- L..

Ql Q) ()<. c . c. . . ,

< X»:

= 0C O . c x <-5 u < ; < 0

en m >(L. Q) X

. . . I..-

I a

Q) QJ

o.cc.-C

t: .~,- .. .

Cl)-~

0.0

~-c

c nU

..r : : ~

'- c..-

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. . . . . . . . .u

0-c: Q)

Q)

tV .~

Cs . . .QJ

r. n 5 :c . . . . . .

~.I:

0 Q)

8 : 1 5 ,• 0E

1_ CZ Q)-

so~

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0+-' . . .Q) Q)

c.-C11_ s . . .Q. 0

0°

c: f. . . . .. . . , '-00(U

L.

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<(J E

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--

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-~- - ..

enL-a >.cE

Q) m::J ..cc- c.- c. E 0(J .~

O J co..... en

a J C

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GJ c:U) 0::J U

o Q). . . , - ' =UJ +a' _:

. - . . c : Q)

C......,111 Q)

.2 3 : -+- (0 Q)

~NEo III\ coC I) " " en

I..-m ~ Ql

> Cl s:.,p .- +J

co LL eE c 0(1) .._

.., c: -0- ::. Q)ct J > ......,

coc: .0 u« .t: 0

- e n -

I-

!Ec o.coc ::o. ,_..+-'(0enCOJ-cco(J

LL

27"

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ISO2186-1973 (E)---- --~~~ -- - - - - ---------.-.

4851903 0009831 2186-73

ANNEX A

FORMULAE FOR DIFFERENTIAL PRESSURE CALCULATION WHEN SEALING CHAMBERS ARE USED

NOTE - Figures 28 and 29 and corresponding calculation formulae (sections A.1 and A.2) relate to the case when the metered fluid is l ighter

than the sealing fluid.

A.1 MEASUREMENT BY MEANS OF A DIFFERENTIAL METER WITH A U-TUBE (Figure 28)

p -p =A B

p g

-

d 2A

---d 2B

HI

+ hA

I fP1A=P1S=P,

an d if P2A =P2B = = P 2

i.e. if th e m etered fluid ma ss d en sit y is the sam e in both higher and lower pressure branches

i.e. if the sealing fluid m ass density is the sam e in both sealing chambers,

then the formula giving the differential pressure m ay be simplified as follows:

•

I d 2\ B

dA2 d

A2

-- + ~DS2 DA 2

H '1 - H II+ hB A

H -H -hB A

d 2A

dA2 d

A2

+ ...·~----1dA2

H '-H '+h----B AL

-+1D 2A

d 2B

D 2B

If i.e. if both p re ssu re ta ps are at the same level,

i.e. if the reference planes (0 mark) ar e similar in both higher and lower p re ss ure b ra nc he s

respectively for sealing chambers on th e one hand an d meter on the other hand,

if H I = H I

A B

H"=H"A B

n d

then the formula giving th e differential pressure m ay be f urth er s im p lif ie d as follows:

28

d 2A

dA2 dA2

----+--Ds2 DA2

1+-d 2B

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--

I

-zw ... ..... .- ... . . . . . .

«P1A= t

m:t:

. . . .

-.

DA 08

2186-73 4851903 0009832 4

.. . . . . ;

' •

A B. . . . . . .-----. . . . . . . . . . :

--- - - - - - - --------

. .

-

..

'-

" aJ: : r :

.....

.r. p

..

FIG U R E 28 - D iffe rential meter with a U~tube

used with sealing chambers•

I ...

....

... ..

ISO-2186 ..1973 (E)

-... :

•

•

-

•..

29.

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ISO2186-1973 (E) -----~--- - -

2186-73 4851903 0009833 6

A.2 MEASUREMENT BY MEANS OF A 01FFERENTIAL METER WITH AN EQUALIZING VESSEL ON ONE BRANCH

(Figure 29)

- p g

- -_ _-

J

l.e, if th e m etered flu id m ass density is th e s ame in both h igher and lower pressu re branch esI fP1A==P1S=P,

and if P2A = = P2B =P2 i.e. if the sealing fluid mass density is the sam e in both sealing chambers ,

i.e. if b oth pressure taps ar e at the same level,

l.e, if th e reference planes (0 m ark) are similar in bo th higher and lower pressure branches

respectively fo r sealing cham bers on the one hand and meter on the other hand,

then the formula giving th e differential pressure m ay be si rnpl ified as follows:

dB

2

1 + a ~ ...

dA2

--+~b&-

=HB

=H'B

" "nd HA = HB

+ - -1

.. J

then the formula giving the d iffe re ntia l p re ss ure m ay be further simplified a s f o ll ow s :

30 ---- -

•-...

d 2B

2B

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..

«:r:

..

2186-73 4851903 0009834 8--

P1A c o

: r :1B

•

---------- - - - - - - --

4

P2B

P2A

-_....-. . . . . . . . .~--_.. _ - -.-... --... .-.-

p

FIGURE 29 - Differential meter with an equalizing vessel

on one branch, used with sealing chambers

r -- .. . - " - - :: w : : : - - . -- -: -1 1: 1. _ .- - _ _ __ .. . .. .. ..

-~

ISO 2186-1973 (E)

.

•

..

31:10.

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ISO 2186-1973 (E)

2186-73 4851903 0009835 0

ANNEX B

DESCRIPTION OF TYPICAL PROBE UNITS

General design requirements and installation details

Th e design of a suitable probe unit wi II depend on th e p artic u r ar tv pe of pr im ary el em ent used as we II as 0n th e flu id/sol idcharacteristics and it is an engineering design task that shou ld be left to ea ch in div id ual m a nu fa ctu re r.

However, it shou Id be noted that probes usually requ ire the use of pressu re holes larger than those norm ally chosen.

Nevertheless tap sizes beyond the upper Iimits given in ISO/R 541 shou Id not be u sed.

The length of th e probe itself should be such that when not in u se it can be fully withdrawn from th e mouth of the tap in th e

wall of the primary element. It is also necessary to ensu re that th e probe un i t valve, gland a nd p ip e arra ng em en ts shou ld not

allow any leakage that would cause spurious differential pressure signals.

As a guide to the design of a probe unit, Figure 30 shows a form of probe in comm on use. Figu re 31 shows a typical

installation that includes both probe units and settling chambers.

- - - ---- ---

32 -...•

-

~

-.. .. . . . . .

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2186-73 4851903 0009836 1ISO 2186-1973 (E)

I

Q.--0.Cco

: : : c

i

I

I

Q)

--0e-11

Q.

I

U)

Q)

.c0'-e,

c0..-.. . . .- -n

[

0c.e3 :

. . . .1

m

C

I-

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Gl

. . .~

.-3 :

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e,

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C

M

I-

f-

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c::>

= 'Q)

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mC

. . . . . . ...-c:::J

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Q_

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III\,'-~~-.

..

/ -- - -- - - - - -----------. p

- -~ -- "'-~ 33

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ISO 2186-1973 (E)2186-73 4851903 0009837 3

Centre-I ine of pri mary-element1

,ressure tap

---- ---- ---------- -- .---- ._--

""

-

-..

11

~---- Settl ing chamber/'

I

I

t

I·

-

~.-

)I

r'\

II1

Pipework connecting settling chambers

to pressure taps of primary elements

should be fitted on a gradient

approximately as shown.

•,I

I

t•

Centre-line of primary-element.__.....

pressure tap

r

·_- , .. . -----

•---~- -

1I --•,,,I

I,-

•

\

II•

Pressure tap boss----I

r

•II

·•

Probing spindle in fully

withdrawn position

..FIGURE 31 - Arrangement of probe unit

and settl ing chamber

r---~ -- -- . . . . . . . . . --- . . . . . . . . . . . . . . . . . . . . . . --

34 ...

.. ....•