SIST EN ISO 7278-2:1998
(Main)Liquid hydrocarbons - Dynamic measurement - Proving systems for volumetric meters - Part 2: Pipe provers (ISO 7278-2:1988)
Liquid hydrocarbons - Dynamic measurement - Proving systems for volumetric meters - Part 2: Pipe provers (ISO 7278-2:1988)
Provides guidance for the design, installation and calibration of these provers. Calculation techniques for use when calibrating and operating provers are detailed in ISO 4267-2. Most of the material is general in that it applies to provers for use with different liquids and types of meters and for proving them in different services. Does not apply to the newer "small volume" or "compact" provers.
Flüssige Kohlenwasserstoffe - Dynamische Messung - Prüfsysteme für volumetrische Meßgeräte - Teil 2: Rohrprüfer (ISO 7278-2:1988)
1.1 Dieser Teil von ISO 7278 behandelt Konstruktion, Installation und Kalibrierung von Rohrprüfern. Die Berechnungstechniken für das Kalibrieren und den Betrieb von Prüfern werden in ISO 4267-2 detailliert beschrieben. 1.2 Dieser Teil von ISO 7278 ist größtenteils allgemein gehalten im Hinblick auf Rohrprüfer, die bei unterschiedlichen Flüssigkeiten und Meßgerät-Typen benutzt und bei unterschiedlichen Betriebsabläufen geprüft werden können. Dieser Teil der Norm ISO 7278 bezieht sich nicht auf die neueren "Kleinvolumen" oder "Compact"Prüfer.
Hydrocarbures liquides - Mesurage dynamique - Systemes d'étalonnage des compteurs volumétriques - Partie 2: Tubes étalons (ISO 7278-2:1988)
1.1 La présente partie de l'ISO 7278 donne des indications concernant la conception, l'installation et l'étalonnage des tubes étalons. Les calculs techniques nécessaires pour l'étalonnage et l'utilisation des tubes étalons sont détaillés dans l'ISO 4267-2. 1.2 La plupart des sujets abordés dans la présente partie de l'ISO 7278 sont de nature générale : ils s'appliquent aux tubes étalons destinés à être utilisés pour différents liquides et avec différents types de compteurs pour permettre un étalonnage dans différentes conditions de service. Cette méthode ne s'applique pas aux «petits volumes» ou appareils de vérification «compact» de conception récente. 1.3 Les conditions de référence pour la mesure des produits pétroliers sont la température à 15 °C et la pression égale à 101 325 Pa, telles que mentionnées dans l'ISO 5024.
NOTE -- Dans certains pays, d'autres températures de référence sont utilisées (par exemple 20 °C et 60 °F).
Tekoči ogljikovodiki - Dinamična meritev - Sistemi za overjanje volumetrov - 2. del: Naprave za overjanje cevovodov (ISO 7278-2:1988)
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
SIST EN ISO 7278-2:1998
01-maj-1998
7HNRþLRJOMLNRYRGLNL'LQDPLþQDPHULWHY6LVWHPL]DRYHUMDQMHYROXPHWURYGHO
1DSUDYH]DRYHUMDQMHFHYRYRGRY ,62
Liquid hydrocarbons - Dynamic measurement - Proving systems for volumetric meters -
Part 2: Pipe provers (ISO 7278-2:1988)
Flüssige Kohlenwasserstoffe - Dynamische Messung - Prüfsysteme für volumetrische
Meßgeräte - Teil 2: Rohrprüfer (ISO 7278-2:1988)
Hydrocarbures liquides - Mesurage dynamique - Systemes d'étalonnage des compteurs
volumétriques - Partie 2: Tubes étalons (ISO 7278-2:1988)
Ta slovenski standard je istoveten z: EN ISO 7278-2:1995
ICS:
75.180.30 Oprema za merjenje Volumetric equipment and
prostornine in merjenje measurements
SIST EN ISO 7278-2:1998 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST EN ISO 7278-2:1998
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SIST EN ISO 7278-2:1998
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SIST EN ISO 7278-2:1998
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SIST EN ISO 7278-2:1998
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SIST EN ISO 7278-2:1998
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SIST EN ISO 7278-2:1998
ISO
INTERNATIONAL STANDARD
7278-2
First edition
1988-12-15
INTERNATIONAL ORGANIZATION FOR STANDARDIZATION
ORGANISATION INTERNATIONALE DE NORMALISATION
MEXJ/YHAPOJJHAFl OPTAHM3A~Mfl I-IO CTAH,4APTM3A~MM
Liquid hydrocarbons - Dynamit measurement -
Proving Systems for volumetric meters -
Part 2:
Pipe provers
S ystkmes d% talonnage des comp teurs
Hydrocarbures liquides - Mesurage dynamique -
volume triques
Partie 2: Tubes t+talons
Reference number
ISO 7278-2 : 1988 (E)
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SIST EN ISO 7278-2:1998
ISO 7278-2 : 1988 (El
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of
national Standards bodies (ISO member bodies). T.he work of preparing International
Standards is normally carried out through ISO technical committees. Esch 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, govern-
mental 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.
Draft International Standards adopted by the technical committees are circulated to
the member bodies for approval before their acceptance as International Standards by
the ISO Council. They are approved in accordance with ISO procedures requiring at
least 75 % approval by the member bodies voting.
International Standard ISO 7278-2 was prepared by Technical Committee ISO/TC 28,
Petroleum produc ts and lubrican ts.
Users should note that all International Standards undergo revision from time to time
and that any reference made herein to any other International Standard implies its
latest edition, unless otherwise stated.
0 International Organkation for Standardkation, 1988
Printed in Switzerland
ii
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SIST EN ISO 7278-2:1998
ISO 7278-2 : 1988 (EI
Page
Contents
1
.........................................................
0 Introduction
1
..........................................
1 Scope and field of application
1
2 References .
1
3 Definitions. .
2
................................................
4 Description of Systems
3
....................................
5 Essential Performance requirements.
3
6 Equipment .
5
7 Design of pipe provers .
7
8 Installation .
7
9 Calibration .
Annexes
............................. 15
A The use of pipe provers with four detectors
........ 18
Example of the calculation of the design Parameters of a pipe prover
B
Figures
12
..........................
1 Typical unidirectional return-type prover System
13
....................
2 Typical bidirectional straight-type Piston prover System
14
.........................
3 Typical bidirectional U-type sphere prover System
17
..............
4 Simultaneous use of two counters with a four-detector prover
17
...................
5 Temnorarv connection of counters to measure nl and n7
. . .
Ill
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SIST EN ISO 7278-2:1998
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SIST EN ISO 7278-2:1998
INTERNATIONAL STANDARD ISO 7278-2 : 1988 (E)
Dynamit measurement -
Liquid hydrocarbons -
Proving Systems for volumetric meters -
Part 2:
Pipe provers
1.2 Most of the material in this part of ISO 7278 is general in
0 IntroductioF
that it applies to pipe provers for use with different liquids and
types of meters and for proving them in different Services. This
Pipe provers are used as volume Standards for the calibration of
liquid meters. The purpose of this part of ISO 7278 is to outline part of ISO 7278 does not apply to the newer “small volume” or
“compact” provers.
the essential elements of a pipe prover, to provide speci-
fications for its Performance, and to give guidance on its
design, installation and calibration. Pipe provers discussed in
1.3 The Standard reference conditions for Petroleum
this part of ISO 7278 are of the running-start/running-stop
measurement are a temperature of 15 OC and a pressure of
type, in which flow is uninterrupted during proving, thus
101 325 Pa as specified in ISO 5024.
permitting the meter to be proved under its normal operating
conditions. This type of prover includes a calibrated section of
NOTE - In some countries other reference temperatures are used,
pipe in which a displacer travels, actuating detection devices e.g. 20 OC and 60 OF.
which produce electrical Signals as the displacer Passes each
end of the calibrated Portion. The displacer finally Stops at the
end of the run as it enters a region where the flow bypasses it.
2 References
ISO 2715, Liquid h ydrocarbons - Volumetric measurement b y
Both stationary and mobile provers may be constructed on this
turbine me ter s ys tems.
principle. The calibrated section of the prover may be straight
or folded (U-shaped), and the design may be such that the
ISO 4267-2, Petroleum and liquid Petroleum products -
displacer moves around a closed loop in only one direction
Calcula tion of oil quantities - Part 2: Dynamit
(unidirectional) or, alternatively, in both directions
measuremen t. 1)
(bidirectional) .
ISO 5024, Petroleum liquids and gases - Measuremen t -
ISO 7278 consists of the following Parts, under the general title
Standard reference conditions.
Liquid h ydrocarbons - D ynamic measuremen t - Pro ving
s ys tems for volume tric me ters :
ISO 7278-3, Liquid hydrocarbons - Dynamit measurement -
Proving s ystems for volumetric meters - Part 3: Pulse
- Part 7: General principles
in terpola tion techniques.
- Part 2: Pipe provers
ISO 8222, Petroleum measurement Systems - Calibration -
- Part 3: Pulse in terpolation techniques
Tempera ture corrections for use with volumetric reference
measuring s ystems.
Annex A forms an integral part of this part of ISO 7278.
Annex B is for information only.
3 Definitions
1 Scope and field of application For the purposes of this part of ISO 7278, the following
definitions apply:
1.1 This part of ISO 7278 provides guidance for the design,
Calculation 3.1 base volume: The volume of a prover calibrated
installation and calibration of pipe provers.
techniques for use when calibrating and sperating provers are section, i.e. the length between the detectors, at specified
detailed in ISO 4267-2. reference conditions of temperature and pressure.
1) At present at the Stage of draft.
1
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SIST EN ISO 7278-2:1998
ISO 7278-2 : 1988 (El
a) The manual-return unidirectional prover is an elemen-
3.2 K-factor: The ratio of the number of electrical pulses
tary form of in-line prover which uses a section of Pipeline
emitted by a meter during a proving run to the volume of liquid
as the prover section. The entire metered stream may flow
passed through the meter.
continuously through the prover even when the prover is
not being used for proving. Detectors are placed at selected
of the actual volu me of a liquid
3.3 meter factor: The ratio
Points which define the calibrated volume of the prover sec-
passed throu gh a meter to the volume indicated the meter.
bY
tion. A displacer launching device is upstream of the prover
section, and receiving facilities are installed at some Point
calibration : The procedure for determining the downstream of the prover section. Usually, conventional
34 prover
base volume of a prover. launching and receiving scraper traps are used for this pur-
pose. To make a proving run, a displacer (a sphere or
specially designed Piston) is launched, allowed to traverse
proof: The determination of the meter factor
3.5 proving;
the calibrated section, received downstream and then
or K-factor.
manually transported back to the launching site.
3.6 range: The differente between the highest and the
b) The automatic-return unidirectional (endless loop)
lowest values within a batch of results.
prover has evolved from the prover described in 4.2.1 a) and
is shown in figure 1. In this endless loop, the piping is
arranged so that the downstream end of the looped section
crosses over and above the upstream end of the loop. The
4 Description of Systems
interchange is the means whereby the displacer is transfer-
red from the downstream end to the upstream end of the
4.1 General
loop without removing it from the prover. The displacer
detectors are located at a suitable distance from the inter-
Change inside the looped Portion. Such endless prover
4.1.1 There are several types of pipe prover, all of which are
loops may be manually operated or they may be automated
relatively simple and commercially available. All types operate
so that the entire sequence for proving a meter tan be ac-
on a common principle, namely the precisely measured
tuated by a Single action. The metered stream may be per-
displacement of a volume of liquid in a calibrated section of
mitted to run through the prover when the prover is not
pipe between two signalling detectors, by means of a displacer
being used for proving, and the prover need not be isolated
(a slightly oversized sphere or Piston) being driven along the
from the carrier line unless desired. This permits the move-
pipe by the liquid stream being metered. While the displacer is
ment of several different types of liquid in succession
travelling between the two detectors, the output of the meter is
through the prover, and affords a self-flushing action which
recorded automatically. Pipe provers may be operated auto-
minimizes intermixing between them, as well as providing
matically or manually.
temperature stabilization.
4.1.2 A meter being proved on a continuous-flow basis shall,
at the time of proof, be connected to a counter which tan be
4.2.2 A meter proof run in a unidirectional prover consists of a
started or stopped instantly by the signalling detectors. The
Single one-way run, therefore the base volume of a unidirec-
counter is usually of the electronie-pulse-counting type. The
tional prover is the volume of liquid, corrected to Standard
counter is started and stopped by the displacing device ac-
temperature and pressure conditions, displaced between the
tuating the detector at each extremity of the calibrated section.
detectors during a Single trip sf the displacer.
4.1.3 There are two main types of pipe prover: unidirectional
and bidirectional. The unidirectional prover allows the displacer
to travel in only one direction through the proving section, and
4.3 Bidirectional provers
has a transfer arrangement for returning the displacer to its
starting Position. The bidirectional type allows the displacer to
The bidirectional prover has a Sength of pipe in which the
move first in one direction, then in the other. lt therefore incor-
displacer travels back and forth, actuating a detector at each
porates a means of reversing the flow through the pipe prover.
end of the calibrated section and stopping at the end of each
(See figures 1, 2 and 3.)
run when it emers a region where the flow tan bypass it or
when the action of a valve diverts the flow. Suitable sup-
plementary pipework and a reversing valve, or valve assembly,
4.1.4 Both unidirectional and bidirectional provers shall be
constructed so that the full flow through the meter being either manually or automatically operated, make possible the
reversal of the flow through the prover. The main body of the
proved Passes through the prover.
prover is often a straight piece of pipe (see figure 21, but it may
be contoured or folded (sec figure 3) so as to fit in a limited
4.2 Unidirectional provers
space or to make it more readily mobile. Normally, a sphere is
used as the displacer in the folded or contoured type and a
Piston is used in the straight-pipe type. A meter proof run
4.2.1 Unidirectional provers may be subdivided into two
usually consists of a “round trip” of the displacer, and the
categories depending on the manner in which the displacer is
displaced volume in this type of prover is expressed as the sum
handled, namely the manual-return in-line type sometimes
of the displaced volumes in two consecutive one-way trips in
referred to as a “measured distance” type, and the automatic-
opposite directions.
return or circulating type, often called the “endless loop” type.
2
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SIST EN ISO 7278-2:1998
ISO 7278-2 : 1988 (EI
and the design shall provide
5 Essential Performance requirements ab, for this requiremen t. All
weld ing shall be in accordance with applicable Codes.
shall ensure that the followi ng per-
The design of a pipe prover
formante requirements are met.
6.1.3 Internal coating of the prover section with a material
which will provide a hard, smooth, long-lasting finish will
reduce corrosion and wear and will prolong the life of the
5.1 Short-term repeatability
displacer and prover. Experience has shown that internal
coatings are particularly useful when the prover is used with
When a unidirectional prover is calibrated using the master
liquids having poor lubricating properties, such as gasoline or
meter method, the results of five successive calibration runs
LPG.
shall lie within a range of 0,02 %. When a bidirectional prover is
calibrated with a master meter, the results of five successive
runs each comprising a round trip of the displacer, shall be 6.2 Temperature stabilization
within a range of 0,02 %.
Temperature stabilization of the proving System is normally ac-
complished by the continuous circulation of liquid through the
The short-term calibration repeatability when using the
prover section, with or without insulation. When large portions
volumetric or gravimetric water draw methods shall be such
of the prover are buried and the liquids are at or near ground
that the results of three successive calibration runs are within a
temperature, additional insulation is usually not required. When
range of 0,02 %.
provers are installed above ground, the application of thermal
insulation will contribute to better temperature stabilization.
When a prover is used to prove a high-performance flow meter
Where a high temperature gradient tan appear along the prover
such as one suitable for custody transfer or fiscal measure-
Pipe, as with heated products, thermal insulation is recom-
ment, the results of five successive provings shall lie within a
mended.
range of 0,05 %.
63 . Temperature measurements
5.2 Valve seating
Temperatures shall be measured with an Overall uncertainty not
exceeding + 0,5 OC. This requires temperature Sensors with a
The sphere interchange in a unidirectional prover or the flow
certified accuracy of + 0,2 OC or better. The temperature
reversing valve or valves in a bidirectional prover shall be fully
Sensors shall be installed in thermowells near the inlet and
seated and sealed (so that the displacer is travelling at full
outlet of the prover and in positions which receive active fluid
velocity) before the displacer meets the first detector. These
flow during both normal and calibration operations. The
and any other valves whose leakage tan affect the accuracy of
thermowells shall be inserted to a minimum of 100 mm in large
proving shall be provided with some means of demonstrating
pipes and as closely as possible to one-half the diameter in
that they are sealed during the proving run.
small pipes. Thermowells shall be filled with a suitable heat
transfer medium. If mercury-in-glass thermometers are used,
5.3 Freedom from shock
they shall be of such a design that they tan be read while re-
maining immersed in the heat transfer medium to the recom-
When the prover is operating at its maximum design flow rate,
mended depth for the thermometer in use. lt is important to
the displacer shall come to rest safely and without shock at the
match the thermowell with a temperature Sensor of suitable im-
end of its travel. mersion requirements.
54 P Freedom from cavitation
64 . Pressure measurement
Pressure measurement devices shall be capable of measuring
When the prover is operating at its maximum design flow rate
pressure with an uncertainty of less than k 50 kPa ( + 0,5 bar)
and with the liquids for which it was designed, there shall be no
at pressures of up to 2 500 kPa (25 bar) and + 2 % of operating
risk of cavitation in the prover, valves or elsewhere, over the
pressure at higher pressures.
specified pressure and temperature range.
6.5 Displacing devices
6 Equipment
6.5.1 One type of displacing device commonly used in pipe
provers is the elastomer sphere filled with a liquid under
6.1 Materials and fabrication
pressure, and expanded so that its minimum diameter is slightly
larger than the inside diameter of the prover Pipe. The diameter
6.1.1 The materials selected for a prover shall conform with
shall be such that a seal is provided without excessive friction;
the applicable Codes specifying the pressure rating and the area
this tan usually be achieved by inflating the sphere to a
where the prover is to be used. Pipes, pipe fittings and bends
diameter which is at least 2 % greater than the inside diameter
shall be selected for internal roundness and smoothness.
of the prover Pipe. In general, the larger the sphere, the greater
this percentage should be. Too little expansion of the sphere
6.1.2 In the fabrication of provers, care shall be exercised to tan lead to leakage past the sphere and consequent measure-
ensure proper alignment and concentricity of pipe joints. All ment error. Too great an expansion of the sphere may not im-
welds within the path of the displacer shall be ground intern- prove sealing ability and will generally Cause the sphere to wear
3
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SIST EN ISO 7278-2:1998
ISO 7278-2 : 1988 (El
precision with which the detector in a prover tan detect the posi-
more rapidly and to move erratically. Care shall be exercised to
tion of the displacer (which is one of the governing factors in
ensure that no gas remains inside the sphere. The elastomer
determining the length of the prover section) shall be ascertained
shall be as impervious as possible to the operating liquids and
as accurately as possible (see annex AL The diameter of any
retain its mechanical properties (especially its elasticity) under
opening in the wall of the calibrated section of the Pipe, including
operating conditions. The liquid employed to fill the sphere
the holes accommodating the detectors, shall be appreciably less
shall have a freezing Point below any anticipated temperatures.
than the width of the sealing zone of the displacer.
Water or water-glycol mixtures are commonly employed.
6.9 Meter pulse generator
6.5.2 A second type of displacing device is the cylindrical
Piston with suitable Seals. This is often used with straight pipe
An externally fitted pulse generator shall generate electrical
provers that have been internally honed to ensure adequate
pulses of satisfactory characteristics for the type of proving
sealing.
counter employed. The device shall generate a sufficient
number of pulses per unit volume to provide the required
resolution. The pulse emitter shall be designed to eliminate the
6.5.3 Other displacers are acceptable if they give a perform-
ante equal to the two types mentioned in 6.5.1 and 6.5.2. generation of spurious pulses due to mechanical vibrations or
other influences.
6.6 Valves
6.10 Electronie pulse counter
An electronie pulse counter is usually used in meter proving
6.6.1 All valves used in pipe prover Systems which tan con-
because of the ease and accuracy with which it tan count high-
tribute to a bypass of liquid around the prover, the displacer or
frequency pulses and because of its ability to transmit its count
the meter, or which tan Cause leakage between prover and
to remote locations. The pulse-counting devices are equipped
meter, shall be bubble-tight on low differential pressure tests. A
with a Start-stop electronie switching circuit actuated by the
means of checking valve seal leakage during the proving run
prover’s detectors. Proving Systems tan also be equipped with
shall be provided for such valves. If a sphere or spheres are
a pulse interpolation System as defined in ISO 7278-3.
used to provide this sealing mechanism in lieu of a valve, they
shall be provided with some means of testing for leakage.
6.11 Equipment for automatic- retu
unidi rectional provers
6.6.2 The entire Operation of the flow reversing valve or
valves in a bidirectional prover, or of the interchange valve in a
6.11.1 Equipment necessary for the proper Operation of the
return type unidirectional prover, shall be completed before the
automatic-return or endless-loop unidirectional prover is cen-
displacer actuates the first detector. This is to ensure that dur-
tred around the sphere interchange unit. lt is within this unit
ing the trip of the displacer through the calibrated section no li-
that the sphere is diverted from the flowing stream at the
quid is allowed to bypass the prover. The necessary distance
downstream end of the prover, Passes through the interchange
between the initial Position of the displacer and the first detec-
and is then reinserted at the upstream end of the prover, all
tor, commonly called the pre-run, is dependent on valve opera-
automatically.
tion time and the velocity of the displacer. Any method tan be
used to shorten this pre-run, whether by faster Operation of the
valve or by delaying the launching of the displacer. However,
6.11.2 Sphere interchange may be accomplished with several
caution shall be exercised in the design so that hydraulic shock
different combinations of valves or other devices. Esch com-
or additional undesired pressure drop is not introduced. If more
bination comprises a System of devices designed to arrest the
than one flow directing valve is used, all valves shall be linked
sphere and pass it through the interchange, yet prevent any
by some means to ensure that shock cannot be caused by in-
flow of liquid through the interchange which would bypass the
correct sequence of Operation.
prover section during the proving period. Typical combinations
of devices are
6.7 Calibration connections
a) a Single special ball valve modified for sphere handling;
a dual power-operated check valve assembly;
b)
Connections shall be provided on the prover to allow for water
draw or master meter calibration at a later date (see figures 1,2
c) a combination of a ball or gate valve with a power-
and 3).
lrated check valve;
OPe
d) a dual through-conduit gate or ball valve;
6.8 Detectors
e) a valveless two- or three-sphere assembly;
f) an interchange using a plunger-type valve to block the
Detection devices and switches shall indicate the Position of
flow.
the displacer accurately, and in a bidirectional prover they shall
operate equally well in both directions. Various types of detec-
6.11.3 The controls and actuators used in connection with
tor are in use, the most common of which is the mechanically
actuated electrical switch. Other types, including the electronie unidirectional provers will depend primarily on the degree of
automation with which it is desired to operate the proving
proximity, the induction pickup or the ultrasonic type, may be
used, provided the required repeatability criteria are met. The System.
4
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SIST EN ISO 7278-2:1998
ISO 7278-2 : 1988 (EI
the degree of automation that will be incorporated
hl in
6.11.4 Separator tees, as shown in figure 1, are sized at least
the proving Operation;
one pipe size larger than the nominal size of the sphere or loop.
The design of the separator tee shall ensure dependable separa-
the size and type of meter that will be proved;
i)
tion of the sphere from the stream for all flow rates within the
j) the facilities that will be required for safely installing and
flow range of the prover.
removing the displacer;
facilities that
k) the will be required for safely venting and
6.11.5 Launching tees are generally one pipe size larger than
draining the prover.
the displacer sphere and shall have smooth transition fittings
leading into the prover. The launching tee shall have a slight in-
clination downwards toward the prover section, or some other
7.2 Diameter
means of ensuring movement of the sphere into the prover dur-
ing periods of low flow, such as might occur during calibration
In determining the diameters of the pipes to be used in the con-
by the water draw method.
necting lines, or manifolding, and the prover, the head loss
through the pipe prover System shall be compatible with the
head loss considered tolerable in the metering installation.
6.12 Equipment for bidirectional provers
Generally, the diameter of the pipe prover and manifolds shail
not be iess than the outlet diameter of any Single meter to be
6.12.1 In Piston-type bidirectional provers of the design
proved.
shown in figure 2, the outlets and inlets on the prover ends
shall be provided with holes or Slots. These shall be deburred
7.3 Volume
and shall have a total area greater than 1,5 times the cross-
sectional area of the pipe beyond the outlet. In sphere-type
bidirectional provers with oversized end chambers (see In determining the volume of a prover between detectors, the
figure 3), the chambers shail be designed so that the displacer following facto Irs shail be considered by the designer:
cannot obstruct the inlet or outiet openings and thus prevent
liquid from flowing. The receiving chambers shali be sized to
the Overall repeatability required of the proving System;
a)
ensure that the dispiacer is arrested without shock under
b) the repeatability of the detectors (see annex A,
maximum flow conditions.
clause A. 5);
the ability of the eiectronic counter to indicate oniy to
c)
6.12.2 A Single multiport valve is commonly used for revers-
the nearest pu lse, unless pulse interpolation is emp loyed;
ing the direction of liquid flow, and hence that of the displacer.
d) the discrimination of the meter Signal generator, that is,
Other means of fiow reversal may also be used. All valves shall
the volu me passing th rough the meter per pulse registered;
allow continuous flow through the meter during proving. The
valve size and actuator shail be selected to minimize pressure
the maximum permissibie fiow rate of the System.
4
drop and hydraulic shock.
7.4 Displacer velocity
7 Design of pipe provers
7.4.1 lt is not the intention of this part of ISO 7278 to limit the
velocity of displacers and, provided acceptable Performance is
7.1 Initial considerations
guaranteed, there shall be no arbitrary limit imposed upon
velocity.
Before considering the design of a pipe prover, it is necessary
to estabiish the type of prover required for the installation and
the manner in which it will be connected with the meter piping. 7.4.2 The maximum and minimum velocities of the displacer
From a study of the application, intended usage and space tan be determined from the diameter of the prover pipe and the
limitations, establish the following : maximum and minimum flow rates of the meters to be proved.
Clearly, some practical limit to maximum velocity of a displacer
must exist, partiy to avoid mechanical darnage to the prover,
a) whether the prover will be stationary or mobile;
partiy to limit surges and partly to prevent darnage to the
be dedicated (on-line) or
b) if stationary, whether it will
displacer and the detectors. Nevertheless, the developing state
used as part of a centrai System;
of the art is such that it is inadvisable to set a firm limit on
displacer velocity as a criterion of design. The minimum veioc-
c) if a stationary, dedicated pro
...
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