Liquid hydrocarbons — Volumetric measurement by displacement meter
ISO 2714:2017 describes and discusses the characteristics of displacement flowmeters. Attention is given to the factors to be considered in the application of positive displacement meters to liquid metering. These include the properties and nature of the liquid to be metered, the correct installation and operation of the meter, environmental effects, and the wide choice of secondary and ancillary equipment. Aspects of meter proving and maintenance are also discussed. ISO 2714:2017 is applicable to the metering of any appropriate liquid. Guidance is given on the use of positive displacement meters in the metering of two-component mixtures of the same phase such as water and oil. It is not applicable to two-phase flow when gases or solids are present under metering conditions (i.e. two-phase flow). It can be applied to the many and varied liquids encountered in industry for liquid metering only. It is not restricted to hydrocarbons. Guidance on the performance expected for fiscal/custody transfer applications for hydrocarbons is outlined. ISO 2714:2017 is not applicable to cryogenic liquids such as liquefied natural gas (LNG) and refrigerated petroleum gas. It does not cover potable water and fuel dispenser applications.
Hydrocarbures liquides — Mesurage volumétrique au moyen de compteurs à chambre mesureuse
Standards Content (Sample)
Liquid hydrocarbons — Volumetric
measurement by displacement meter
Hydrocarbures liquides — Mesurage volumétrique au moyen de
compteurs à chambre mesureuse
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© ISO 2017, Published in Switzerland
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1 Scope . 1
2 Normative references . 1
3 Terms, definitions, symbols and abbreviated terms . 1
3.1 Terms and definitions . 1
3.2 Symbols and abbreviated terms. 5
4 Design and operation of positive displacement meters . 5
4.1 Basic characteristics and mode of operation . 5
4.2 Reciprocating displacement types . 7
4.3 Rotating displacement types. 7
4.4 Intermeshing screw spindle type. 8
4.5 Oscillating displacement types . 9
4.6 Disc type meters . 9
5 Performance aspects . 9
5.1 General . 9
5.2 Factors affecting meter performance . 9
5.3 General performance characteristics . 9
5.4 Pressure drop and back pressure considerations .11
5.5 Flow profile .11
6 Liquid property effects .11
6.1 General .11
6.2 Effect of viscosity .11
6.3 Effect of temperature .13
6.4 Effect of pressure .13
6.5 Lubricity and liquid cleanliness .14
6.6 Two-phase flow and air elimination .14
6.7 Two-component operation .14
6.8 Pulsating and fluctuating flow .14
7 System design .15
7.1 Design considerations.15
7.2 Selection of displacement meter type .16
7.3 Ancillary equipment .17
7.3.2 Mechanical accessories .18
7.3.3 Pulse generators and secondary electronic instrumentation .18
7.4 Flow algorithms .19
8 Installation aspects .20
8.1 General .20
8.2 Installation pipework .20
8.3 Flow pulsation .22
8.4 Electrical installation .22
8.5 Pulse security .23
9 Environmental considerations .23
9.1 General .23
9.2 Electrical interference .23
9.3 Humidity .23
9.4 Safety .23
10 Calibration .24
10.1 Proving and verification .24
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10.2 General considerations .24
10.3 Proving conditions .24
10.4 Proving methods .24
10.5 Proving frequency .25
11 Operation and maintenance .25
11.1 General .25
11.2 Initial start-up .25
11.3 Meter maintenance .26
11.4 System diagnostics and control charts .26
Annex A (informative) Specification of performance.28
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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
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described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
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This document was prepared by Technical Committee ISO/TC 28, Petroleum and related products, fuels
and lubricants from natural or synthetic sources, Subcommittee SC 2, Measurement of petroleum and
related products, in collaboration with Technical Committee ISO/TC 30, Measurement of fluid flow in
This second edition cancels and replaces the first edition (ISO 2714:1980), which has been technically
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This document gives recommendations on the design, installation, operation and maintenance of
positive displacement meter systems used for liquid measurement. This widens the application scope
from the previous document, which was primarily aimed at hydrocarbon custody transfer applications.
The guidance now applies to all suitable liquids measured across different applications and industry
Displacement meters are extensively used in general fluid measurement in addition to fiscal, custody
transfer and legal metrology applications involving hydrocarbon and non-hydrocarbon products. These
can range from the light products such as gasoline, through to higher viscosity fluids.
The document has an extended scope from the first edition to cover applications for a wider range of
liquids and duties and to remove restriction to hydrocarbon liquids. It now provides guidance, rather
than mandatory requirements, on performance to allow meters to be specified and verified to meet
relevant regulatory, fiscal and custody transfer specifications. The document also now includes
additional meter designs. This revision has been achieved through the participation of ISO/TC 30 in the
preparation, hence, providing a single standard for the measurement of flowing liquids using positive
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INTERNATIONAL STANDARD ISO 2714:2017(E)
Liquid hydrocarbons — Volumetric measurement by
WARNING — The use of this document might involve hazardous materials, operations and
equipment. This document does not purport to address all of the safety problems associated
with its use. It is the responsibility of the user of this document to establish appropriate safety
and health practices.
This document describes and discusses the characteristics of displacement flowmeters. Attention
is given to the factors to be considered in the application of positive displacement meters to liquid
metering. These include the properties and nature of the liquid to be metered, the correct installation
and operation of the meter, environmental effects, and the wide choice of secondary and ancillary
equipment. Aspects of meter proving and maintenance are also discussed.
This document is applicable to the metering of any appropriate liquid. Guidance is given on the use of
positive displacement meters in the metering of two-component mixtures of the same phase such as
water and oil.
It is not applicable to two-phase flow when gases or solids are present under metering conditions (i.e.
two-phase flow). It can be applied to the many and varied liquids encountered in industry for liquid
metering only. It is not restricted to hydrocarbons.
Guidance on the performance expected for fiscal/custody transfer applications for hydrocarbons is
This document is not applicable to cryogenic liquids such as liquefied natural gas (LNG) and refrigerated
petroleum gas. It does not cover potable water and fuel dispenser applications.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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/IEC Guide 99, International vocabulary of basic and general terms in metrology (VIM)
ISO 4006, Measurement of fluid flow in closed conduits — Vocabulary and symbols
3 Terms, definitions, symbols and abbreviated terms
3.1 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https://www.iso.org/obp
— IEC Electropedia: available at https://www.electropedia.org/
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closeness of the agreement between the measured quantity value and a true quantity value of a
Note 1 to entry: The concept “measurement accuracy” is not a quantity, and should not be given a numerical value.
The quantitative expression of accuracy should be in terms of uncertainty. “Good accuracy” or “more accurate”
implies small measurement error. Any given numerical value should be taken as indicative of this.
[SOURCE: ISO/IEC Guide 99:2007, 2.13, modified]
set of operations carried out on a meter or measuring system so that it provides prescribed indications
corresponding to given values of the quantity measured
EXAMPLE This entails bringing a measuring instrument (meter) into a satisfactory performance and
Note 1 to entry: Adjustment can be of zero point, span, linearity or other factors affecting the performance of
Note 2 to entry: Adjustment should not be confused with calibration, which is a prerequisite for adjustment.
Note 3 to entry: After adjustment, a recalibration is usually required.
[SOURCE: ISO/IEC Guide 99:2007, 3.11]
set of operations that establish, under specified conditions, the relationship between quantities
indicated by an instrument and the corresponding values realized by standards
Note 1 to entry: Calibration should not be confused with adjustment of a measuring system.
[SOURCE: ISO/IEC Guide 99:2007, 2.39, modified]
phenomenon related to, and following, flashing (3.1.6), where vapour bubbles or voids form and
subsequently collapse or implode
Note 1 to entry: Cavitation causes significant measurement error and also potentially cause damage to the pipe
and meter through erosion.
measured value minus a reference value
Note 1 to entry: Relative error is error divided by a reference value. This can be expressed as a percentage.
[SOURCE: ISO/IEC Guide 99:2007, 2.16, modified]
phenomenon which occurs when the line pressure drops to, or below, the vapour pressure of the liquid,
allowing gas to appear from solution or through a component phase change
Note 1 to entry: Vapour pressure of the fluid can reduce with increasing temperature.
Note 2 to entry: Flashing is often due to a local pressure drop caused by an increase in liquid velocity, and
generally causes significant measurement error.
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Note 3 to entry: The free gas produced by flashing will remain for a considerable distance downstream of the
meter even if pressure recovers.
ratio of the number of pulses obtained from a meter and the quantity passed through the meter
total range of deviation of the accuracy curve from a constant value across a specified measurement range
Note 1 to entry: The maximum deviation is based on the mean of derived values at any one flow point.
Note 2 to entry: The deviation is the largest minus the smallest value of mean values at each flowrate.
Note 3 to entry: Relative linearity is the range of values divided by a specified value, e.g. the independent linearity
as defined in ISO 11631.
liquid property which affects friction between moving surfaces
Note 1 to entry: Good lubricity allows the formation of a liquid film between surfaces, and thereby reduces
friction. Poor lubricity, where little or no film is formed, can result in accelerated component wear.
ratio of the quantity indicated by the reference standard and the quantity indicated by the meter
derived value which may be used to indicate the performance of the meter
EXAMPLE Error, K-factor, or meter factor.
calibration (3.1.3) with comparison to defined acceptance criteria
Note 1 to entry: Proving is a term used in the oil industry and is similar to “verification”.
Note 2 to entry: Proving is a calibration, sometimes of limited measurement range, according to methods defined
by standards, regulation or procedures providing a determination of the errors of a meter and showing (proving)
it performs to defined acceptance criteria.
means of increasing the effective resolution of the pulses output from a meter by multiplying the pulse
frequency or measuring the fraction of a pulse associated with the total collected across a time period
Note 1 to entry: The latter is the most common method through a double timing technique.
set of values of flowrate for which the error (3.1.5) of a measuring instrument (flowmeter) is intended
to lie within specified limits
[SOURCE: ISO Guide 99:1993]
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range of values
difference between the maximum and minimum values of a set of values
Note 1 to entry: This can be expressed as a half range (±) number. Relative range is normally expressed as a
percentage of a specified value, e.g. mean, minimum or other calculated value.
closeness of agreement between indications or measured quantity values obtained by replicate
measurements under specified conditions
Note 1 to entry: Specified conditions normally imply the same reference, same conditions, same operators and
procedures and that the data are obtained sequentially over a short period of time.
Note 2 to entry: Repeatability can be expressed as the range (difference between the maximum and minimum)
values of error or K-factor. Alternatively, repeatability can be expressed as a function of the standard deviation
of the values.
Note 3 to entry: Dividing repeatability by the mean gives the relative value which can be expressed as a
percentage. Some standards suggest dividing by the minimum value.
[SOURCE: ISO/IEC Guide 99:2007, 2.21, modified]
measure of the fluid which passes through the meter without being directly measured
slip measured when the meter is rotating
slip measured when the meter is not rotating
conditions of temperature and pressure to which measurements of volume or density are referred to
standardize the quantity
Note 1 to entry: These are the specified values of the conditions to which the measured quantity is converted.
Note 2 to entry: For the petroleum industry, these are usually 15 °C, 20 °C or 60 °F and 101,325 kPa.
Note 3 to entry: Quantities expressed at standard conditions are shown by prefixing the volume unit by “S”, e.g.
4 Sm or 700 kg/Sm .
Note 4 to entry: Definition has been adapted from Energy Institute HM 0 and OIML R 117. Some other petroleum
standards employ the term “base” conditions.
Note 5 to entry: In some other documents, “standard” conditions are described as “base” conditions and,
incorrectly, as “reference” conditions. Reference conditions are conditions of use (influence quantities) prescribed
for testing the performance of a measuring instrument.
[SOURCE: ISO Guide 99:1993]
condition where the liquid flowing through a pipeline rotates with an associated high tangential
component of velocity relative to the axial component
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non-negative parameter characterizing the dispersion of the quantity values attributed to a measurand
based on the information used
[SOURCE: ISO/IEC Guide 99:2007, 2.26, modified]
Note 1 to entry: The uncertainty is normally expressed as a half width range along with the probability
distribution with that range. It can be expressed as a value or as a percentage of the perceived true value.
3.2 Symbols and abbreviated terms
For the purposes of this document, the symbols given in ISO 4006 and ISO/IEC Guide 99 apply.
NOTE The preferred unit for kinematic viscosity is metre squared per second (m /s) or millimetres squared
per second (mm /s). The practical unit used in this document is the industry recognized unit centistoke (cSt);
1 cSt = 1 mm /s.
4 Design and operation of positive displacement meters
4.1 Basic characteristics and mode of operation
Positive displacement (PD) flowmeters, as the name implies, are devices which continuously divide the
flowing stream into volumetric segments, and momentarily isolate these segments for measurement
purposes. The total of the volumes contained within the segments as the meter rotates over a period of
time is the total volume passed. The frequency at which the segments pass is a measure of the volume
flowrate. PD meters are driven by the flow, and it is the pressure drop across the meter internals that
creates a hydraulic imbalance which causes rotation.
All PD meters can be considered as possessing three basic elements: the external housing, the metering
element and the output shaft. The housing can be of single-case or double-case construction. The
external housing contains the fluid, and is designed to suit the operating conditions of temperature
and pressure. A double-case design minimizes the effect of pressure expansion on the outer external
housing by having a secondary internal housing around the metering element. The measuring unit is a
precise component (or series of components), which performs the liquid segmentation and comprises
a chamber and displacement mechanism. The cyclic volume displaced is a function of the number of
chambers or the precise design of the volume being swept by rotation or reciprocation.
The metering chamber (and the associated readout registers) is often sealed to prevent tampering and
fraud. Widespread type approval for trade use by relevant authorities is more common with PD meters
than most other types of flowmeter.
The output shaft is used to drive mechanical or electrical (pulsed) outputs. This could be a direct drive
to a pulse generator or through a gear box to a mechanical readout. Various calibration devices and
drives to compensators and printers can be attached. Some designs might have electronic pickups
fitted to detect rotation through the meter casing,