ISO/DIS 11218.3

Aerospace -- Cleanliness classification for aeronautical fluids

Aéronautique et espace -- Classes de propreté des fluides aéronautiques

Standards Content (sample)

DRAFT INTERNATIONAL STANDARD ISO/DIS 11218.3
ISO/TC 20/SC 10 Secretariat: DIN
Voting begins on: Voting terminates on:
2010-08-12 2010-10-12

INTERNATIONAL ORGANIZATION FOR STANDARDIZATION • МЕЖДУНАРОДНАЯ ОРГАНИЗАЦИЯ ПО СТАНДАРТИЗАЦИИ • ORGANISATION INTERNATIONALE DE NORMALISATION

Aerospace — Cleanliness classification for aeronautical fluids
Aéronautique et espace — Classes de propreté des fluides aéronautiques
[Revision of first edition (ISO 11218:1993)]
ICS 49.080

In accordance with the provisions of Council Resolution 15/1993 this document is circulated in

the English language only.

Conformément aux dispositions de la Résolution du Conseil 15/1993, ce document est distribué

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ISO Central Secretariat work of editing and text composition will be undertaken at publication

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International Organization for Standardization, 2010
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ISO/DIS 11218.3
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ii ISO 2010 – All rights reserved
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ISO/DIS 11218.3
Contents Page

Foreword ............................................................................................................................................................iv

Introduction.........................................................................................................................................................v

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

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

3 Definitions..............................................................................................................................................2

3.1 particle size............................................................................................................................................2

3.2 particle size range.................................................................................................................................2

3.3 automatic particle counter (APC) ........................................................................................................2

3.4 cleanliness.............................................................................................................................................2

3.5 particulate contamination.....................................................................................................................2

4 Principle..................................................................................................................................................2

5 Sampling.................................................................................................................................................2

6 Particulate contamination analysis methods .....................................................................................2

6.1 Particle size analysis.............................................................................................................................2

6.2 Counting by microscopy ......................................................................................................................5

6.3 Counting by light extinction automatic particle counters.................................................................5

7 Determination of fluid particulate contamination level .....................................................................6

7.1 Equivalence with other standards .......................................................................................................6

7.2 Sizes and size ranges ...........................................................................................................................6

7.3 Particulate contamination levels.........................................................................................................6

8 Presentation and expression of results ..............................................................................................9

8.1 Particle counting results.......................................................................................................................9

8.2 Expression of results..........................................................................................................................10

8.2.1 Fluid contamination code...................................................................................................................10

8.2.2 Alphanumeric cleanliness code (optional) .......................................................................................10

8.2.3 Fluid contamination class ..................................................................................................................10

8.2.4 Examples..............................................................................................................................................10

Annex A (Informative ) Differences in particle size according to the APC used........................................12

A.1 Influence of APC calibration materials and method on particle apparent size.............................12

A.2 Influence of APC characteristics on apparent particle sizes..........................................................13

A.3 Impact on fluid contamination analysis results ...............................................................................14

Annex B (informative) Particle counting identification and reporting sheets ............................................15

Annex C (informative) Difference between NAS 1638 and ISO 11218 .........................................................17

Bibliography......................................................................................................................................................19

© ISO 2010 – All rights reserved iii
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ISO/DIS 11218.3
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies

(ISO member bodies). The work of preparing International Standards is normally carried out through ISO

technical committees. Each member body interested in a subject for which a technical committee has been

established has the right to be represented on that committee. International organizations, governmental and

non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the

International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.

International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.

The main task of technical committees is to prepare International Standards. Draft International Standards

adopted by the technical committees are circulated to the member bodies for voting. Publication as an

International Standard requires approval by at least 75 % of the member bodies casting a vote.

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

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

ISO 11218 was prepared by Technical Committee ISO/TC 20, Aircraft and Space Vehicles, Subcommittee

SC 10, Aerospace fluid systems and components.

This second edition cancels and replaces the first edition (ISO 11218:1993), which has been technically

revised. It significantly differs from the previous issue by the adoption of cumulative particle counting and

particle sizes in µm(c).
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ISO/DIS 11218.3
Introduction

The presence of particulate contamination in the fluid of aeronautical hydraulic systems has a deleterious

effect on both the components and the fluid making up hydraulic systems. To enhance performance, reliability

and safety, contamination has to be maintained at low levels. The appropriate level for a specific system will

depend upon the requirements of both the system and the operator, and will be specified.

There are many types of contamination (air, water, microorganismes, solid particles, chemicals, etc.). This

standard is concerned with contamination by solid particles. The level of contamination of aircraft hydraulic

fluids by solid particles shall be checked and maintained within a given definition range. The definition range is

characterised by the size and the number of particles. Determination of the size and numbers of particulate

contamination requires precision in obtaining the sample and in the analysis. If not errors will result and

erroneous conclusions will be drawn

Knowledge of contamination is essential to determine its origin and then to prevent it.

To simplify the reporting and analysis of data, ISO 11218 was developed to represent the particle count data

by a series of broadly based bands of contamination. The original version of ISO 11218 has been updated to

include technical improvements in measuring particles and also meet current and future requirements.

© ISO 2010 – All rights reserved v
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DRAFT INTERNATIONAL STANDARD ISO/DIS 11218.3
Aerospace — Cleanliness classification for aeronautical
fluids
1 Scope

This International Standard defines how to express the cleanliness of aeronautical fluids. The fluid

cleanliness is defined by comparing the measured contamination level to a specified cleanliness

threshold.

An aeronautical fluid is stated being clean when its measured contamination level is less than the

cleanliness / contamination level specified.
It details maximum allowable particle populations at defined sizes.

It uses the contamination classes specified in the previous 1993 version of this ISO and in the

NAS 1638 (superseded by AS4059) and NF L 41-101 standards.

The contamination classes expressed in compliance with the current standard cannot be compared to

those expressed in compliance with the ISO 4406 standard applicable to industrial hydraulic fluids.

2 Normative references

The following referenced documents are indispensable for the application of this document. For dated

references, only the edition cited applies. For undated references, the latest edition of the referenced

document (including any amendments) applies.

ISO 4407, Hydraulic fluid power — Fluid contamination — Determination of particulate contamination by

the counting method using an optical microscope.

ISO 11171, Hydraulic fluid power — Calibration of automatic particle counters for liquids.

ISO 11217, Aerospace — Hydraulic system fluid contamination — Location of sampling points and

criteria for sampling.

ISO 11500: Hydraulic fluid power — Determination of the particulate contamination level of a liquid

sample by automatic particle counting using the light-extinction principle

ISO TR 16386, Impact of changes in ISO fluid power particle counting, contamination control and filter

test standards.
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ISO/DIS 11218.3
3 Definitions

In this standard, the definitions given in ISO 4407 and ISO 11500 and the following definitions apply.

3.1 particle size

the longest dimension of the particle in case of microscopic counting or the diameter of the equivalent

sphere in case of automatic light extinction particle counting (see Figure 1)
3.2 particle size range
particle sizes included in a specified interval
3.3 automatic particle counter (APC)

instrument based on the light extinction principle able to size and record the passage of single particles

in the sample fluid and calibrated in accordance with ISO 11171. The measured particle size is equal to

the diameter of the sphere with the same projected area as the analysed particle.

3.4 cleanliness

condition of a fluid characterized by a level of particulate contamination lower than the specified level.

NOTE this term is preferred when one deals with a specification
3.5 particulate contamination
all undesirable particles which are in a fluid
NOTE this term is preferred when one deals with measurements
4 Principle

The cleanliness level of aerospace fluids is expressed by their particulate contamination levels. The

particulate contamination levels of fluids are measured by counting the number of particles in different

standard size ranges and referred to a volume of 100 mL of the fluid analysed. This contamination level

is expressed by a contamination code and/or a contamination class determined by comparing the

numbers measured to the acceptable numbers specified in Tables 1 and 2.
5 Sampling
Sampling shall be performed in accordance with ISO11217.
6 Particulate contamination analysis methods
6.1 Particle size analysis

Several methods and instruments based on different physical principles can be used to determine the

size distribution of the particles suspended in aeronautical fluids. The numbers of particles found in the

different size ranges characterize this distribution. A single particle may be sized differently depending

on both the size analysis technique and the method of calibration.
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ISO/DIS 11218.3
Figure 1 shows the particle being sized:

⎯ If the technique is the optical microscope then it will be sized by its longest dimension (1a) giving

13 μm (5). See Figure 1a.

⎯ If it is analysed using an APC calibrated in accordance with ISO 11171, it will be sized according to

its projected area (1b) equivalent diameter giving 10μm (7). See Figure 1b.
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ISO/DIS 11218.3
Key
1 Particle to be analyzed 4 Sphere with same longest dimension as actual
particle

1a Sized by microscope or image analysis based 5 Diameter of sphere with same longest

on “longest dimension” dimension (d = 13 µm)

1b Sized by APC calibrated as per ISO 11171 set 6 Spherical particle with same projected area as

up to give the “diameter of a sphere with the same actual particle (A = 78.5 µm )

equivalent projected area”

2 Particle longest dimension (d = 13µm) 7 Diameter of sphere with same projected area

as actual particle (d = 10µm(c) )
3 Particle projected area (A = 78.5 µm)
Figure 1 — Effect of the analysis technique on the reported size of a particle
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ISO/DIS 11218.3
6.2 Counting by microscopy

The operating procedure is described in ISO 4407, which covers the manual and image analysis

assisted microscopic counting methods. By convention, the size of particles is their longest dimension.

In case of dispute on analysis results using all other counting methods, the microscopic counting

method will be the reference method.
6.3 Counting by light extinction automatic particle counters

The operating procedure is described in ISO 11500. By convention, the size of the particle is the

diameter of the sphere with the same projected area. APCs are calibrated and validated in compliance

with the ISO 11171.

NOTE There are still companies using particle counters which may be calibrated in compliance with the ISO

4402 procedure (cancelled in 1999) based on non certified ACFTD powder. In case of dispute the customer may

require a particle counting with a device calibrated per ISO 11171. See ISO TR16386 for additional information. It is

recommended to have a correlation by cross check between APCs calibrated with ACFTD powder versus APC

calibrated with Standard Reference Material (SRM) 2806 prepared by the National Institute of Science and

Technology (NIST) in the USA, as illustrated in Annex A.

APCs are used either in clean atmospheres or in laboratory conditions with bottle samplers or fitted on-

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