ISO 14085-3:2015

INTERNATIONAL ISO
STANDARD 14085-3
First edition
2015-03-01
Aerospace series — Hydraulic filter
elements — Test methods —
Part 3:
Filtration efficiency and retention
capacity
Série aérospatiale — Eléments filtrants hydrauliques — Méthode
d’essais —
Partie 3: Efficacité de filtration et capacité de rétention
Reference number
©
ISO 2015
© ISO 2015
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ii © ISO 2015 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Symbols and abbreviated terms . 4
5 Test procedure overview . 6
6 Test equipment and supplies. 6
7 Instrument accuracy and allowable test condition variation .10
8 Test equipment validation .10
9 Summary of information required prior to testing .14
10 Preliminary test preparation .14
10.1 Test filter assembly .14
10.2 Contaminant injection system .14
10.3 Steady flow filter test system .15
10.4 Cyclic flow filter test system .17
11 Filter element efficiency test .17
11.1 Steady flow test.17
11.2 Cyclic flow test .18
12 Calculation and data reporting .20
12.1 Filtration ratio and retention capacity .20
12.2 Calculation of stabilized particle counts for cyclic flow test .24
13 Identification statement (reference to this part of ISO 14085) .25
Annex A (normative) Properties of test fluid to evaluate performance of hydraulic fluid
systems filter elements .30
Annex B (informative) Test system design guide .32
Bibliography .37
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.
The procedures used to develop this document and those intended for its further maintenance are
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
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
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. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the meaning of ISO specific terms and expressions related to conformity
assessment, as well as information about ISO’s adherence to the WTO principles in the Technical Barriers
to Trade (TBT) see the following URL: Foreword - Supplementary information
The committee responsible for this document is ISO/TC 20, Aircraft and space vehicles, Subcommittee
SC 10, Aerospace fluid systems and components.
ISO 14085 consists of the following parts, under the general title Aerospace series — Hydraulic filter
elements — Test methods:
— Part 1: Test sequence
— Part 2: Conditioning
— Part 3: Filtration efficiency and retention capacity
— Part 4: Verification of collapse/burst pressure rating
— Part 5: Resistance to flow fatigue
— Part 6: Initial cleanliness level
iv © ISO 2015 – All rights reserved

Introduction
In aerospace hydraulic fluid power systems, power is transmitted and controlled through a liquid
under pressure. The liquid is both a lubricant and power-transmitting medium. The presence of solid
contaminant particles in the liquid interferes with the ability of the hydraulic fluid to lubricate, and
causes wear and malfunction of the components. The extent of contamination in the fluid has a direct
bearing on the performance, reliability, and safety of the system, and needs to be controlled to levels
that are considered appropriate for the system concerned.
Different principles are used to control the contamination level of the fluid by removing solid contaminant
particles; one of them uses a filter element enclosed in a filter housing. The filter element is the porous
device that performs the actual process of filtration. The complete assembly is designated as a filter.
The performance characteristics of a filter are a function of the element (its medium and geometry) and
the housing (its general configuration and seal design). For a given filter, the actual performance is a
function of the characteristics of the liquid (viscosity, temperature, conductivity, etc.), the particles in
suspension (size, shape, hardness, etc.), and the flow conditions.
A standard multi-pass method for evaluating the performance of hydraulic fluid filter elements under
steady state conditions has been developed and used for several years, and is referred to in several
aircraft hydraulic systems specifications.
Most aircraft hydraulic systems are subjected to unsteady flow with flow cycles caused by such conditions
as actuator movement. Such flow variations can have a significant impact on filter performance. To
enable the relative performance of hydraulic filters to be reliably compared so that the most appropriate
filter can be selected, it is necessary to perform testing with the same standard operating conditions.
This part of ISO 14085 describes two test methods and the equipment required to measure hydraulic
filter element performance with multi-pass flow in both steady and cyclic conditions.
The influence of other stressful operating conditions, such as heat, cold, and vibration, are not measured
with this procedure alone. The influence of such conditions is determined with pre-conditioning being
performed on the test filter element prior to efficiency testing (refer to ISO 14085-1 for descriptions of
such tests and when they are applied).
The stabilized contamination level measured while testing with cyclic flow gives an indication of the
average contamination level maintained by the filter in a dynamic operating system. The average system
contamination level is important in establishing wear rates and reliability levels.
The measurements are made with precise control over the operating conditions in particular the test fluid
and test contaminant, to ensure repeatability and reproducibility. However, because the test parameters
and test contaminant do not exactly replicate actual operating conditions which significantly differ
from one system to another, the measurements cannot be expected to duplicate actual performance in
an operating system.
INTERNATIONAL STANDARD ISO 14085-3:2015(E)
Aerospace series — Hydraulic filter elements — Test
methods —
Part 3:
Filtration efficiency and retention capacity
1 Scope
This part of ISO 14085 describes two methods to measure in repeatable conditions the filtration
efficiency of filter elements used in aviation and aerospace hydraulic fluid systems. It can be applied
when evaluating the overall characteristics of a filter element per ISO 14085-1, or separately.
Since the filtration efficiency of a filter element can change during its service life as it is clogging, this
test method specifies its continuous measurement by using on-line particle counters with continuous
injection of test contaminant and recirculation of particles not retained by the test filter element until
the differential pressure across the element reaches a given final or “terminal” value.
This part of ISO 14085 allows the efficiency to be measured under both steady or cyclic flow conditions.
It also is applied to measure the stabilized contamination levels that are produced by the filter element
while testing with cyclic flow.
This part of ISO 14085 is not intended to qualify a filter element under replicate conditions of service;
this can only be done by a specific test protocol developed for the purpose, including actual conditions
of use, for example the operating fluid or contamination.
The tests data resulting from application of this part of ISO 14085 can be used to compare the performance
of aerospace hydraulic filter elements.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
ISO 1219-1, Fluid power systems and components — Graphical symbols and circuit diagrams — Part 1:
Graphical symbols for conventional use and data-processing applications
ISO 2942, Hydraulic fluid power — Filter elements — Verification of fabrication integrity and determination
of the first bubble point
ISO 3968, Hydraulic fluid power — Filters — Evaluation of differential pressure versus flow characteristics
ISO 4021, Hydraulic fluid power — Particulate contamination analysis — Extraction of fluid samples from
lines of an operating system
ISO 4405, Hydraulic fluid power — Fluid contamination — Determination of particulate contamination by
the gravimetric method
ISO 5598, Fluid power systems and components — Vocabulary
ISO 11171, Hydraulic fluid power — Calibration of automatic particle counters for liquids
ISO 11943, Hydraulic fluid power — On-line automatic particle-counting systems for liquids — Methods of
calibratio
...