ISO 14085-3:2015
(Main)Aerospace series — Hydraulic filter elements — Test methods — Part 3: Filtration efficiency and retention capacity
Aerospace series — Hydraulic filter elements — Test methods — Part 3: Filtration efficiency and retention capacity
ISO 14085-3:2015 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. ISO 14085-3:2015 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. ISO 14085-3:2015 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.
Série aérospatiale — Eléments filtrants hydrauliques — Méthode d'essais — Partie 3: Efficacité de filtration et capacité de rétention
General Information
Standards Content (Sample)
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 14085-3:2015(E)
©
ISO 2015
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ISO 14085-3:2015(E)
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ii © ISO 2015 – All rights reserved
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ISO 14085-3:2015(E)
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
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ISO 14085-3:2015(E)
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
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ISO 14085-3:2015(E)
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.
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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
calibration and validation
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ISO 14085-3:2015(E)
ISO 12103-1:1997, Road vehicles — Test dust for filter evaluation — Part 1: Arizona test dust
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 5598 and the following apply.
3.1
contaminant mass injected
mass of specific particulate contaminant injected into the test circuit to obtain the terminal
differential pressure
3.2
cyclic flow
change of flow from the specified rated flow rate to 25 % of rated flow rate at a specified frequency and
waveform
3.3
differential pressure
Δp
difference between the inlet and outlet pressures of the component under test, as measured under
specified conditions
Note 1 to entry: See Figure 1 and Figure 2 for graphical depiction of differential pressure (3.3) terms.
3.3.1
clean assembly differential pressure
difference between the tested component inlet and outlet pressure as measured with a clean filter
housing containing a clean filter element
3.3.2
clean element differential pressure
differential pressure (3.3) of the clean element calculated as the difference between the clean assembly
differential pressure (3.3.1) and the housing differential pressure (3.3.4)
3.3.3
final assembly differential pressure
assembly differential pressure at end of test equal to sum of housing plus terminal element differential
pressures (3.3.5)
3.3.4
housing differential pressure
differential pressure of the filter housing without an element
3.3.5
terminal element differential pressure
maximum differential pressure across the filter element as designated by the manufacturer or
specification to limit useful performance
3.4
filtration ratio
ratio of the number of particles larger than a specified size per unit volume in the influent fluid to the
number of particles larger than the same size per unit volume in the effluent fluid
Note 1 to entry: For steady flow testing, the filtration ratios (3.4) are designated with the Greek letter beta, ß.
Note 2 to entry: For cyclic flow (3.2) testing, the filtration ratios (3.4) are designated with the Greek letter sigma, σ.
3.5
free-flow dummy element
duplicate test filter element with its media layers removed to replicate the flow pattern in the housing
generated by the test filter element
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ISO 14085-3:2015(E)
3.6
rest conductivity
electrical conductivity at the initial instant of current measurement after a dc voltage is impressed
between electrodes
Note 1 to entry: It is the reciprocal of the resistance of uncharged fluid in the absence of ionic depletion or
polarization.
3.7
retention capacity
mass of specific particulate contaminant effectively retained by the filter element when terminal
element differential pressure is reached
Key
x test time or mass injected 3 clean element differential pressure
y differential pressure 4 housing differential pressure
1 final assembly (end of test) differential pressure 5 clean assembly differential pressure
2 terminal element differential pressure
Figure 1 — Differential pressure conventions for multi-pass test with steady flow
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ISO 14085-3:2015(E)
Key
3 clean element differential pressure at test flow rate
x test time or mass injected
(q )
f
Y differential pressure 4 housing differential pressure at test flow rate (q )
f
1 final assembly (end of test) differential pressure 5 clean assembly differential pressure at test flow rate
(q )
f
2 terminal element differential pressure at test flow
rate (q )
f
Figure 2 — Differential pressure conventions for multi-pass test with cyclic flow
4 Symbols and abbreviated terms
4.1 Graphic symbols used are in accordance with ISO 1219-1.
4.2 The letter symbols used in this part of ISO 14085 are shown in Table 1.
Table 1 — Letter symbols
Symbol Unit Description or explanation
particles/ml Overall average upstream count greater than size, x
A
u,x
particles/ml Overall average downstream count greater than size, x
A
d,x
mg/l Average base upstream gravimetric level
c
b
c ʹ mg/l Desired base upstream gravimetric level
b
mg/l Average injection gravimetric level
c
i
c ʹ mg/l Desired injection gravimetric level
i
c mg/l Test reservoir gravimetric level at 80 % assembly Δp
80
m G Mass of contaminant needed for injection
m G Estimated filter element capacity (mass injected)
e
m G Contaminant mass injected
i
m G Contaminant mass injected at element differential pressure
p
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ISO 14085-3:2015(E)
Table 1 (continued)
Symbol Unit Description or explanation
m G Retained capacity
R
n None Number of counts in specific time period
N particles/ml Number of upstream particles greater than size, x, at count, j
u,x,j
N particles/ml Number of downstream particles greater than size, x, at count, j
d,x,j
particles/ml Average upstream count greater than size, x, at time interval, t
N
u,x,t
particles/ml Average downstream count greater than size, x, at time interval, t
N
d,x,t
Δp Pa or kPa (bar) Differential pressure
Δp Pa or kPa (bar) Final assembly differential pressure
f
Δp Pa or kPa (bar) Net assembly differential pressure
n
Δp Pa or kPa (bar) Assembly differential pressure after increase of 2,5 % net Δp
2,5 %
Δp Pa or kPa (bar) Assembly differential pressure after increase of 80 % net Δp
80 %
l/min Average filter test flow rate
q
f
q l/min Discarded downstream sample flow rate
d
q l/min Filter rated flow (maximum flow for cyclic conditions)
f
q ʹ l/min Desired injection flow rate
i
l/min Average injection flow rate
q
i
q l/min Discarded upstream sample flow rate
u
t min Test time
tʹ min Predicted test time
t min Final test time
f
t min Test time at element differential pressure
p
t min Test time at beginning of 2,5 % stabilization period
2,5 %
t min Test time at beginning of 80 % stabilization period
80 %
V l Final measured injection system volume
if
V l Initial measured injection system volume
ii
V l Minimum required operating injection system volume
min
V l Final measured filter test system volume
tf
V l Minimum validated injection system volume
v
x, x1, x2 μm(c) Particle sizes
None Filtration ratio at particle size, x (steady flow)
β
x
None Filtration ratio at particle size, x, and time interval, t (steady flow)
β
x,t
None Average filtration ratio at particle size x, (steady flow)
β
x
σ None Filtration ratio at particle size, x, (cyclic flow)
x
σ None Filtration ratio at particle size, x, and time interval, t (cyclic flow)
x,t
None Average filtration ratio at particle size x, (cyclic flow)
σ
x
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ISO 14085-3:2015(E)
5 Test procedure overview
5.1 Set up and maintain apparatus in accordance with Clause 6 and Clause 7.
5.2 Validate equipment in accordance with Clause 8.
5.3 Run all tests in accordance with Clauses 9, 10, and 11.
5.4 Analyse and present data from Clause 11 in accordance with Clause 12.
6 Test equipment and supplies
6.1 Suitable timer
6.2 Sample bottles, use applicable sample bottles containing less than 100 particles greater than 6 μm(c)
per millilitre of bottle volume, as qualified per ISO 3722, to collect samples for gravimetric analyses.
6.3 Membrane filters and associated equipment, suitable for conducting gravimetric contamination
analysis in accordance with ISO 4405.
6.4 Test contaminant, use ISO Fine Test Dust (ISO FTD), grade A2 in accordance with ISO 12103-1,
dried at 110 °C to 150 °C for not less than 1 h for quantities less than 200 g.
Ensure that the ISO FTD used conforms to all the requirements of ISO 12103-1 grade A2, especially the
volume particle size distribution shown in ISO 12103-1:1997, Table 2
NOTE 1 This dust is commercially available. For availability of ISO Fine Test Dust, contact the ISO Central
Secretariat or member bodies of ISO.
NOTE 2 If the total quantity of ISO Fine Test Dust needed is greater than 200 g, batches not exceeding 200 g can
be prepared to make up the amount required.
NOTE 3 For use in the test system, it is recommended to mix the test dust into the test fluid, mechanically
2 2
agitate, then disperse ultrasonically in an ultrasonic bath that has a power density of 3 000 W/m to 10 000 W/m
provided it has been demonstrated that ultrasonic energy used does not affect the fluid viscosity.
6.5 Test fluid, petroleum base test fluid with properties as detailed in Annex A.
Another standard test fluid shall be used provided there is agreement between parties. Only filter test
results obtained with the same fluid shall be compared.
The temperature of the test fluid, during the test, shall be controlled at a value to result in a test fluid
2 2
kinematic viscosity of 15 mm /s ± 1 mm /s.
NOTE 1 The use of this hydraulic fluid ensures greater reproducibility of results and is based upon current
practices, other accepted filter standards, and its world-wide availability.
NOTE 2 The addition of an anti-static agent to this test fluid can affect the test results.
6.6 Particle counting systems
6.6.1 An online automatic particle counting system, per ISO 11943, shall be used to determine the
number and size distribution of the contaminant particles in the fluid. An online dilution system might
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ISO 14085-3:2015(E)
be required to ensure that the particulate concentration in the fluid sampled by the automatic particle
counters does not exceed the saturation limits specified by the automatic particle counter manufacturer.
The automatic particle counters, including the on-line dilution system, if applicable, should be validated
for on-line counting in accordance with ISO 11943.
6.6.2 A turbulent sampling means, in accordance with ISO 4021, shall be located upstream and
downstream of the test filter element in order to provide fluid sample flow to the automatic particle
counters. The design of the sampling system shall be such as to minimize lag time in fluid flow to the
automatic particle counters. The portion of the sampling flow not passing through the automatic particle
counters can be returned to the filter element test circuit reservoir via a by-pass line. Flow through the
automatic particle counters can also be returned to the filter element test circuit reservoir provided it has
not been diluted, or it can be discarded. Do not interrupt sample flow during the test.
6.6.3 Automatic particle counters shall be calibrated in accordance with ISO 11171 for the appropriate
particle sizes. Use the recommended particle sizes given in Table 3 unless otherwise agreed.
6.7 Test housing and free flow dummy element
6.7.1 The service filter housing shall be used whenever possible, and it shall be installed in a normal
service attitude. If this housing contains a by-pass valve, it shall be blocked and tested for zero leakage at
twice the normal cracking pressure.
6.7.2 If a service filter housing is not available, the test housing shall duplicate the inside configuration,
including size, direction, and location of the inlet and outlet flow ports used in the service filter housing.
The volume beyond the ends of the filter element can vary up to ±10 % of the corresponding volumes of
the actual housing.
6.7.3 Install a free flow dummy element in the filter housing when determining the differential pressure
of the empty filter assembly (i.e. without the filter element installed) to reduce the impact of any changes
in flow patterns on the measured filter element differential pressure. The free flow dummy element shall
be the same as the test element without the filter media. If the test filter element is not constructed with a
rigid core, the dummy element shall be provided with a core having a minimum open area equal to twice
the filter element outlet area (the internal cross-sectional area of the filter assembly outlet tube) and a
diameter approximating the inside diameter of the media pack.
6.8 Filter performance test circuits
The filter performance test requires two separate circuits: a filter element test circuit, and a contaminant
injection circuit. Schematic diagrams of typical filter performance test set-ups used to measure filtration
efficiency in steady and cyclic flow conditions are shown in Annex B.
6.8.1 Filter element test circuit, consisting of the following.
6.8.1.1 A reservoir with a smooth conical bottom that has an included angle of not more than 90°, pump,
fluid conditioning apparatus, and instrumentation that are capable of accommodating the range of flow
rates, pressures, temperatures, and volumes required by the procedure, and is capable of meeting the
validation requirements of Clause 8.
6.8.1.2 A clean-up filter capable of providing an initial system contamination level as specified in Table 3.
6.8.1.3 A configuration that is insensitive to the intended operative contaminant level.
6.8.1.4 A configuration that does not alter the test contaminant distribution over the anticipated test duration.
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ISO 14085-3:2015(E)
6.8.1.5 Pressure taps in accordance with ISO 3968.
6.8.1.6 Fluid sampling sections upstream and downstream of the test filter in accordance with ISO 4021.
6.8.1.7 Fluids entering the reservoir shall be diffused. Diffusion should take place below the reservoir
fluid surface in order to eliminate the formation of air bubbles.
6.8.1.8 For cyclic flow testing, a cyclic flow by-pass line equipped with an automatically controlled
shut-off valve (e.g. an electrically-actuated ball valve or poppet type valve, which has been shown to be
satisfactory for this application) or other method capable of producing the required flow rate cycle at the
test frequency shall be used.
The flow cycling set-up shall be capable of cycling at 0,1 Hz. Each 10 s cycle shall consist of two equal
parts, the first including a flow rise period (25 % to 100 % of the test flow rate, q ) and a constant 100 %
f
flow period, followed by the second part including a flow decay back to 25 % q and a constant 25 % flow
f
period. This is accomplished via the solenoid operated shut-off valve and the flow control valve in the
by-pass circuit shown in Figure B.2 or using an alternate acceptable method. The set-up should be such
that the flow cycle falls within the limits set forth in Figure 3.
key
x time after start of flow cycle 2 25 % of filter rated flow, 0,25 q
f
y differential pressure 3 rise time = 0,1 s to 0,2 s
1 filter rated flow, q 4 fall time = 0,1 s to 0,2 s
f
Figure 3 — Flow cycle waveform
Alternatively, any other specified frequency or cycle waveform (minimum or maximum flow, and rise and
...
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