ISO 22181:2021

INTERNATIONAL ISO
STANDARD 22181
First edition
Aerospace fluid systems and
components — Variable displacement
hydraulic motors — General
specifications
PROOF/ÉPREUVE
Reference number
ISO 22181:2020(E)
©
ISO 2020

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ISO 22181:2020(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2020
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Published in Switzerland
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ISO 22181:2020(E)

Contents Page
Foreword .vi
Introduction .vii
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Classification . 7
5 General requirements . 7
5.1 Order of precedence . 7
5.2 Hydraulic system characteristics . 7
5.3 Airworthiness regulations . 8
5.4 Qualification . 8
6 Functional requirements . 8
6.1 Hydraulic fluid . 8
6.2 Pressures . 8
6.2.1 Rated supply pressure. 8
6.2.2 Rated differential pressure . 8
6.2.3 No-load break-out pressure . 8
6.2.4 Motor return port pressure . 9
6.2.5 Case drain pressure . 9
6.3 Flows . 9
6.3.1 Rated consumption . 9
6.3.2 Case drain flow . 9
6.3.3 Shaft seal leakage .10
6.3.4 External leakage .10
6.4 Speed and direction of rotation .10
6.4.1 Speed .10
6.5 Torque .11
6.5.1 Rated torque .11
6.5.2 Break-out torque .11
6.5.3 Stalling torque .11
6.5.4 Maximum stalling torque .11
6.5.5 Torque pulsations .11
6.6 Variable output load control .11
6.6.1 General.11
6.6.2 Response time .12
6.6.3 Stability .12
6.7 Motor overall efficiency .12
6.8 Dynamic characteristics .13
6.8.1 General.13
6.8.2 Dynamic braking .13
6.8.3 Rapid reversals .13
6.9 Passive operation .13
6.10 Fluid and ambient temperature .13
6.10.1 Fluid temperature .13
6.10.2 Ambient temperature .13
6.11 Acoustic noise level .14
6.12 Rated endurance .14
6.13 Environmental requirements .14
7 Detail design requirements .15
7.1 Dimensionally critical components .15
7.2 Maintainability features .15
7.3 Seals .15
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ISO 22181:2020(E)

7.4 Lubrication .15
7.5 Balance .15
7.6 Self-contained failure .16
7.7 Safety wire sealing .16
7.8 Electro-conductive bonding .16
7.9 Marking .16
7.9.1 Nameplate .16
7.9.2 Modification standard .16
7.9.3 Fluid identification .16
7.9.4 Ports .16
8 Strength requirements .17
8.1 General .17
8.2 Proof pressure .17
8.2.1 Motor case .17
8.2.2 Motor inlet port .17
8.2.3 Motor return port .17
8.3 Ultimate pressure .17
8.3.1 Motor case .17
8.3.2 Motor inlet port .17
8.3.3 Motor return port .17
8.4 Pressure impulse (fatigue) .17
8.5 Port strength .18
9 Construction requirements .18
9.1 Materials .18
9.1.1 General.18
9.1.2 Metals .18
9.2 Corrosion protection .18
9.2.1 General.18
9.2.2 Ferrous and copper alloys .19
9.2.3 Aluminium alloys .19
9.3 Castings .19
10 Installation requirements.19
10.1 Dimensions .19
10.2 Mass .19
10.3 Mounting .20
10.4 Orientation .20
10.5 Drive shaft .20
10.6 Ports .20
11 Maintenance requirements .21
11.1 Maintenance concept .21
11.2 Service life limitations and storage specifications .21
12 Reliability requirements .21
12.1 Equipment compliance .21
12.2 Requirements .21
13 Quality assurance provisions .21
13.1 Responsibility for inspection .21
13.2 Classification of tests .21
13.3 Test stand requirements .22
14 Acceptance tests .22
14.1 General .22
14.2 Examination of the product .22
14.3 Test programme .23
14.3.1 General.23
14.3.2 External leakage requirements .23
14.3.3 Break-in run .23
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ISO 22181:2020(E)

14.3.4 Proof pressure and overspeed tests .23
14.3.5 Operational tests at rated conditions .24
14.3.6 Break-out torque test .24
14.3.7 Teardown inspection examination .24
14.3.8 Run-in .25
14.3.9 Speed control test .25
14.3.10 Performance data .25
14.3.11 Fluid contamination test .26
14.4 Storage and packaging .27
15 Qualification procedures .27
15.1 General .27
15.2 Qualification procedure .27
15.2.1 Qualification by analogy .27
15.2.2 Motor qualification test report .27
15.2.3 Samples and program of qualification tests .27
15.3 Qualification testing .28
15.3.1 Dimensional check .28
15.3.2 Expanded envelope acceptance tests .28
15.3.3 Overspeed test .28
15.3.4 Operational test at overpressure .29
15.3.5 Calibration .29
15.3.6 Endurance testing .31
15.3.7 Environmental tests .34
15.3.8 Structural tests .35
15.3.9 Combination tests .37
15.3.10 Supplementary tests .37
Bibliography .38
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ISO 22181:2020(E)

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
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This document was prepared by Technical Committee ISO/TC 20, Aircraft and space vehicles,
Subcommittee SC 10, Aerospace fluid systems and components.
Any feedback or questions on this document should be directed to the user’s national standards body. A
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ISO 22181:2020(E)

Introduction
It is noted that, while ISO standards refer to SI units, large segments of the aerospace industry refer
to other measurement systems as a matter of common working practice. All dimensions used in this
document are in SI units with the non-SI units given in addition for the convenience of those users more
familiar with these.
It is further noted that the standard ISO decimal symbol “,” (comma) is not used as common working
practice for inch dimensions. A decimal point
...