ISO 3323:2023

Aircraft - Hydraulic components - Marking to indicate the fluid for which a component is approved

This document establishes a scheme for the marking of components (other than pipelines, hoses and fittings) used in aircraft hydraulic systems, so that the correct type of fluid is readily apparent during any assembly or testing operations in workshops. The marking is not intended to serve any purpose when a component is installed in an aircraft.

Aéronefs — Composants hydrauliques — Marquage indiquant le fluide pour lequel les composants sont approuvés

General Information

• Status: Published
• Publication Date: 15-May-2023
• ICS: 49.080 - Aerospace fluid systems and components
• Technical Committee: ISO/TC 20/SC 10 - Aerospace fluid systems and components
• Drafting Committee: ISO/TC 20/SC 10 - Aerospace fluid systems and components
• Current Stage: 6060 - International Standard published
• Start Date: 16-May-2023
• Due Date: 16-Sep-2023
• Completion Date: 16-May-2023

Relations

• Revises: ISO 3323:1987 - Aircraft - Hydraulic components - Marking to indicate fluid for which component is approved
• Effective Date: 06-Jun-2022

Overview

ISO 3323:2023 defines a marking scheme for aircraft hydraulic components (excluding pipelines, hoses and fittings) to indicate the specific hydraulic fluid for which each component is approved. The purpose is to make the correct fluid readily apparent during assembly, testing and workshop operations. The marking is intended for handling and maintenance stages - it is not required to serve any function when the component is installed in-service.

Key topics and requirements

• Scope of marking: Applies to components used in aircraft hydraulic systems except pipelines, hoses and fittings (those are covered by ISO 12).
• Fluid categories: Marking must state one of the defined fluid types:
  • Mineral oil base
  • Synthetic hydrocarbon base
  • Chlorinated silicone base
  • Phosphate ester base
  • Castor base
  • Silicate ester base
• Plate / label design:
  • Components shall carry a plate or label clearly marked with the fluid name; optional inclusion of a product name or specification number is permitted (e.g., ISO 9940, AS1241, MIL-PRF-5606).
  • Plates (or labels) must be neutral in colour except for phosphate ester based fluids, which require a violet label specified by CIE chromaticity x = 0.337, y = 0.242 and spectral radiance factor β = 6.5% (CIE standard illuminant B).
• Materials & attachment:
  • Plates shall be durable and resistant to hydraulic fluids and environmental conditions (examples: anodized metal, suitable plastics).
  • Plates must be securely and visibly fixed; for fluids likely to corrode glued joints (e.g., phosphate ester) mechanical attachment is required.
• Sizing & legibility:
  • Preferred plate dimensions are indicated (examples: 15 × 5 mm, 30 × 10 mm, 50 × 17 mm) with corner radii; lettering should be as large as practicable relative to plate size.

Applications and users

ISO 3323:2023 is primarily used by:

• Aircraft component manufacturers (OEMs) specifying identification plates on hydraulic components
• Maintenance, repair and overhaul (MRO) workshops and assembly technicians
• Procurement and quality assurance teams ensuring fluid compatibility and traceability
• Suppliers and parts distributors preparing components for workshop handling

Practical benefits include reduced risk of fluid contamination, clearer maintenance procedures, improved safety during assembly/testing, and easier compliance with procurement and maintenance specifications.

Related standards

• ISO 12 - Aerospace - Pipelines - Identification
• ISO 9940 - Phosphate ester-base hydraulic fluid (technical specification)
• MIL-PRF-5606, MIL-PRF-83282, MIL-PRF-87257 (military hydraulic fluid specs)
• SAE AS1241, NSA307110, BMS 3-11

Keywords: ISO 3323, aircraft hydraulic components, fluid identification, identification plate, phosphate ester, hydraulic fluid marking, aerospace maintenance.

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 3323
Third edition
2023-05
Aircraft — Hydraulic components —
Marking to indicate the fluid for which
a component is approved
Aéronefs — Composants hydrauliques — Marquage indiquant le
fluide pour lequel les composants sont approuvés
Reference number
© ISO 2023
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
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ISO copyright office
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Published in Switzerland
ii
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Scheme . 1
5 Materials, design and manufacture .1
Bibliography . 4
iii
Foreword
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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.
This third edition cancels and replaces the second edition (ISO 3323:1987), which has been technically
revised.
The main changes are as follows:
— Figure 1 (phosphate ester based fluid) was updated;
— Figure 2 (hydraulic fluid) was added.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv
INTERNATIONAL STANDARD ISO 3323:2023(E)
Aircraft — Hydraulic components — Marking to indicate
the fluid for which a component is approved
1 Scope
This document establishes a scheme for the mark
...