EN 6138:2017

Aerospace series - Cap, protective, non-metallic for fitting ends ≤ 3 000 PSI hydraulic systems

This European Standard specifies the dimensions, tolerances and required characteristics of protective caps to seal fluid ports during transportation and storage in order to prevent:
-   contamination by moisture, fluids, chemicals and particles;
-   spillage inside package or aircraft section;
-   port and pipe end damages;
-   port and pipe clogging due to plug ingestion.
Because of the cleanliness requirements, parts shall only be used once.

Luft- und Raumfahrt - Kappe, nicht metallisch zum Schutz für Endfittinge ≤ 3 000 PSI Hydraulik Systeme

Diese Europäische Norm legt die Maße, Toleranzen und Kennwerte von Schutzkappen zum Abdichten von Fluidanschlüssen während des Transports und der Aufbewahrung fest, um Folgendes zu verhindern:
-   Verunreinigung durch Feuchtigkeit, Fluide, Chemikalien und Partikel;
-   Leckage innerhalb der Packung oder einer Luftfahrzeugsektion;
-   Beschädigung an Anschlüssen und Rohrenden;
-   Verstopfen von Anschlüssen und Rohren aufgrund des Ansaugens der Kappe.
Aufgrund der Reinheitsanforderungen dürfen die Teile nur einmal benutzt werden.

Série aérospatiale — Bouchon, de protection, non métallique pour raccord ≤ 3 000 PSI (21 000 kPa) circuits hydrauliques

La présente Norme européenne spécifie les dimensions, les tolérances et les caractéristiques requises pour les bouchons de protection destinés à l’étanchéité des orifices pour les liquides pendant le transport et le stockage afin d’éviter :
   une contamination par moisissure, fluides, produits chimiques et particules ;
   un renversement à l’intérieur de l’emballage ou de la section de l’aéronef ;
   des endommagements des orifices et de l'extrémité des tuyaux ;
   le bouchage des orifices et des tuyaux à cause de l'absorption de la fiche.
Dû aux exigences de propreté, les pièces ne doivent être utilisées qu’une seule fois.

Aeronavtika - Pokrov, zaščita, nekovinska, za končno vgradnjo ≤ 3 000 PSI hidravlični sistemi

Ta evropski standard določa mere, tolerance in zahtevane lastnosti zaščitnih pokrovov za zatesnitev odprtin za tekočino med prevozom in shranjevanjem, da se prepreči:
– kontaminacija z vlago, tekočinami, kemikalijami in delci;
– razlitje v embalaži ali predelu letala;
– nastanek poškodb na koncih odprtin in cevi;
– zamašitev odprtin in cevi zaradi vsrkanja vtiča.
Zaradi zahtev glede čistoče je treba dele uporabiti le enkrat.

General Information

• Status: Published
• Publication Date: 28-Mar-2017
• Withdrawal Date: 29-Sep-2017
• ICS: 49.080 - Aerospace fluid systems and components
• Technical Committee: ASD-STAN - Aerospace
• Drafting Committee: ASD-STAN/D 3 - Mechanical
• Current Stage: 6060 - Definitive text made available (DAV) - Publishing
• Start Date: 29-Mar-2017
• Completion Date: 29-Mar-2017
• Ref Project: SIST EN 6138:2017 - Aerospace series - Cap, protective, non-metallic for fitting ends ≤ 3 000 PSI hydraulic systems

Relations

• Refers: EN 9100:2018 - Quality Management Systems - Requirements for Aviation, Space and Defence Organizations
• Effective Date: 28-Jan-2026
• Refers: EN 12631:1999 - Fruit and vegetable juices - Enzymatic determination of D- and L-lactic acid (lactate) content - NAD spectrometric method
• Effective Date: 28-Jan-2026
• Refers: EN 2424:2008 - Aerospace series - Marking of aerospace products
• Effective Date: 28-Jan-2026
• Refers: EN 10244-1:2009 - Steel wire and wire products - Non-ferrous metallic coatings on steel wire - Part 1: General principles
• Effective Date: 28-Jan-2026

Overview

EN 6138:2017 is a European Standard developed by CEN that defines the specifications for non-metallic protective caps used in aerospace hydraulic systems with fitting ends rated up to 3,000 PSI. These caps are critical for sealing fluid ports during transportation and storage to maintain the safety and integrity of aerospace hydraulic systems. This standard details dimensions, tolerances, materials, marking, and packaging, ensuring consistent quality and preventing contamination and damage to hydraulic components.

Key aspects covered include contamination prevention, damage mitigation, and spillage control, emphasizing the one-time use requirement due to cleanliness standards.

Key Topics

• Dimensions and Tolerances
  EN 6138:2017 specifies exact dimensions, tolerances, and mass for protective caps, aligned with international ISO standards. The caps are designed to fit specific thread sizes and nominal tube diameters with precise measurements to ensure a tight seal.

• Material and Colour
  The caps are manufactured from high-density polyethylene (HD-PE), chosen for its resistance to phosphate ester hydraulic fluids per EN 6102. The standardized red color simplifies identification and aligns with aerospace color code standards (e.g., FED-STD-595C).

• Sealing and Pressure Resistance
  Caps must provide a consistent, reliable seal against port and pipe ends, preventing moisture and particle ingress. The standard mandates proof pressure validation at 100 kPa (1 bar) without leakage or deformation.

• Cleanliness and Usage
  Only one-time use is allowed due to stringent cleanliness requirements, conforming to SAE-AS4059 contamination class 7 or better, avoiding clogging or contamination of hydraulic systems.

• Marking and Packaging
  Each cap must be permanently marked with part designation and manufacturer information as per EN 2424. Packaging requirements ensure protection against moisture, contamination, and mechanical damage during transport and storage using chlorine-free materials.

• Quality Assurance
  Manufacturers need to operate under quality management systems compliant with EN 9100 or equivalent, ensuring consistent product quality and compliance with the standard.

Applications

• Aerospace Hydraulic Systems
  EN 6138:2017 caps are designed specifically for use in aerospace hydraulic fittings rated ≤ 3,000 PSI, protecting ports on aircraft hydraulic systems during assembly, storage, and transport.

• Transportation and Storage Protection
  These non-metallic protective caps prevent contamination by moisture, chemicals, and foreign particles, critical in maintaining system reliability and safety before installation.

• Maintenance and Handling
  During aircraft maintenance operations, protective caps are used to seal opened fluid ports to avoid spillage and damage, supporting system cleanliness and avoiding costly repairs or downtime.

• Component Preservation
  Preventing physical damage and clogging due to plug ingestion is vital during packaging and handling of aerospace hydraulic components, ensuring longer lifecycle and reduced failure risk.

Related Standards

• EN 6102 – Specifies technical requirements for phosphate ester-based fire-resistant hydraulic fluids compatible with these caps.
• EN 2424 – Defines the marking requirements for aerospace products, followed by EN 6138 for marking caps.
• EN 6079 – Details pipe coupling standards relevant for fitting ends these protective caps seal.
• ISO 2768-1 – Governs general linear and angular tolerances applied to the dimensions of caps.
• SAE-AS4059 – Classification of fluid contamination levels, ensuring the cleanliness criteria for caps are met.
• EN 9100 – Defines quality management requirements for aerospace organizations producing these caps.

Summary

EN 6138:2017 sets a critical benchmark for manufacturing, testing, and quality assurance of non-metallic protective caps for aerospace hydraulic fittings up to 3,000 PSI. The standard ensures the prevention of contamination, fluid spillage, and physical damage during transit or storage, thereby safeguarding the integrity of aerospace hydraulic systems. Compliance with this standard supports operational safety, component longevity, and industry-wide uniformity in aerospace fluid power protection solutions.

Standards Content (Sample)

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.V\VWHPV49.080Aerospace fluid systems and componentsICS:Ta slovenski standard je istoveten z:EN 6138:2017SIST EN 6138:2017en,fr,de01-junij-2017SIST EN 6138:2017SLOVENSKI
STANDARD
EUROPEAN STANDARD NORME EUROPÉENNE EUROPÄISCHE NORM
EN 6138
March
t r s y ICS
v {ä r z r English Version
Aerospace series æ Capá protectiveá nonæmetallic for fitting ends 
u
r r r PSI hydraulic systems Série aérospatiale æ Chapeauá protecteurá non métallique pour raccord 
u
r r r PSI circuits hydrauliques
Luftæ und Raumfahrt æ Kappeá nicht metallisch zum Schutz für Endfittinge 
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r r r PSI Hydraulik SystemeThis European Standard was approved by CEN on
t January
t r s yä
egulations which stipulate the conditions for giving this European Standard the status of a national standard without any alterationä Upætoædate lists and bibliographical references concerning such national standards may be obtained on application to the CENæCENELEC Management Centre or to any CEN memberä
translation under the responsibility of a CEN member into its own language and notified to the CENæCENELEC Management Centre has the same status as the official versionsä
CEN members are the national standards bodies of Austriaá Belgiumá Bulgariaá Croatiaá Cyprusá Czech Republicá Denmarká Estoniaá Finlandá Former Yugoslav Republic of Macedoniaá Franceá Germanyá Greeceá Hungaryá Icelandá Irelandá Italyá Latviaá Lithuaniaá Luxembourgá Maltaá Netherlandsá Norwayá Polandá Portugalá Romaniaá Serbiaá Slovakiaá Sloveniaá Spainá Swedená Switzerlandá Turkey and United Kingdomä
EUROPEAN COMMITTEE FOR STANDARDIZATION COMITÉ EUROPÉEN DE NORMALISATION EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre:
Avenue Marnix 17,
B-1000 Brussels
t r s y CEN All rights of exploitation in any form and by any means reserved worldwide for CEN national Membersä Refä Noä EN
x s u zã t r s y ESIST EN 6138:2017

EN 2424, Aerospace series — Marking of aerospace products EN 6079, Aerospace series — Pipe coupling
x z° cone — Female fitting endsá flareless type — Inch series1) EN 6102, Aerospace series — Fluid-hydraulicá phosphate ester-base, fire resistant — Technical specification1) EN 9100, Quality Management Systems — Requirements for Aviation, Space and Defence Organizations ISO 2768-1, General tolerances — Part 1: Tolerances for linear and angular dimensions without individual tolerance indications ISO 3161, Aerospace — UNJ threads — General requirements and limit dimensions SAE-AS4059, Aerospace Fluid Power — Contamination Classification for Hydraulic Fluids2) SA
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