Overview
ISO 451:1976 - "Aircraft - Pressure re-oiling connection" is an international standard that defines the mechanical interface for pressure re-oiling couplings used on aircraft engines. First published in June 1976 (with a figure erratum issued in 1980), the standard replaces the earlier ISO Recommendation R 451‑1965 and sets the basic dimensions, tolerances and the required clearance envelope for a re-oiling connection intended for use with all engine oils.
Key Topics and Requirements
- Scope: Specifies basic dimensions for pressure re-oiling connections and the space (clearance) envelope that must be provided on aircraft components.
- Dimensional data: Detailed dimensions and tolerances are provided in the standard’s figure and table (including diameters, lengths and envelope limits).
- Bayonet connection: The coupling uses three bayonet slots equally spaced at 120° ± 15', with a cutter diameter of 4.8 mm (0.1875 in) specified for the slot form.
- Valve positions: Illustrations define valve-open and valve-closed orientations and mating-face requirements (face must be at right angles to the axis of the coupling).
- Clearance envelope: A shaded clearance envelope is defined to ensure adequate space for coupling engagement and tool access during pressure re-oiling.
- Tolerances: Where not otherwise stated, dimensional tolerances are ±0.25 mm (0.01 in) and angular tolerances are ±0°30'.
- Erratum: A corrected figure was published in 1980; users should ensure they reference the updated drawing.
Practical Applications
- Ensures interchangeability of pressure re-oiling couplings across different aircraft engines and maintenance equipment.
- Guides the design of engine casings, access panels and lubrication fittings to accommodate a standard coupling and clearance envelope.
- Supports manufacturing of re-oiling adapters, hose fittings and bayonet couplings that must mate reliably under field maintenance conditions.
- Useful for maintenance procedures where pressurized oil is introduced into an engine system during servicing or troubleshooting.
Who Uses This Standard
- Aircraft and engine manufacturers designing lubrication interfaces
- Component and coupling manufacturers producing re-oiling fittings
- Aircraft maintenance, repair and overhaul (MRO) organizations
- Certification and quality engineers ensuring compatibility and compliance
- Suppliers and procurement teams specifying standard connectors for spares
Related Standards
- Work is linked to ISO Technical Committee ISO/TC 20 (aircraft). For full systems compliance, consult other ISO documents and manufacturer service bulletins addressing aircraft lubrication systems, pipe fittings and coupling interfaces.
Keywords: ISO 451, aircraft pressure re-oiling connection, pressure re-oiling coupling, aircraft lubrication systems, bayonet slots, coupling dimensions, clearance envelope.