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NAS1611-204 – Aerospace Preformed O-Ring
Part Number: NAS1611-204
Manufacturer: National Aerospace Standard (AIA/NAS)
Military Specification: NAS1611 (Dash size -204)
Material Class: Ethylene Propylene (EPDM)
Overview Section
The NAS1611-204 is a high-performance aerospace-grade O-ring designed for static and dynamic sealing in aircraft systems. It is part of the NAS1611 series, which is specifically engineered for compatibility with Phosphate Ester hydraulic fluids (such as Skydrol).
The "-204" dash size refers to its specific dimensional profile, following the standard aerospace sizing convention (equivalent to AS568-204). Because of its Ethylene Propylene composition, this O-ring is essential for hydraulic systems, environmental control units, and brake assemblies where petroleum-based seals would rapidly degrade and fail.
Enhanced Technical Data
| Technical Metric | Specification Data |
| Inside Diameter (ID) | 0.359 in (9.12 mm) |
| Cross-Section (W) | 0.139 in (3.53 mm) |
| Outside Diameter (OD) | 0.637 in (16.18 mm) |
| Material Base | Ethylene Propylene (EPDM / NAS1613 Class 1) |
| Durometer (Hardness) | 80 Shore A (Nominal) |
| Operating Temperature | $-65°F$ to $+250°F$ ($-54°C$ to $+121°C$) |
| Fluid Compatibility | Phosphate Ester (Skydrol), Water, Steam, Dilute Acids |
| Dash Size Series | 200 Series (Standard 1/8" Cross-Section) |
Advanced Engineering & Structural Application
The NAS1611-204 is engineered for Skydrol Resistance and High Compression Set Resistance. In modern commercial and business jet hydraulic systems, the use of phosphate ester fluids requires specific elastomeric compounds that will not swell or become brittle.
Engineering Insight: The NAS1613 Compound Requirement
The NAS1611 series O-rings are typically manufactured to meet the NAS1613 material specification. This standard ensures that the elastomer maintains its tensile strength and "memory" (elastic recovery) even after prolonged exposure to hydraulic pressure and thermal cycling. The 80 Shore A hardness provides a balanced "squeeze," allowing the seal to handle pressures up to 1,500 PSI without a backup ring, and higher pressures when reinforced.
Dimensional Precision
Unlike standard industrial O-rings (AS568), the NAS1611 series often adheres to tighter Class 1 tolerances. This is critical for aerospace "glands" (the grooves the O-ring sits in) where precise "volume-fill" is necessary to prevent seal "nibbling" or extrusion under high-pressure pulses.
Aircraft Compatibility
The NAS1611-204 is a staple in the Illustrated Parts Catalogs (IPC) of major airframes:
Textron Aviation: Found in Cessna Citation (V, Ultra, Encore) hydraulic and environmental systems.
Bombardier: Extensively used in Challenger and Global series landing gear and brake modules.
Boeing / Airbus: Secondary structural and flight control actuator seals.
General Aviation: Utilized in high-performance turboprops using Skydrol-based hydraulic circuits.
The NAS1611-204 is the definitive sealing solution for aircraft systems utilizing phosphate ester hydraulic fluids. Engineering safety into a pressurized airframe requires hardware that can withstand the aggressive chemical nature of Skydrol while maintaining a hermetic seal at sub-zero temperatures. With its high-durometer EPDM compound and precision aerospace dimensions, the NAS1611-204 provides the chemical stability and mechanical toughness required for long-interval service life. Trust genuine NAS-standard O-rings to protect your hydraulic actuators and brake assemblies from leaks and contamination.
Installation & Maintenance Addendum
Chemical Warning: NEVER use the NAS1611-204 in systems containing petroleum-based oils or fuels (MIL-H-5606). Petroleum will cause EPDM seals to swell to several times their size, leading to total system failure.
Lubrication: Only lubricate with an approved phosphate ester-based grease or the system fluid itself during installation to prevent "rolling" or "spiraling" the O-ring in the gland.
Visual Inspection: NAS1611 series O-rings are typically Black but may have a specific color stripe (often purple or blue) depending on the manufacturer to denote phosphate ester compatibility. Always verify the part number on the sealed packaging.
