AS3209-018 - Packing Preformed Fluorocarbon O-Ring

AS3209-018 – Fluorocarbon (Viton®) Boss Seal O-Ring, 75 Durometer

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Overview

The AS3209-018 is a high-performance, preformed O-ring packing seal manufactured to the precise Aerospace Standard (AS3209). This O-ring is fabricated from a Fluorocarbon (FKM) elastomer, a material widely known by its DuPont trade name, Viton®, and is specifically engineered for creating a static seal on straight thread tube fittings in high-temperature system bosses. Its 75 durometer hardness provides an optimal balance of sealing force and material compliance for standard pressure applications.

The defining characteristic of this O-ring is its exceptional thermal stability, allowing it to maintain a reliable seal in continuous service temperatures up to 400°F (204°C). The AS568-018 size is designed for use with -10 (5/8 inch) tube fittings. This makes it the mandated sealing solution for major fluid connections in and around the engine compartment, firewall, and other high-temperature zones where a standard Nitrile (NBR) O-ring would rapidly degrade and fail.

Key Features

• High-Temperature Fluorocarbon (FKM): Fabricated from a Viton® or equivalent FKM elastomer, providing a continuous service temperature rating of up to 400°F (204°C).

• Designed for -10 Boss Seals: Specifically sized (AS568-018) for static axial sealing of -10 size straight thread tube fittings in their corresponding ports (bosses).

• Excellent Fluid Resistance: Offers superior chemical resistance to a wide range of petroleum-based and synthetic lubricating oils, hydraulic fluids, and jet fuels.

• 75 Durometer Hardness: The 75 Shore A hardness provides an excellent balance of sealing force and resistance to deformation for standard pressure applications.

• Aerospace Standard AS3209: Meets all dimensional, material, and quality requirements of AS3209, ensuring airworthiness and interchangeability.

• Material Identification: Typically brown in color to visually distinguish it from black Nitrile (NBR) O-rings, preventing incorrect installation.

Technical Specifications

• Part Number: AS3209-018

• Component Type: Preformed O-Ring Packing, Boss Seal

• Governing Specification: AS3209

• Material: Fluorocarbon Elastomer (FKM / Viton®)

• Hardness: 75 ± 5 Durometer Shore A

• Color (Typical): Brown

• Dimensions (AS568-018):

  • Inside Diameter (ID): 0.739 inches

  • Cross-Section (CS): 0.070 inches

• Typical Temperature Range: -15°F to +400°F (-26°C to +204°C)

Aircraft Compatibility

The AS3209-018 is a standard hardware component used across the entire aerospace industry in high-temperature fluid systems. It is not specific to one aircraft but is a fundamental component found on:

• Military Fighter, Transport, and Rotorcraft

• Commercial and Transport Category Airliners (Boeing, Airbus)

• Business and Corporate Jets (Textron Aviation, Bombardier, Gulfstream)

• High-Performance General Aviation Aircraft

Note: Verification of applicability is the responsibility of the installer. Always consult the current version of the aircraft or engine's Illustrated Parts Catalog (IPC) to confirm part number eligibility.

Applications

• Sealing of -10 size (7/8-14 thread) straight thread tube fittings on firewall-forward components.

• Connections on main hydraulic system lines.

• Large-diameter fuel and oil line connections on engine accessories.

• Any major fluid system application where operating temperatures exceed the ~250°F limit of standard Nitrile (NBR) O-rings.

Why Choose AS3209-018?

The selection of the correct elastomer for the operating environment is a flight-critical decision. Substituting a standard black Nitrile (NBR) O-ring in a location specified for a brown Fluorocarbon (FKM) O-ring will result in the seal hardening, cracking, and failing from thermal degradation. This will cause a leak of hot, flammable fluid in a critical area of the aircraft. Using a certified AS3209-018 O-ring is the only way to guarantee you are installing the correct, high-temperature material required for a safe and airworthy repair.

A critical aspect of airworthiness for an elastomeric seal like the AS3209-018 is its finite shelf life, which is determined by its cure date. Aerospace standard ARP5316 provides the guidelines for the storage and age control of aerospace elastomers. An O-ring is not an inert piece of hardware; its polymer structure is subject to slow, irreversible chemical changes over time from exposure to oxygen, ozone, and UV light, even in storage. These changes cause the material to harden, lose its elasticity, and develop a higher compression set. For this reason, every certified aerospace O-ring is marked on its packaging with the quarter and year it was vulcanized (cured). A mechanic must verify that the O-ring is within its specified shelf life (e.g., 10-15 years for FKM, depending on storage conditions) before it can be legally installed. Installing an expired O-ring, even if it appears new, introduces a significant risk of premature seal failure.

Note: This component has a finite shelf life defined by standards like ARP5316. The cure date marked on the packaging must be verified prior to installation. It is a single-use part; a new O-ring must be used every time a fitting is reinstalled. The port and fitting sealing surfaces must be impeccably clean and free of scratches or damage. The O-ring must be lubricated with clean system fluid before installation.

Documentation

The base standard for this part is the Aerospace Standard AS3209. This is a controlled document managed by SAE International. OEM-specific application and installation data is contained within the aircraft's maintenance and parts manuals.