AS3209-011 - Packing Preformed Fluorocarbon O-Ring

AS3209-011 – Fluorocarbon (Viton®) Boss Seal O-Ring, 75 Durometer

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Overview

The AS3209-011 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). This makes it the mandated sealing solution for 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 Boss Seals: Specifically sized and specified under AS3209 for static axial sealing of 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: AS3209-011

• 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 (AS568-011):

  • Inside Diameter (ID): 0.299 inches

  • Cross-Section (CS): 0.070 inches

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

Aircraft Compatibility

The AS3209-011 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 straight thread tube fittings on firewall-forward components.

• Connections on engine accessories such as fuel control units, oil filter housings, and hydraulic pumps.

• Hydraulic and fuel lines located in close proximity to high-temperature bleed air ducts or exhaust components.

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

Why Choose AS3209-011?

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 AS3209-011 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 performance metric for any elastomeric seal, and a key reason for specifying Fluorocarbon (FKM) in the AS3209-011, is its low compression set. Compression set is the permanent deformation that remains in an elastomer after it has been subjected to a sustained compressive force, especially at elevated temperatures. An O-ring functions by pushing back against the surfaces it is sealing; this "push back" force is a function of its elastic properties. An elastomer with a high compression set will "forget" its original shape after a thermal cycle, losing its elasticity and its ability to exert a sealing force, resulting in a leak. FKM elastomers exhibit an exceptionally low compression set at high temperatures. This means that even after long periods of being compressed in a hot engine environment, the AS3209-011 O-ring will retain its elasticity and continue to provide the reliable sealing force required for a leak-free joint.

Note: This component has a finite shelf life defined by standards like ARP5316. The cure date 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.