AS3209-014 – Fluorocarbon (Viton®) Boss Seal O-Ring, 75 Durometer
Available now on the Airparts.aero Marketplace.
Overview
The AS3209-014 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 AS568-014 size is designed for use with -8 (1/2 inch) tube fittings. This makes it the mandated sealing solution for larger 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 -8 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: AS3209-014
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 (AS568-014):
Inside Diameter (ID): 0.424 inches
Cross-Section (CS): 0.070 inches
Typical Temperature Range: -15°F to +400°F (-26°C to +204°C)
Aircraft Compatibility
The AS3209-014 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 -8 size (3/4-16 thread) straight thread tube fittings on firewall-forward components.
Connections on engine accessories such as fuel control units, oil filter housings, and hydraulic pumps.
Main 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 AS3209-014?
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 AS3209-014 O-ring is the only way to guarantee you are installing the correct, high-temperature material required for a safe and airworthy repair.
An important consideration for elastomeric seals in high-pressure systems is their resistance to Explosive Decompression (ED). This phenomenon occurs when high-pressure gas permeates the molecular structure of an elastomer. If the external system pressure is suddenly released, the gas trapped inside the elastomer expands rapidly, which can cause blisters, cracks, or complete rupture of the seal from the inside out. While standard Fluorocarbon (FKM) compounds like that used in the AS3209-014 offer moderate ED resistance, it is a key parameter that differentiates aerospace-grade materials from commercial ones. The manufacturing of a certified FKM O-ring involves high-purity polymers and curing processes that create a dense, low-permeability molecular structure. This minimizes the amount of gas that can be absorbed, thereby improving the seal's resilience to damage from sudden pressure changes, a condition that can be encountered in hydraulic accumulator or pneumatic system operation.
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.