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AS1895/23-300 – SAE Standard Flared Tube Fitting Seal Assembly
Available now on the Airparts.aero Marketplace.
Overview
The AS1895/23-300 is a high-reliability, composite seal assembly manufactured in accordance with SAE Aerospace Standard AS1895, Sheet 23. This is not a standard O-ring; it is a sophisticated flare gasket specifically engineered to dramatically improve the sealing integrity of standard AN/MS 37-degree flared tube fittings. A conventional flared fitting relies on a fragile, metal-to-metal line of contact to create a seal, which is highly susceptible to leaks caused by scratches, imperfections, or slight misalignments. The AS1895/23 seal assembly is the definitive engineering solution to this problem.
The seal consists of a precision-formed metal retainer (or washer) with a chemically bonded elastomeric seal on its inside diameter. It is designed to be installed on the tube, behind the flare. When the fitting's B-nut is tightened, the metal retainer precisely centers and contains the elastomeric element, which is compressed against the flared tube surface and the fitting's cone. This creates a positive, contained, and highly reliable seal that is far superior to and more forgiving than the original metal-to-metal connection, virtually eliminating the risk of fluid leaks.
Key Features
SAE Aerospace Standard Part: Manufactured and tested to the stringent requirements of AS1895, guaranteeing performance and quality.
Composite Metal/Elastomer Design: Combines a rigid metal retainer with a soft, conformable elastomer seal for a robust and highly effective sealing solution.
Eliminates Leaks in Flared Fittings: The elastomeric element conforms to minor surface imperfections on the flare and fitting cone, creating a zero-leak, gas-tight seal.
Positive, Contained Seal: The metal retainer prevents the elastomer from being over-compressed or extruded under high pressure, ensuring a durable and reliable seal.
Vibration Resistant: Provides a more resilient seal than a simple metal-to-metal connection, making it ideal for high-vibration environments such as engine installations and helicopter applications.
Technical Specifications
Part Number / Specification: AS1895/23-300
Component Type: Seal Assembly, Flared Tube Fitting ("Flare Gasket")
Governing Specification: SAE AS1895/23
Size Code (-300): A specific size and material code that must be matched to the application's engineering drawing or maintenance manual.
Retainer Material: Typically Aluminum Alloy (for use with aluminum fittings) or CRES (for use with steel fittings) to prevent galvanic corrosion.
Elastomer Material: Varies by application. Typically Fluorocarbon (FKM/Viton®) for fuel and petroleum-based hydraulic systems, or Ethylene Propylene (EPDM) for phosphate-ester hydraulic systems (Skydrol).
Aircraft Compatibility
Universal Aerospace Application: This is a standard seal design used on any aircraft that employs AN/MS 37-degree flared tube fittings, especially in critical, high-pressure, or high-vibration systems. It is found on aircraft from:
Textron Aviation, Boeing, Airbus, Lockheed Martin, Bombardier, Gulfstream, and others.
Bombardier Global 7500
Note: The correct size and, most critically, the correct elastomer material must be verified against the specific aircraft or component maintenance manual.
Applications
High-Pressure Hydraulic Systems: Provides a leak-free seal for 3,000 PSI hydraulic lines in flight control and landing gear systems.
Fuel Systems: Ensures the integrity of fuel line connections from the tanks to the engine, eliminating a primary fire hazard.
Pneumatic and Bleed Air Systems: Used with high-temperature compatible elastomers to seal pneumatic ducting.
Oxygen Systems: Used with specific, oxygen-compatible elastomers to ensure the purity and integrity of oxygen lines.
Why Choose AS1895/23-300?
A weeping or leaking B-nut fitting is a common nuisance and a serious safety hazard. A fuel or hydraulic fluid leak presents a catastrophic fire risk. The AS1895/23-300 is a low-cost, engineered upgrade that provides a massive increase in the reliability of a standard flared fitting. By replacing the unforgiving metal-to-metal seal with a contained, conformable elastomeric seal, it provides a "zero-leak" solution that adds a significant margin of safety to any fluid system. For any critical fluid connection, especially in a high-vibration environment, the use of a certified AS1895/23 seal is a mark of superior maintenance and a direct investment in safety.
The engineering principle that makes the AS1895/23 seal superior is the transformation of the sealing mechanism from line-contact Hertzian stress to a surface-area compression seal. A standard flare fitting relies on creating an extremely high stress (Hertzian contact stress) along a microscopic line of contact to locally deform the metal, creating a seal. This makes the joint highly intolerant of any surface scratch, debris, or misalignment. The AS1895/23 seal fundamentally changes this. It introduces a soft elastomeric element with a low modulus of elasticity. This element is compressed over a much larger surface area, and it easily deforms to fill any microscopic imperfections on the flare or the fitting cone. This creates a highly reliable, zero-leak barrier at a much lower and more evenly distributed contact stress. The outer metal retainer is critical, as it supports the elastomer, preventing it from extruding or "nibbling" away under high pressure, thus combining the reliability of a soft seal with the durability of a hard fitting.
Note: The AS1895/23-300 is a flight-critical seal. It must be installed by a certified A&P mechanic. It is absolutely essential that the elastomer material is correct for the fluid in the system (e.g., FKM for fuel, EPDM for Skydrol). The seal must be installed in the correct orientation. All sealing surfaces must be clean and free of scratches or damage. The fitting's B-nut must be torqued to the value specified in the maintenance manual.
Documentation
SAE AS1895/23: The Aerospace Standard document defines all dimensional, material, and performance requirements for this series of seals and is available through SAE International and other standards providers.
