MS9388-009 - Fluorocarbon 75 Durometer O-Ring

MS9388-009 – Fluorocarbon (FKM/Viton®) 75 Durometer O-Ring

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The MS9388-009 is a high-performance, preformed O-ring packing manufactured in strict accordance with Military Standard MS9388. This component is specified for use in demanding aerospace fluid systems where seals are exposed to aggressive chemicals and high temperatures. It is fabricated from a 75 durometer Fluorocarbon (FKM) elastomer, commonly known by the trade name Viton®, a material renowned for its exceptional chemical resistance and thermal stability.

This O-ring is the industry standard for sealing applications involving phosphate ester-based hydraulic fluids (e.g., Skydrol®), synthetic turbine engine oils, and jet fuels. Its material composition is specifically engineered to resist swelling, hardening, and degradation in these harsh environments where a standard Nitrile (Buna-N) O-ring would rapidly fail. The MS9388 specification guarantees that the O-ring meets the stringent requirements for material, dimensional tolerance, and quality control required for flight-critical applications.

Key Features

• Military Standard (MS) Certified: Manufactured to the exact material, hardness, and dimensional tolerances of the MS9388 specification, ensuring reliable sealing performance.

• Fluorocarbon (FKM/Viton®) 75 Durometer Material: The specified elastomer provides superior resistance to aggressive fluids, including phosphate ester hydraulics, jet fuels, and synthetic oils.

• Excellent High-Temperature Stability: Maintains sealing integrity and physical properties at continuous operating temperatures up to 400°F (204°C).

• Low Compression Set: Exhibits excellent resistance to taking a permanent set after being compressed at high temperatures, ensuring a reliable, long-lasting seal.

• Superior Chemical Resistance: Provides a reliable seal in chemical environments that would cause rapid degradation of general-purpose elastomers.

Technical Specifications

• Part Number: MS9388-009

• Supersceded by: M83248/1-009

• Component Type: Preformed Packing, O-Ring

• Governing Specification: MS9388

• Material: Fluorocarbon Rubber (FKM), Viton®.

• Hardness: 75 Durometer Shore A.

• Size (AS568A Dash Number): -009

• Dimensions:

  • Inside Diameter: 0.198 inches (5.03 mm)

  • Cross-Section: 0.070 inches (1.78 mm)

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

Aircraft Compatibility

The MS9388-009 is a standard hardware component used in countless high-temperature and aggressive fluid system applications across all categories of aircraft, particularly transport category and high-performance aircraft. It is not specific to any one airframe but is called for by part number in the maintenance and parts manuals for numerous systems and components.

Crucial Note: The correct part number for a specific application must be verified against the Illustrated Parts Catalog (IPC) or Component Maintenance Manual (CMM) for the component or aircraft being serviced.

Applications

The MS9388-009 is the specified O-ring for sealing in high-temperature and aggressive fluid environments. Common applications include:

• Phosphate Ester (Skydrol®) Hydraulic Systems: Used in actuators, valves, pumps, and fittings.

• Turbine Engine Fuel Systems: Sealing in fuel control units, pumps, and filters.

• Turbine Engine Lubrication Systems: Sealing in high-temperature oil system components.

• Firewall-Forward Fluid Connections.

Why Choose MS9388-009?

Choosing a genuine MS9388-009 O-ring is a critical decision for system safety and reliability. Fluid and elastomer compatibility is a fundamental principle of aircraft maintenance. Installing an incorrect O-ring material, such as a Nitrile (Buna-N) seal in a Skydrol® hydraulic system, will result in rapid, catastrophic failure of the seal, leading to a major hydraulic leak and potential loss of system function. The MS9388 standard guarantees the correct Fluorocarbon (FKM) material and the quality control required for a safe, durable, and reliable seal in these chemically aggressive and high-temperature environments.

The exceptional chemical and thermal stability of the MS9388 Fluorocarbon (FKM) O-ring is derived from the molecular structure of the fluoropolymer from which it is made. Its robustness comes from the immense strength of its carbon-fluorine (C-F) bonds, which are among the strongest single bonds in organic chemistry. During polymerization, fluorine atoms, which are highly electronegative, form a protective, non-reactive sheath around the vulnerable carbon backbone of the polymer chain. This fluorine sheath effectively shields the polymer's backbone from chemical attack by aggressive fluids like aromatic hydrocarbons (in jet fuel) and phosphate esters (in Skydrol®), which would readily break down the less-robust carbon-hydrogen bonds found in general-purpose elastomers like Nitrile. This same C-F bond strength is also the source of FKM's high-temperature resistance, as it requires significantly more thermal energy to induce molecular scission and degradation compared to other elastomers.

Note: O-rings are typically considered single-use components in aerospace applications. These components have a finite shelf life (cure date) which must be strictly observed. EXTREME CAUTION must be exercised to ensure the correct elastomer type is used for the system fluid. Never install a Nitrile (typically black) O-ring where a Fluorocarbon (typically brown, but color is not a reliable indicator) O-ring is specified. Installation must be performed by a certified A&P mechanic in accordance with the applicable maintenance manual.

Documentation

The definitive technical requirements for this component are detailed in Military Standard MS9388. These proprietary documents must be sourced directly from the relevant standards organizations for complete engineering specifications.