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MS9386-014 – High-Temperature Silicone Rubber O-Ring
Available now through the AirParts Aero marketplace.
Overview Section
The MS9386-014 is a high-performance Silicone Rubber O-Ring manufactured to Military Standard specifications. This specialized seal is engineered for environments that demand extreme thermal stability and resistance to oxidation. Unlike standard Nitrile O-rings, the MS9386 series utilizes a silicone elastomer that remains flexible and effective at temperatures where other rubbers would become brittle or melt.
With a nominal 1/2-inch ID and a 1/16-inch cross-section, the -014 size is a common choice for static seals in engine accessories, electronic enclosures, and low-pressure air systems. Its characteristic rust-red/orange color allows for immediate identification as a high-temperature silicone component during maintenance inspections.
Key Features Section
Extreme Temperature Range: Maintains a reliable seal from -80°F to +450°F, making it ideal for engine bleed air systems and "hot-spot" accessory mountings.
Superior Ozone & UV Resistance: Highly resistant to environmental aging, weathering, and ozone attack, ensuring a long service life in exposed airframe areas.
Low Compression Set: Designed to retain its "spring-back" force over long periods of compression, preventing leaks during thermal cycling.
High Dielectric Strength: The silicone material provides excellent electrical insulation, making it suitable for sealing connectors in avionics and power distribution boxes.
Chemical Stability: Resists most common engine oils and "low-swell" fluids; however, it is specifically optimized for air, water, and specialized lubricants.
Precision Sizing: Manufactured to the -014 standard dash size for a perfect fit in standard aerospace gland designs.
Technical Specifications Section
| Specification | Detail |
| Part Number | MS9386-014 |
| Material | Silicone Rubber (AMS 3304 or equivalent) |
| Hardness | 70 Durometer (Shore A) |
| Inside Diameter (ID) | 0.489 inches (Nominal 1/2") |
| Outside Diameter (OD) | 0.629 inches (Nominal 5/8") |
| Cross Section (W) | 0.070 inches (Nominal 1/16") |
| Color | Rust-Red / Orange |
| Military Standard | MS9386 (Supersedes AS9386) |
Aircraft Compatibility Section
The MS9386-014 is a vital sealing component found in various high-heat areas across the AirParts Aero inventory:
Turbine Engine Accessories: Used in the mounting flanges of oil scavenge pumps and alternator drives on Pratt & Whitney PT6A and Honeywell TPE331 engines.
Bleed Air Systems: Found in the coupling seals for environmental control systems (ECS) on Beechcraft King Air and Cessna Citation aircraft.
Avionics Cooling: Utilized in the seals for pressurized avionics canisters and external sensor housings.
Fuel System Drains: Used in specific fuel bowl and drain valve assemblies where high ambient heat from the engine exhaust is present.
Technical Applications & Safety
The MS9386-014 is primarily intended for Static Seals. While silicone is exceptional at handling heat, it has lower "tear strength" and abrasion resistance than Nitrile or Fluorocarbon (Viton).2 Therefore, it is rarely used in dynamic applications (like reciprocating pistons) where the seal is subject to constant friction.
Safety Warning: Do not use MS9386 silicone O-rings in high-pressure hydraulic systems. Silicone is permeable to certain gases and can be physically "shredded" by the high-velocity fluid flow of a hydraulic system. Additionally, ensure compatibility with your specific engine oil; while silicone is resistant to many oils, some ester-based turbine oils can cause excessive swelling. Always refer to the Aircraft Maintenance Manual (AMM).
Technical Engineering Insight
The engineering value of the MS9386-014 lies in its Low-Temperature Flexibility. While many O-rings "glass out" and become hard as plastic at -40°F, silicone remains rubbery. This prevents "start-up leaks" in aircraft that have been cold-soaked at high altitudes or on Arctic ramps.
By choosing the genuine Military Standard O-ring through AirParts Aero, you ensure that the elastomer is free from the organic fillers used in "industrial" silicone, which can leach out and contaminate engine oil or fuel systems. The MS9386-014 is also "non-stick," preventing the seal from vulcanizing to the metal flange, which protects the aluminum housing from damage during the next maintenance cycle.
Installation & Maintenance Addendum
Avoid Sharp Tools: Silicone is susceptible to "notch sensitivity." A tiny nick from a metal screwdriver during installation can cause the entire O-ring to split under pressure. Use plastic installation tools.
Lubrication: Use a light coating of Dow Corning 4 (or an approved silicone-based lubricant) to aid installation. Do not use petroleum-based grease unless specifically authorized, as it can cause localized swelling.
Visual Inspection: During inspection, look for "crazing" or small cracks on the surface, which indicate the silicone has reached its thermal limit and needs replacement.
