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MS9386-015 – Sealed Preformed AMS7276 O-Ring
Available now through the AirParts Aero marketplace.
Overview Section
The MS9386-015 is a high-performance Fluorocarbon (FKM) O-ring designed for critical sealing applications in aerospace environments. Manufactured to the MS9386 military specification and utilizing AMS7276 (Viton™) material, this seal is engineered specifically for high-temperature resistance and compatibility with aggressive aerospace fluids, including synthetic engine oils and various fuels.
The -015 dash number corresponds to a specific size within the standard aerospace O-ring chart. Unlike general-purpose industrial seals, the MS9386-015 undergoes rigorous quality control to ensure uniform density and the absence of surface imperfections that could lead to "bypass" leaks in high-pressure turbine or hydraulic systems.
Key Features Section
AMS7276 Material (Fluorocarbon): Provides exceptional resistance to high-heat degradation and chemical swelling. It is the preferred material for "hot-side" engine seals.
Temperature Range: Capable of maintaining a flexible, airtight seal in temperatures ranging from -10°F to +400°F (-23°C to +204°C).
Chemical Compatibility: Highly resistant to MIL-PRF-23699 (Synthetic Turbine Oil), MIL-DTL-83133 (Jet A/JP-8), and standard petroleum-based lubricants.
Precision "000" Series Sizing: Part of the small-diameter series, commonly used for sealing small fluid ports, bolt heads, and instrument fittings.
Low Compression Set: Engineered to "bounce back" after prolonged compression, preventing leaks that occur during the thermal contraction of cold-soak at altitude.
Individually Sealed: Each O-ring is typically packaged in an opaque, airtight UV-protective bag to prevent ozone cracking and extend shelf life.
Technical Specifications Section
| Specification | Detail |
| Part Number | MS9386-015 |
| Material Standard | AMS7276 (Fluorocarbon / FKM) |
| Inside Diameter (ID) | 0.551 in (Nominal) |
| Cross-Section (W) | 0.070 in (Nominal) |
| Hardness | 70-80 Shore A Durometer |
| Color | Black (Standard for AMS7276) |
| Application | High-Temp Static/Dynamic Sealing |
Aircraft Compatibility Section
The MS9386-015 is a versatile seal found in both airframe and powerplant systems:
Turbine Engines: Used in oil scavenge lines and fuel nozzle interfaces for Pratt & Whitney, GE, and Rolls-Royce engines.
Hydraulic Systems: Ideal for sealing fittings in high-temp zones where Nitrile (Buna-N) would fail.
Fuel Systems: Frequently found in fuel quantity transmitters and selector valve assemblies.
Auxiliary Power Units (APU): A common seal for external plumbing on Honeywell and Hamilton Sundstrand APUs.
Technical Applications & Safety
The effectiveness of an O-ring depends on the "squeeze" or interference fit within its gland. If a gland is too deep, the MS9386-015 will not compress enough to seal; if it is too shallow, the O-ring may be pinched or sheared during assembly.
Safety Warning: Identify the Material Correcty. While the MS9386-015 looks similar to the MS29513 (Nitrile) O-ring, they are not interchangeable. Installing a Nitrile O-ring in a high-heat zone meant for Fluorocarbon (AMS7276) will cause the seal to turn brittle and "glassify," leading to a sudden and total seal failure. Always verify the MS number on the packaging before breaking the seal.
Technical Engineering Insight
The engineering value of the MS9386-015 lies in its Chemical Permeability Resistance. In turbine oil systems, the fluid is not only hot but also contains acidic by-products.1 The AMS7276 compound is formulated to resist "sour" oil degradation, which would otherwise swell a standard rubber seal and block fluid flow. This material's ability to maintain its Durometer (Hardness) under heat ensures that it does not "extrude" into the gaps between metal parts under high pressure.
Installation & Maintenance Addendum
Check for Crazing: Before installation, gently stretch the O-ring and inspect it under a 10x magnifying glass for tiny cracks (crazing). If any are found, the O-ring has been exposed to ozone and is unairworthy.
Lubrication: Use a light coating of the system fluid or a dedicated O-ring lubricant (like Parker O-Lube) to ensure the seal slides into the gland without twisting. A "spiraled" O-ring is a common cause of leaks in dynamic assemblies.
Shelf Life: AMS7276 has a theoretically "unlimited" shelf life if kept in its original packaging, but many maintenance manuals require disposal after 15 years from the cure date.
