M25988/4-904 - Aerospace Preformed Packing O-Ring

M25988/4-904 – Aerospace Preformed Packing O-Ring

Available now on the Airparts.aero Marketplace.

Overview

The M25988/4-904 is a military-standard, preformed packing O-ring engineered for demanding aerospace applications requiring exceptional performance across a wide temperature range. This O-ring is manufactured in strict accordance with the MIL-DTL-25988 Type 4 specification, which mandates the use of a high-quality Fluorosilicone (FVMQ) elastomer. This advanced material combines the excellent low-temperature flexibility of silicone with the fuel and oil resistance of fluorocarbons, making it the ideal sealing solution for systems that experience both extreme cold and exposure to jet fuels and synthetic oils.

Key Features

• Fluorosilicone (FVMQ) Material: Fabricated from a specialized Fluorosilicone rubber. This material provides an outstanding operational temperature range and is highly resistant to swelling and degradation when exposed to jet fuels (JP-4, JP-5, JP-8), engine oils, and most hydraulic fluids.
• Exceptional Low-Temperature Flexibility: Unlike standard Viton® (FKM) O-rings, Fluorosilicone maintains its elasticity and sealing capability at extremely low temperatures, down to -100°F (-73°C), preventing leaks in high-altitude and arctic conditions.
• Mil-Spec Certified Quality: As a certified military specification part, the M25988/4-904 guarantees material traceability, dimensional accuracy, and performance characteristics that meet the highest standards for safety and airworthiness.
• Distinctive Color-Coding: The blue color of the O-ring is mandated by the M25988/4 specification, providing immediate visual confirmation that the correct, fuel-resistant, wide-temperature-range material is being used for the application.
• Precise Dimensions: The "-904" dash number corresponds to a specific dimensional standard (AS568), guaranteeing a perfect fit in glands and grooves designed for this O-ring size.

Technical Specifications

• Standard: MIL-DTL-25988/4 (also specified under SAE AS3582)
• Full Part Number: M25988/4-904
• Material: Fluorosilicone (FVMQ)
• Durometer (Hardness): 75 Shore A
• Color: Blue
• AS568 Dash Size: -904
• Nominal Dimensions:
  • Inside Diameter (I.D.): 0.351 inches
  • Cross Section (C.S.): 0.118 inches
• Operating Temperature Range: Approximately -100°F to 350°F (-73°C to 177°C)

Aircraft Compatibility

The M25988/4-904 is a specialized seal not tied to a single aircraft but is specified by engineers for use in any system where its unique material properties are required. It is commonly found in military aircraft, commercial airliners, and high-performance general aviation aircraft.

• Common Applications:
  • Fuel Systems: Seals for fuel line fittings, connectors, fuel control units (FCUs), and fuel quantity transmitters, especially in areas subject to cold-soaking.
  • Engine & APU Systems: Used as seals in lubrication and oil systems that utilize synthetic oils and experience a wide range of operating temperatures.
  • Hydraulic Systems: Utilized in specific hydraulic systems where low-temperature performance is critical.

Applications

The M25988/4-904 is the definitive choice for sealing challenges that exceed the capabilities of standard materials:

• Wide Temperature Range Sealing: Its primary application is in joints that must maintain a perfect seal from ground temperatures to the extreme cold of high-altitude flight.
• Fuel & Oil Exposure: Provides a long-lasting, reliable seal in constant contact with aggressive aviation fuels and synthetic engine oils.
• Low-Pressure Static Sealing: Ideal for creating a durable seal in static applications like flanges and connector plugs.

Why Choose M25988/4-904?

Standard O-rings made from Nitrile (Buna-N) or Fluorocarbon (Viton®) can become brittle and fail at the low temperatures encountered at high altitudes. The M25988/4-904, made from Fluorosilicone, is specifically engineered to overcome this failure mode. Using a genuine, certified Mil-Spec part is the only way to ensure the O-ring has the correct chemical composition and physical properties to prevent fuel or oil leaks, which can be catastrophic in an aviation environment. For any application specifying this part number, there is no acceptable substitute.

Order Your M25988/4-904 O-Rings Now

Ensure the integrity of your critical fuel and oil systems with a genuine Mil-Spec Fluorosilicone O-ring. Visit Airparts.aero to order your M25988/4-904 seals today.

The material science behind the M25988/4-904 O-ring is a testament to aerospace engineering. Fluorosilicone (FVMQ) is a polymer chain of silicone with fluorinated side-chains. This molecular structure gives it a unique duality: the silicone "backbone" provides the excellent thermal stability and low-temperature flexibility (-73°C) that standard fluorocarbon elastomers lack, while the fluorinated side-chains provide the chemical resistance to non-polar solvents like jet fuel, a property that standard silicone lacks. This combination makes it the optimal material choice for sealing hydrocarbon fuels in applications that are exposed to the full atmospheric temperature spectrum, from desert tarmacs to the stratosphere.

Note: Always verify the correct O-ring part number from the applicable maintenance or overhaul manual. Ensure the O-ring is within its specified shelf life before installation. Lubricate with a compatible fluid to prevent damage during assembly. The blue color is a critical identifier and should not be substituted with black or brown O-rings unless explicitly permitted by engineering documentation.