MS28775-015 - Military Standard Synthetic Rubber Hydraulic O-Ring Packing Seal

MS28775-015 – Military Standard Nitrile (Buna-N) Hydraulic O-Ring Packing

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Overview

The MS28775-015 is a flight-critical, military standard O-ring packing engineered for sealing applications within aircraft hydraulic systems. Manufactured from a specific Nitrile Butadiene Rubber (NBR), or Buna-N, compound, this component is designed to provide a positive, leak-free seal against petroleum-based hydraulic fluids, including MIL-H-5606 and its modern derivatives. Its formulation and dimensions are strictly controlled by the MS28775 military specification, ensuring consistent material properties, dimensional accuracy, and reliable performance across a wide operational temperature range from -65°F to +275°F.

As an AS568 standard size -015 O-ring, this packing is utilized in countless static and dynamic sealing applications, from hydraulic line fittings to actuator pistons. The inherent properties of the NBR elastomer provide excellent resistance to abrasion, compression set, and degradation from hydrocarbon fluids. The integrity of an aircraft's hydraulic system is paramount for flight control and safety; utilizing a certified MS28775-015 O-ring ensures that the component meets the rigorous quality and traceability standards demanded for airworthy installations.

Key Features

• Military Specification Compliance: Manufactured in strict accordance with MS28775, guaranteeing material composition, dimensional tolerances, and quality.

• High-Performance Nitrile Compound: Formulated from a specific Nitrile (Buna-N) elastomer for superior resistance to petroleum-based hydraulic fluids, oils, and greases.

• AS568 Standard Sizing: Conforms to the AS568-015 dimensional standard for universal compatibility in glands designed for this size.

• Wide Temperature Range: Engineered to maintain sealing integrity and elasticity in extreme thermal conditions ranging from -65°F to +275°F (-54°C to +135°C).

• Excellent Physical Properties: Offers a high tensile strength and excellent resistance to abrasion and compression set, ensuring a durable seal in both static and dynamic applications.

• Positive Sealing Design: Provides a reliable seal under both low and high-pressure conditions, energized by the hydraulic system's operating pressure.

Technical Specifications

• Part Number: MS28775-015

• Component Type: Hydraulic O-Ring Packing Seal

• OEM Manufacturer: Manufactured to Qualified Products List (QPL) standards.

• Material: Nitrile Butadiene Rubber (NBR), Buna-N, 75 Durometer Shore A (Typical).

• Finish: N/A

• Dimensions (AS568-015):

  • Inside Diameter (ID): 0.551 inches (14.00 mm)

  • Cross-Section Diameter (CS): 0.070 inches (1.78 mm)

• Operational Temperature Range: -65°F to +275°F (-54°C to +135°C)

• Compatible Fluids: MIL-H-5606, MIL-PRF-83282, MIL-PRF-87257, and other petroleum-based hydrocarbon fluids.

• Governing Specifications: MS28775, AS568

• Certification: Shipped with a Certificate of Conformance to MS28775.

Aircraft Compatibility

The MS28775-015 is a standard hardware component used across a vast array of military, commercial, and general aviation aircraft that utilize petroleum-based hydraulic systems. It is not specific to a single aircraft model but rather to the system's fluid type and operating parameters. Common platforms include:

• Legacy military fighter, bomber, and transport aircraft

• Various rotorcraft models

• General aviation piston and turboprop aircraft

• Associated hydraulic ground support equipment

Note: Verification of applicability is the responsibility of the installer. Always consult the current version of the aircraft or component's Illustrated Parts Catalog (IPC) and maintenance manual to confirm part number eligibility.

Applications

• Static Sealing: Sealing flanges, tube fittings (AN/MS fittings), plugs, and hydraulic component housings.

• Dynamic Sealing (Reciprocating): Piston and rod seals in low-to-medium pressure hydraulic actuators for systems like landing gear, flaps, and flight controls.

• Valve Sealing: Used in various hydraulic selector valves, relief valves, and check valves.

Why Choose MS28775-015?

In hydraulic systems, the difference between a certified MS28775 O-ring and a generic commercial equivalent is the margin between dispatch reliability and catastrophic failure. This military standard component guarantees the correct elastomeric polymer, durometer, and dimensional tolerances required to withstand system pressures and temperature cycles. Using a non-traceable, uncertified part introduces unacceptable risk of material incompatibility, leading to swelling, hardening, or chemical degradation, which directly results in leaks, loss of hydraulic pressure, and potential loss of aircraft control.

The MS28775-015's function is governed by the principles of elastomeric sealing and materials science. The Nitrile Butadiene Rubber (NBR) specified is a synthetic copolymer derived from the emulsion polymerization of acrylonitrile and 1,3-butadiene. The acrylonitrile monomer provides the polar nitrile groups (-C≡N) which are key to its performance; these groups impart a strong resistance to non-polar solvents like petroleum-based hydraulic fluids, preventing the elastomer from swelling or degrading. The sealing mechanism itself is a function of engineered deformation. The O-ring, an elastomeric torus, is installed in a precisely machined groove (gland) where it is subjected to diametrical compression (squeeze). This initial squeeze creates a baseline sealing stress. When hydraulic pressure is introduced, Pascal's Law dictates that this pressure is exerted uniformly across the O-ring's exposed surface. This fluid pressure forces the elastomer against the opposing surfaces of the gland, dynamically increasing the sealing stress to a level greater than the contained pressure, thereby maintaining a positive seal across a wide pressure range.

Note: This component is a flight-critical seal and is subject to a finite shelf life as defined by aerospace standard ARP5316. Always verify the cure date of the O-ring prior to installation. It is considered a single-use part in all dynamic and critical static applications. Installation must be performed by a certified mechanic in a clean environment. Use of the system's specified hydraulic fluid as a lubricant is required, and care must be taken to avoid nicking, cutting, or twisting the O-ring during installation.

Documentation

The military standard governing this part is publicly available through the Department of Defense ASSIST database.

• ASSIST Document Summary Page for MS28775: http://quicksearch.dla.mil/qsDocDetails.aspx?ident_number=45248