MS28777-4 - Textron Aviation OEM Ring

MS28777-4 – Textron Aviation OEM Ring

Available now on the Airparts.aero Marketplace.

Overview

The MS28777-4 is a military-standard, single-turn, scarf-cut backup ring, an essential component for high-pressure hydraulic and pneumatic sealing applications. This is not a primary seal, but a precision-engineered support ring designed to be installed in a gland adjacent to an elastomeric O-ring. Manufactured from a high-compressive-strength Polytetrafluoroethylene (PTFE), commonly known as Teflon®, its sole function is to prevent the O-ring from extruding into the clearance gap under high pressure. Specified for use by Textron Aviation, the MS28777-4 is critical for ensuring the longevity and reliability of seals in landing gear, actuators, and other high-pressure systems.

Key Features

• Prevents O-Ring Extrusion: Its primary function is to provide mechanical support to a softer rubber O-ring. It physically blocks the clearance gap between mating parts, preventing the O-ring from being forced, or "extruded," into this gap under high pressure, which is a primary cause of seal failure.
• High-Grade PTFE Construction: Fabricated from virgin TFE (Teflon®). This material is chosen for its extremely low coefficient of friction, excellent chemical inertness, wide temperature range, and high compressive strength, ensuring it does not deform under pressure.
• Scarf-Cut Design: Features a single, angled "scarf cut." This split design allows the ring to be easily installed by expanding or twisting it over a shaft or into a bore without being permanently deformed, which is impossible with a solid ring.
• Extends System Pressure Limits: The use of backup rings allows a standard O-ring to safely operate at significantly higher pressures than it could alone, enhancing the performance and safety margin of the entire hydraulic system.
• MS Certified Standard: As a certified Military Standard part, it guarantees the material composition, dimensional accuracy, and quality required for use in certified high-pressure aerospace systems.

Technical Specifications

• Standard: MS28777 (Ring, Back-Up, TFE)
• Full Part Number: MS28777-4
• Component Type: Scarf-Cut TFE Backup Ring
• Material: Polytetrafluoroethylene (PTFE / Teflon®)
• Color: White
• Application: For use with O-rings in the AS568 dash size range of -004 through -012.
• Nominal Size: Corresponds to a 1/4 inch nominal tube fitting size.

Aircraft Compatibility

The MS28777-4 is a universal hardware component used across all categories of aircraft, including Textron Aviation platforms, wherever a backup ring is required for a small-diameter, high-pressure O-ring seal.

• Common System Applications:
  • High-Pressure Hydraulic Systems: Used in landing gear actuators, brake system components, and flight control actuators.
  • Pneumatic Systems: Installed in high-pressure pneumatic components and valves.
  • Fuel & Oil Systems: Used in certain high-pressure fuel pump and oil system applications.

Applications

The MS28777-4 is the specified solution for ensuring seal integrity under high pressure:

• High-Pressure Static & Dynamic Sealing: Installed in a groove next to an O-ring (typically on the low-pressure side) to provide support. In reciprocating applications, two backup rings (one on each side of the O-ring) are often used.
• Component Overhaul: A mandatory replacement item during the overhaul of any high-pressure hydraulic or pneumatic component to ensure the reliability of the sealing system.

Why Choose MS28777-4?

In a 3,000 PSI hydraulic system, the O-ring is under immense stress. The MS28777-4 backup ring is the engineered component that allows it to survive. Using a genuine MS-standard backup ring ensures the part is made from pure, high-grade TFE and has the correct dimensions to properly support the O-ring without obstructing its function. An improperly sized or low-quality backup ring can be ineffective or can even cause damage to the O-ring. For the reliability of flight-critical high-pressure systems, trust only certified hardware.

Order Your MS28777-4 Backup Rings Now

Enhance the reliability and pressure capability of your aircraft's sealing systems with certified MS-standard components. Visit Airparts.aero to order your MS28777-4 TFE backup rings today.

The MS28777-4 backup ring is a simple but elegant solution to the problem of O-ring extrusion. An O-ring seals by being compressed into a gland, but under high pressure, the elastomer behaves like a very thick fluid and will try to flow into any available path. The path of least resistance is the small "extrusion gap" that exists between the moving piston and the stationary cylinder wall. The MS28777-4, being made of hard, high-compressive-strength TFE, is installed in the gland on the low-pressure side of the O-ring. When pressure is applied, the O-ring is pushed against the backup ring. The backup ring is strong enough to resist deformation and physically blocks the extrusion gap. This contains the O-ring within its gland, allowing it to maintain its seal at pressures that would otherwise cause it to be nibbled away and destroyed.

NOTES

MATERIAL COMPOSITION LEATHER NO SHELF LIFE REQUIRED

Applicable Textron Aircraft

• 1900 Airliner
• 1900C Airliner
• 1900D Airliner
• Beechjet 400/400A
• King Air 350 or 350C FM-1 to FM-35
• King Air 360, 350i or 350C FM-36 & on
• King Air B200, B200T, B200C or B200CT
• King Air B200GT or B200CGT

List not comprehensive, may be applicable on other models.

Note: This is a flight-critical sealing component. Always verify the correct backup ring part number for the specific O-ring and gland size from the applicable component maintenance manual (CMM). The scarf cut should be installed away from any sharp edges. The ring is designed to be in the gland with the O-ring; it is not a washer.