AIRCRAFT HARDWARE
Essential Components for Safe Flight
Aircraft hardware forms the critical foundation of every aircraft structure. From the smallest rivet to specialized fasteners, these components ensure the integrity and safety of the aircraft. This presentation explores the various types of hardware used in aircraft construction and maintenance, their proper selection, installation, and safety methods.
PACKINGS: SEALING CRITICAL SYSTEMS
Packings are made of synthetic or natural rubber and serve as "running seals" in units with moving parts, such as:
Selector Valves
Actuating Cylinders
Pumps
O-RING PACKINGS: VERSATILE SEALING SOLUTIONS
O-ring packings prevent both internal and external leakage and are themost commonly used type. They seal effectively in both directions,making them versatile for various applications.
For installations subject to pressures above 1,500 psi, backup rings areused with O-rings to prevent extrusion. When pressure comes fromboth sides, two backup rings must be used (one on either side of theO-ring). With pressure from only one side, a single backup ring isplaced on the side away from the pressure.
O-rings are manufactured from materials specifically compounded forvarious operating conditions, temperatures, and fluids. An O-ringdesigned for static (stationary) seals may not perform properly wheninstalled on moving parts like hydraulic pistons.
EVOLUTION OF O-RING TECHNOLOGY
Advances in aircraft design have necessitated new O-ring compositions to meet changing operating conditions:
MS28775 Series
Original Hydraulic O-rings
High-Temperature Development
O-RING IDENTIFICATION SYSTEMS
Manufacturers provide color-coding on some O-rings, but this is nota reliable or complete means of identification. The color-codingsystem identifies:
Limitations of Color-Coding
Color-Coding System Identifies
- Coding on some rings is not permanent
- System fluid or vapor compatibility
- May be omitted due to manufacturing difficulties
- In some cases, the manufacturer
- Provides no means to establish the age of the O-ring
Color codes for MIL-H-5606 fluid always contain blue but may also include red or other colors. The most reliable identification is the basic part number on the sealed envelope in which O-rings are packaged.
- Does not indicate temperature limitations
O-RING INSPECTION
Proper inspection of O-rings is critical before installation. Even slight surface flaws can prevent satisfactory O-ring performance undervariable operating pressures of aircraft systems.
Visual Inspection
Use a 4-power magnifying glass with adequate lighting to inspect each ring for surface flaws that could affect performance.
Stretching Test
Slightly stretch the ring by rolling it inside out to reveal defects not otherwise visible.
Inner Surface Check
Roll the ring on an inspection cone or dowel to check the inner diameter surface for small cracks, foreign material, or irregularities.
BACKUP RINGS: SUPPORTING O-RING PERFORMANCE
Backup rings (MS28782) made ofTeflon™ provide critical support to O-rings in high-pressure applications.They offer several advantages:
Backup ring dash numbers indicate not only their size but also directly to the dash number of the O-ring they support. They are interchangeable if they have the proper overall dimension to support the applicable O-ring. Backup rings are not color-coded or marked and must be identified from package labels.
- Do not deteriorate with age
- Unaffected by any system fluid or vapor
- Can tolerate temperature extremes beyond those encountered in high-pressure hydraulic systems
BACKUP RING INSPECTION
Proper inspection of backup rings should include checking the following:
Scarf Cuts
Spiral Integrity
Edge Condition
Surface Quality
V-RING (AN 6225)
U-RING (AN 6226)
- One-way seals installed with the open end of the “V” facing the pressure
- Used in brake assemblies and brake master cylinders
- Require male and female adapters to hod them in proper position
- Seal pressure in only one direction
- Primarily low-pressure packings for presures less than 1,000 psi
- Lip must face toward the pressure
- Torque the seal retainer to the manufacturer’s specifications for proper service
GASKETS: STATIC SEALING SOLUTIONS
Gaskets are used as static (stationary) seals between two flat surfaces. Common gasket materials include:
Asbestos
Copper
Cork
Rubber
WIPERS: PROTECTING MOVING COMPONENTS
Critical functions of wiper seals
Types of wiper seals
Copper
Solid copper washers are used for spark plug gaskets where a non-compressible, yet semi-soft gasket is essential.
Asbestos
Used wherever a heat-resistant gasket is needed, especially for exhaust systems. Most asbestos exhaust gaskets have a thin sheet of copper edging to prolong their life.
Cork
Used as an oil seal between the engine crankcase and accessories, and where a gasket must occupy an uneven space caused by rough surfaces or expansion and contraction.
Rubber
Used where a compressible gasket is needed, but should not be used where it may contact gasoline or oil as rubber deteriorates rapidly when exposed to these substances.
O-Rings.pptx
AMY SCHNEIDER
Created on September 23, 2025
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Transcript
AIRCRAFT HARDWARE
Essential Components for Safe Flight
Aircraft hardware forms the critical foundation of every aircraft structure. From the smallest rivet to specialized fasteners, these components ensure the integrity and safety of the aircraft. This presentation explores the various types of hardware used in aircraft construction and maintenance, their proper selection, installation, and safety methods.
PACKINGS: SEALING CRITICAL SYSTEMS
Packings are made of synthetic or natural rubber and serve as "running seals" in units with moving parts, such as:
Selector Valves
Actuating Cylinders
Pumps
O-RING PACKINGS: VERSATILE SEALING SOLUTIONS
O-ring packings prevent both internal and external leakage and are themost commonly used type. They seal effectively in both directions,making them versatile for various applications.
For installations subject to pressures above 1,500 psi, backup rings areused with O-rings to prevent extrusion. When pressure comes fromboth sides, two backup rings must be used (one on either side of theO-ring). With pressure from only one side, a single backup ring isplaced on the side away from the pressure.
O-rings are manufactured from materials specifically compounded forvarious operating conditions, temperatures, and fluids. An O-ringdesigned for static (stationary) seals may not perform properly wheninstalled on moving parts like hydraulic pistons.
EVOLUTION OF O-RING TECHNOLOGY
Advances in aircraft design have necessitated new O-ring compositions to meet changing operating conditions:
MS28775 Series
Original Hydraulic O-rings
High-Temperature Development
O-RING IDENTIFICATION SYSTEMS
Manufacturers provide color-coding on some O-rings, but this is nota reliable or complete means of identification. The color-codingsystem identifies:
Limitations of Color-Coding
Color-Coding System Identifies
Color codes for MIL-H-5606 fluid always contain blue but may also include red or other colors. The most reliable identification is the basic part number on the sealed envelope in which O-rings are packaged.
O-RING INSPECTION
Proper inspection of O-rings is critical before installation. Even slight surface flaws can prevent satisfactory O-ring performance undervariable operating pressures of aircraft systems.
Visual Inspection
Use a 4-power magnifying glass with adequate lighting to inspect each ring for surface flaws that could affect performance.
Stretching Test
Slightly stretch the ring by rolling it inside out to reveal defects not otherwise visible.
Inner Surface Check
Roll the ring on an inspection cone or dowel to check the inner diameter surface for small cracks, foreign material, or irregularities.
BACKUP RINGS: SUPPORTING O-RING PERFORMANCE
Backup rings (MS28782) made ofTeflon™ provide critical support to O-rings in high-pressure applications.They offer several advantages:
Backup ring dash numbers indicate not only their size but also directly to the dash number of the O-ring they support. They are interchangeable if they have the proper overall dimension to support the applicable O-ring. Backup rings are not color-coded or marked and must be identified from package labels.
BACKUP RING INSPECTION
Proper inspection of backup rings should include checking the following:
Scarf Cuts
Spiral Integrity
Edge Condition
Surface Quality
V-RING (AN 6225)
U-RING (AN 6226)
GASKETS: STATIC SEALING SOLUTIONS
Gaskets are used as static (stationary) seals between two flat surfaces. Common gasket materials include:
Asbestos
Copper
Cork
Rubber
WIPERS: PROTECTING MOVING COMPONENTS
Critical functions of wiper seals
Types of wiper seals
Copper
Solid copper washers are used for spark plug gaskets where a non-compressible, yet semi-soft gasket is essential.
Asbestos
Used wherever a heat-resistant gasket is needed, especially for exhaust systems. Most asbestos exhaust gaskets have a thin sheet of copper edging to prolong their life.
Cork
Used as an oil seal between the engine crankcase and accessories, and where a gasket must occupy an uneven space caused by rough surfaces or expansion and contraction.
Rubber
Used where a compressible gasket is needed, but should not be used where it may contact gasoline or oil as rubber deteriorates rapidly when exposed to these substances.