Gasket
A resilient sealing component that prevents moisture, dust, and contaminants from entering the AGL fixture housing. Made from rubber, silicone, or other elastomeric materials, the gasket ensures the fixture maintains its IP67/IP68 ingress protection rating, safeguarding internal electronics and optics from environmental damage.
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What Is It?
A Gasket is a mechanical seal that fills the space between two or more mating surfaces in an AGL fixture, preventing the ingress of moisture, dust, and other environmental contaminants. Typically made from elastomeric materials such as silicone, EPDM (ethylene propylene diene monomer), nitrile rubber, or fluorosilicone, the gasket is compressed between the fixture's housing and its cover, lens, or cable entry to create a watertight and airtight seal. The gasket is a critical component for maintaining the fixture's IP67 (dust-tight and protected against temporary immersion) or IP68 (dust-tight and protected against continuous immersion) rating, ensuring reliable operation in the harsh outdoor airfield environment.
Purpose & Function
The gasket's purpose is the same protective function as the O-ring's, applied to flat or irregular mating surfaces rather than round bores: keeping moisture, dust, and contaminants out of an AGL fixture so its electrical and optical components keep working as intended. Because a lighting circuit's outage can take an entire string of runway or taxiway lights out of service, the gasket's seal at a cover joint, cable entry, or cabinet door is a direct line of defence against water ingress that would otherwise corrode terminals or cause electrical faults. Its function depends on being compressed to the correct percentage of its thickness — enough to seal reliably against the groove, but not so much that it damages the housing or loses its elasticity — so that the seal continues to perform through years of temperature cycling, vibration, and exposure to fuels and de-icing chemicals.
Where Is It Used?
Gaskets are used in virtually every AGL fixture and enclosure where environmental sealing is required:
- Runway Edge & Centreline Lights: Gaskets between the housing and lens/cover to prevent moisture ingress.
- Threshold & End Lights: Seals for the optical window and cable entry points.
- Taxiway Lights: Gaskets for the housing and lens assembly.
- Approach Lighting: Seals for barrette housings and cable glands.
- PAPI & VASI: Gaskets for the optical units and cable entries.
- Obstruction Lights: Seals for beacon housings and lens assemblies.
- Connectors & Cable Entries: Gaskets for cable glands and junction boxes.
- CCRs & Control Panels: Gaskets for cabinet doors and cable entries.
Installation & Location
The gasket is seated in a machined groove or against a flat mating face between the two housing halves, lens, or cover it seals, and is compressed evenly by the fastening bolts or retaining ring so it forms a continuous, unbroken seal around the full perimeter. It's fitted dry or with a thin film of compatible silicone grease (never a solvent-based adhesive, which can attack the gasket material) and is replaced, rather than reused, whenever the joint is opened for lamp changes, cleaning, or servicing, since a compressed gasket can take a permanent set and no longer seal reliably once removed. Bolt torque is applied evenly and in sequence across the joint so the gasket compresses uniformly rather than being pinched unevenly on one side and left loose on the other.
How Does It Work?
A gasket works by being compressed between two surfaces, filling the microscopic gaps and irregularities that would otherwise allow water, dust, or air to pass through. The gasket's elastomeric properties allow it to deform under pressure, creating a tight seal. The sealing effectiveness depends on several factors:
- Material: The elastomer must be resistant to the environmental conditions (UV, ozone, temperature extremes, chemicals).
- Compression: The gasket must be compressed to the correct percentage (typically 15–30% of its original thickness) to achieve an effective seal without causing stress damage to the housing.
- Groove Design: The housing must have a properly designed groove or channel that retains the gasket and provides the correct compression.
- Surface Finish: Mating surfaces must be smooth and free of burrs or damage to ensure uniform compression.
In AGL fixtures, gaskets are often combined with O-rings for rotating or threaded joints, and are designed to withstand high-pressure water jets (IP69K) in some applications.
Seal Formation Requirements & Control Logic
All four conditions have to hold together — getting three right and one wrong still lets moisture or dust through.
Physical Construction
Gaskets are die-cut or moulded to match the exact joint profile they seal — a flat ring for a top-cover-to-housing face, a flanged section for a cable gland, or a custom cut-out for an irregular mating surface. Cross-section and thickness are specified so that, once the joint is torqued to spec, the material compresses to its target percentage (typically 20–30% of free height) without over-compressing into permanent set or under-compressing and leaving a leak path. Most fixture gaskets are retained in a shallow moulded or machined groove in one of the mating faces, which keeps the gasket correctly positioned during assembly and prevents it from extruding sideways under compression. Material selection (silicone, EPDM, nitrile, or fluorosilicone) is matched to the joint's exposure — UV and ozone resistance for an externally visible seal, fuel resistance for an apron-area fixture — since the wrong elastomer can harden or swell well before its rated service life.
Technical Parameters
| Parameter | Typical Value |
|---|---|
| Material | Silicone, EPDM, Nitrile (NBR), Fluorosilicone (FVMQ), or PTFE |
| Hardness (Shore A) | 40 – 70 (depending on application) |
| Temperature Range | -40°C to +150°C (silicone), -30°C to +120°C (EPDM) |
| Compression Set (CS) | < 20% (at 150°C for 24 hours, typical) |
| Tensile Strength | 5 – 15 MPa (depending on material) |
| Elongation at Break | 200 – 800% (depending on material) |
| UV / Ozone Resistance | Excellent (silicone), good (EPDM), poor (NBR without additives) |
| Chemical Resistance | Resistant to de-icing fluids, jet fuel, hydraulic fluids (varies by material) |
| IP Rating Achieved | IP67 / IP68 (when properly designed and installed) |
Applicable Standards
IEC 60529
Degrees of protection provided by enclosures (IP code)
ASTM D2000
Standard classification system for rubber products
FAA AC 150/5345-46
Specification for Runway, Taxiway, Heliport, and Vertiport Light Fixtures — includes ingress-protection/sealing requirements for AGL fixtures
IEC 61827
Characteristics of inset and elevated AGL luminaires (environmental sealing reference)
Installation Requirements
Condition Inspection
Pre-InstallationInspect the gasket for pre-existing compression set, tears, or moulding defects before fitting to the housing.
Material Compatibility Check
Pre-InstallationConfirm the specified material (silicone, EPDM, nitrile, or fluorosilicone) matches the fixture's exposure to fuel, de-icing fluid, or UV as required before fitting.
Groove Seating
MechanicalSeat the gasket in the shallow moulded or machined groove on the mating face, keeping it correctly positioned and preventing sideways extrusion under compression.
Fastener Torque for Target Compression
MechanicalTorque joint fasteners evenly around the full perimeter to achieve the gasket's target compression (typically 20–30% of free height), avoiding over- or under-compression.
Pre-Sealing Sign-off
DocumentationRecord gasket type and batch as-built before the joint is closed up, ahead of ingress-protection testing.
Testing & Commissioning
Pre-Installation Condition Check
Pre-InstallationInspect the gasket for pre-existing compression set, tears, or moulding defects before fitting to the housing.
Material Compatibility Verification
Pre-InstallationConfirm the gasket material specified (silicone, EPDM, nitrile, or fluorosilicone) matches the fixture's exposure to fuel, de-icing fluid, or UV as required.
Seating & Compression Check
InstallationConfirm the gasket seats evenly around its full perimeter and that fastener torque achieves the correct, uniform compression.
Ingress Protection Verification
Final AcceptancePressure or water-immersion test the sealed joint to confirm the fixture's IP67/IP68 rating is achieved.
Documentation & As-Built Sign-off
Final AcceptanceRecord gasket type, batch, and IP test results in the commissioning dossier for handover.
Inspection & Maintenance
Compression Set Inspection
AnnualCheck the gasket for permanent flattening or loss of resilience that reduces its sealing force over time.
UV & Ozone Degradation Check
AnnualInspect for surface cracking or hardening caused by prolonged UV and ozone exposure.
Chemical Resistance Check
AnnualExamine the gasket for swelling or softening from de-icing fluid or solvent contact, replacing if compromised.
Seating & Installation Check
Whenever disturbedConfirm the gasket sits evenly without twisting or pinching whenever a cover or fixture it seals is opened for service.
Common Field Issues
Compression Set (Permanent Deformation)
Over time, gaskets can lose their elasticity due to thermal cycling and compression set, resulting in reduced sealing force and moisture ingress. This is a common failure mode. Regular inspection and replacement of gaskets (typically every 3-5 years) is recommended.
UV & Ozone Degradation
Gaskets exposed to direct sunlight and ozone can become brittle, crack, and lose their sealing properties. Use of UV-stabilised materials (silicone, EPDM) is essential for long-term durability in airfield environments.
Chemical Attack from De-icing Fluids
De-icing fluids (ethylene glycol, propylene glycol) and jet fuel can cause swelling or degradation of some elastomers. Always use gasket materials that are compatible with the chemicals used at the airfield.
Improper Installation (Twisting, Pinching)
If the gasket is twisted, pinched, or not seated correctly during installation, it will not seal properly. Follow the manufacturer's installation instructions carefully, and ensure the gasket is clean and free of damage before installation.
Troubleshooting Guide
Moisture Fogging or Condensation Inside the Fixture
Gasket Brittle, Cracked, or Crumbling
Gasket Swollen or Softened
Seal Fails Shortly After a Maintenance Visit
Failure Modes & Root Causes
Compression Set
UV / Ozone Embrittlement
Chemical Swelling
Installation Damage / Reuse
Safety & Operational Notes
Electrical Isolation
Electrical SafetyDe-energise and lock out the fixture circuit before opening the housing or cover to replace a gasket, since the seal sits directly against live-adjacent internal components.
Correct Seating & Compression
MechanicalSeat the replacement gasket fully in its groove without twisting or stretching, and tighten fasteners evenly to the specified pattern and torque; an unevenly compressed gasket is a common source of a re-opened leak path.
Material Compatibility
ComplianceUse only the gasket material specified for the fixture (silicone, EPDM, nitrile, or fluorosilicone as applicable); substituting an incompatible material can fail early under UV, fuel exposure, or temperature extremes.
Verify IP Rating After Reassembly
ComplianceConfirm the housing is fully closed and the seal is intact before re-energising, since a compromised gasket undermines the fixture's IP67/IP68 rating and can lead to a downstream electrical fault.
FOD Control
OperationalAccount for old gasket material, fasteners, and packaging when working in the movement area, and remove all debris before leaving the site.
PPE
Personnel SafetyUse insulated tools for any electrical connection work and standard airside PPE when working on or near an active movement area.
Restore to Compliant State
ComplianceConfirm no visible gaps, pinching, or damage to the new gasket before closing out the work and returning the fixture to service.
Engineering & Expert Notes
A Slow Ingress Fault Often Traces Back Months
TroubleshootingMoisture ingress from a degraded gasket rarely causes an immediate fault; it more commonly shows up as a gradually worsening insulation resistance reading over several maintenance cycles, so when investigating a developing electrical fault, check gasket condition even if the fixture was serviced without issue at its last visit.
Chemical Exposure Ages Seals Faster Than UV Alone
DurabilityFixtures exposed to repeated glycol-based de-icing fluid or fuel residue see accelerated gasket degradation compared to sun and weather exposure alone; specify chemical-rated material for positions near taxiway/runway intersections or apron stands, and inspect these positions on a shorter interval than fixtures in less exposed locations.
Uneven Fastener Torque Undoes a Correct Gasket
MechanicalA gasket that's the right material and correctly seated can still fail to seal if fasteners are tightened out of sequence or to uneven torque, since this can pinch or distort the seal at one point while leaving it under-compressed elsewhere; follow the specified tightening pattern rather than simply working around the housing in one pass.
Cold-Weather Installation Needs Extra Care
InstallationSome gasket materials stiffen noticeably in cold conditions, making it easier to crease or pinch the seal during installation without it being obvious at the time; take extra care seating a gasket in cold weather and consider warming the material slightly if the manufacturer permits it, rather than forcing a stiff gasket into place.
Don't Assume Generic Aftermarket Gaskets Are Equivalent
ProcurementA generically-sized aftermarket gasket can match dimensions while using a different compound than the original specification, changing its chemical resistance or temperature range without any visible difference; source replacement gaskets against the fixture manufacturer's material specification rather than dimension alone.
Check the Groove, Not Just the Gasket
MaintenanceA perfectly good new gasket can still fail to seal if the housing groove itself has developed corrosion pitting or debris buildup from the previous seal's failure; clean and inspect the groove surface whenever replacing a gasket, rather than assuming a fresh seal alone resolves a recurring leak.
Frequently Asked Questions
Short answers about the Gasket: what it is, how it works, typical specifications, standards, maintenance and common faults.
Q1What is a Gasket?
A Gasket is a mechanical seal that fills the space between two or more mating surfaces in an AGL fixture, preventing the ingress of moisture, dust, and other environmental contaminants. Typically made from elastomeric materials such as silicone, EPDM (ethylene propylene diene monomer), nitrile rubber, or fluorosilicone, the gasket is compressed between the fixture's housing and its cover, lens, or cable entry to create a watertight and airtight seal.
Q2What is the purpose of a Gasket?
The gasket's purpose is the same protective function as the O-ring's, applied to flat or irregular mating surfaces rather than round bores: keeping moisture, dust, and contaminants out of an AGL fixture so its electrical and optical components keep working as intended.
Q3Where is a Gasket used and installed?
Gaskets are used in virtually every AGL fixture and enclosure where environmental sealing is required: Runway Edge & Centreline Lights: Gaskets between the housing and lens/cover to prevent moisture ingress. Threshold & End Lights: Seals for the optical window and cable entry points. Taxiway Lights: Gaskets for the housing and lens assembly. Approach Lighting: Seals for barrette housings and cable glands. PAPI & VASI: Gaskets for the optical units and cable entries. Obstruction Lights: Seals for beacon housings and lens assemblies.
Q4How does a Gasket work?
A gasket works by being compressed between two surfaces, filling the microscopic gaps and irregularities that would otherwise allow water, dust, or air to pass through. The gasket's elastomeric properties allow it to deform under pressure, creating a tight seal. The sealing effectiveness depends on several factors: Material: The elastomer must be resistant to the environmental conditions (UV, ozone, temperature extremes, chemicals).
Q5What are the typical technical parameters of a Gasket?
Typical values are — Material: Silicone, EPDM, Nitrile (NBR), Fluorosilicone (FVMQ), or PTFE; Hardness (Shore A): 40 – 70 (depending on application); Temperature Range: -40°C to +150°C (silicone), -30°C to +120°C (EPDM); Compression Set (CS): < 20% (at 150°C for 24 hours, typical); Tensile Strength: 5 – 15 MPa (depending on material); Elongation at Break: 200 – 800% (depending on material); UV / Ozone Resistance: Excellent (silicone), good (EPDM), poor (NBR without additives); Chemical Resistance: Resistant to de-icing fluids, jet fuel, hydraulic fluids (varies by material); IP Rating Achieved: IP67 / IP68 (when properly designed and installed).
Q6Which standards apply to a Gasket?
The main references are IEC 60529 — Degrees of protection provided by enclosures (IP code); ASTM D2000 — Standard classification system for rubber products; FAA AC 150/5345-46 — Specification for Runway, Taxiway, Heliport, and Vertiport Light Fixtures — includes ingress-protection/sealing requirements for AGL fixtures; IEC 61827 — Characteristics of inset and elevated AGL luminaires (environmental sealing reference). Always verify the current edition and your aerodrome's approved requirements.
Q7How often should a Gasket be inspected and maintained?
Typical maintenance tasks and intervals are: Compression Set Inspection (annual); UV & Ozone Degradation Check (annual); Chemical Resistance Check (annual); Seating & Installation Check (whenever disturbed). Your airport's approved maintenance programme takes precedence.
Q8How do I troubleshoot common Gasket faults?
Common symptoms covered are: Moisture Fogging or Condensation Inside the Fixture; Gasket Brittle, Cracked, or Crumbling; Gasket Swollen or Softened; Seal Fails Shortly After a Maintenance Visit. For example, for "Moisture Fogging or Condensation Inside the Fixture": Likely Cause: Gasket has taken a permanent compression set and lost its sealing force, or was twisted/pinched during a previous reassembly and never sealed correctly. Diagnostic Steps: Remove the cover and inspect the gasket for flattening, permanent deformation, or visible gaps in the seal line; check for twist marks or pinch points against the mating surface. Corrective Action: Replace the gasket with a new one of the correct material and size, seat it carefully and evenly around the full perimeter, and torque the cover fasteners to the specified sequence and value.
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