What is a sealing system?
All the seals of a fixture, working together. Every path that water, dirt or insects could take into the lamp, optics and electronics is closed by a seal, and the fixture is only as dry as its weakest one.
Water that reaches the electronics, wiring or optics is one of the main causes of fixture failure. The sealing system closes every way in, so no single weak joint lets moisture through. Water inside a fixture can also break down insulation and show up as a falling insulation-resistance reading or an earth fault on the series circuit.
1It closes every path
A lens seal closes the front, gaskets close covers and the base joint, a cable-entry seal closes the point where the lead or connector enters, and in some products potting encases the electronics. Together they form one barrier.
2It has to last outdoors
The seals face heat, sunlight, rain, de-icing chemicals and vibration for years. A fixture also warms when lit and cools when off, so the air inside expands and contracts; a marginal seal can draw in damp air each cycle, which is why some products add a pressure-equalization vent. When one fails, moisture gets in, fogs the optics, corrodes terminals, damages insulation and shortens the life of the lamp, LED or driver.
3Find the path, fix the seal
Look for fogging or water inside the lens, water marks, corroded terminals, hardened or cracked seals and displaced parts. Find where the water got in, replace the faulty seal with the correct part, and refit and tighten as the manufacturer specifies. Seals and O-rings are normally replaced whenever the fixture is opened, not reused. Opening a fixture on a series circuit is maintenance work: isolate and prove the circuit dead first (see Safe Maintenance Sequence).
| Element | Detail |
|---|---|
| Sealing system | All the seals of a fixture working together |
| Seal points | Lens, covers, base joint, cable entry and connectors |
| Parts | O-rings, gaskets, cable glands or boots, and potting |
| Purpose | Keep out water, dirt, insects and chemicals |
| Failure result | Fogging, corrosion, insulation breakdown, early failure |
| Check | Seal condition at every joint, water or fogging inside, corrosion |
| When opened | Fit new seals and refit to the manufacturer's torque and instructions |
Frequently Asked Questions
Q1What is the sealing system of an airfield light?
All the seals of a fixture working together: the lens seal, gaskets at covers and the base, the cable-entry seal, connector seals and, in some products, potting around the electronics.
Q2How is the sealing system different from a gasket?
A gasket is one part of the system, a single seal between two faces. The sealing system is the whole set of seals along every possible path water or dirt could take into the fixture.
Q3What are the signs of a failing seal?
Fogging or water drops inside the lens, water marks, corroded terminals, a lamp or LED that fails early, and damaged or hardened seals. Find the leak path, replace the faulty seal with the correct part, and refit it as specified.
Q4Why can water get in even when the seals look intact?
A fixture heats when lit and cools when off, so the air inside expands and contracts. A worn or poorly seated seal can draw in damp air on each cool-down, and the moisture condenses inside. Hardened, cracked or wrongly refitted seals are the usual cause, so check every joint and replace the seal, not just dry the fixture.
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