What is a pressure-equalization vent?
A small membrane vent that lets a sealed fixture breathe as it warms and cools, while keeping water out.
A pressure-equalization vent is a small opening, usually closed by a membrane, in the wall of a sealed fixture. It lets air pass in and out so the pressure inside matches the pressure outside, while it blocks water and dust.
1Sealed air still changes pressure
The air inside a sealed fixture expands as it warms and shrinks as it cools, for instance when the lamp is switched on and off, or when rain cools a hot housing. Without a way to equalize, the pressure difference strains the seals and can draw moist air in past them.
2The membrane lets air through, not water
The membrane passes the air but resists liquid water and dust. It lets the fixture breathe without opening a path for moisture to reach the optical chamber. Many fixtures have no vent and rely on their seals and gaskets alone, so not every fixture has one.
3Keep it clear, intact and sealed
The usual faults are blockage by dirt, paint or ice, a damaged membrane, and a loose or missing vent. Check it only as the manufacturer allows, never pierce or poke the membrane, and replace it only with the type specified.
| Part | What it does | Main risk |
|---|---|---|
| Membrane | Passes air, resists water and dust | A tear opens a path for water |
| Opening | Lets pressure equalize | Dirt, paint or ice can block it |
| Vent seal | Seals the vent into the housing | A loose vent leaks |
| Position | Keeps the vent clear of water | Standing water can overcome it |
Frequently Asked Questions
Q1What is a pressure-equalization vent in an airfield light fixture?
It is a small vent, usually fitted with a membrane, in the wall of a sealed fixture. The membrane lets air pass in and out so the pressure inside matches the pressure outside, while it blocks water and dust.
Q2Why does a sealed fixture need to equalize pressure?
The air inside a sealed fixture expands as it warms and shrinks as it cools, for example when the lamp or LED is switched on and off or when rain cools a hot fixture. Without a way out, the pressure difference stresses the seals and can draw moist air in past them.
Q3Do all airfield light fixtures have a vent?
No. Many fixtures are sealed with no vent and rely on their seals and gaskets alone. A vent is a design choice made by the manufacturer, so check the product design before assuming one is fitted.
Q4What happens when a vent blocks, tears or leaks?
A blocked vent stops the pressure from equalizing, so the seals stay under strain. A torn or damaged membrane, or a loose or missing vent, opens a path for water and dust into the optical chamber, where it can spoil the reflector, lens or electronics.
Q5How should a vent be checked or replaced?
Only as the manufacturer's instructions allow. Look for dirt, paint, ice or damage over the vent, check that it is fitted and sealed, and do not poke or pierce the membrane. Replace a damaged vent only with the type the manufacturer specifies, and do not open a sealed optical chamber outside a controlled procedure.
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