Plug doors are a common part of many airplanes. When boarding an airplane, passengers will typically enter through a plug door. Airplanes may contain other types of doors. Cargo doors, for instance, feature a different design. Nonetheless, plug doors provide an entry point and an exit point for passengers.
What Is a Plug Door?
A plug door is a special type of self-sealing door that’s commonly found on airplanes. It leverages differential pressure to remain shut. As an airplane ascends, its plug doors will seal themselves.
How Plug Doors Work
Plug doors work by sealing themselves in response to the pressure difference. As the pressure on one side of a plug door changes from that of the other side’s pressure, the plug door will seal itself.
Airplanes, of course, have pressurized cabins. The air is less dense at high altitudes than at sea level. To create a safe and comfortable cabin environment, airplanes pressurize their cabins. This means the pressure inside of airplanes will be greater than the exterior pressure at high altitudes. With this differential pressure, plug doors will seal themselves.
Plug Doors vs Traditional Doors
There are different types of doors. Traditional doors require a locking mechanism to remain shut. Some of them have latches or bolts, for example. After closing a traditional door, a latch or bolt is engaged so that it won’t open. Plug doors don’t feature a latch, nor do they feature a bolt.
Plug doors feature a wedge-like design that allows them to seal themselves when the interior pressure is different than that of the exterior pressure. As long as there’s a difference in pressure, plug doors will remain sealed. They won’t be able to open when an airplane is flying at high altitudes and the cabin is pressurized. As a result, plug doors are a safety feature.
If a plug door — or any other type of accessible door — is opened during flight, it could create a safety hazard for passengers. Plug doors can only be opened once an airplane has descended and its cabin is no longer pressurized. As the cabin pressure decreases, the airplane’s plug doors will unseal themselves.
Other Applications for Plug Doors
In addition to airplanes, plug doors are commonly used on spacecraft. Several Apollo spacecraft, for instance, have featured plug doors. They used a similar self-sealing design as the plug doors found on airplanes. Spacraft typically feature hatch-shaped plug doors, though.
