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How Aircraft Cabin Pressurization Works

At the altitude range that most aircraft operate in, air pressure and oxygen density is often at a level that is unsafe for humans due to the risks of hypoxia. While some aircraft remedy this situation with portable oxygen systems for crew members and pilots, such methods are less optimal for larger airliners with many passengers. In those instances, the passenger aircraft utilizes pressurization, that being when cabin pressure is controlled to provide passengers with a safer environment that is closer to sea level conditions. As a reliable method that has long kept passengers safe and comfortable during flight, understanding the aircraft pressurization system can be useful for any interested individual or aircraft engineer.

In general, the higher one goes in elevation, the less air and oxygen will be taken into the lungs. This is because of how our lungs function, as they require inside air pressure to be less than that of the outside air so that they may inflate. While flying at a lower altitude can prevent these issues, such heights are often unsafe due to the possible presence of poor weather, mountains, and other obstructions as well as the fact that many engines are inefficient and slower when flying low. In a pressurized cabin, the interior is sealed to a degree to prevent the uncontrolled escape of air while pressurized air is pumped into the cabin with the pressurization system.

While the fuselage is sealed to mitigate the escape of air, there are outflow valves and openings to ensure that old air may be removed from the system for the means of recycling oxygen. The outflow valve is typically placed near the tail of the aircraft, and there may be one or two valves depending on the size of the model. The control of the outflow valve is automatic as it is managed by the cabin pressurization unit. Generally, the valve will close itself off when pressure needs to be maintained or increased, and it can slowly open as pressure is to be released. As such, maintaining a base pressurization from lift-off to landing can be achieved.

To ensure that passengers are always supplied with sufficient fresh air for breathing, the air within the aircraft is fully replaced every few minutes which can surpass the cleanliness of even homes or office buildings. To further clean air of any potential bacteria, viruses, or contaminants, medical grade filters are implemented throughout the oxygen system. Due to the rate of air replacement, the use of outflow valves, and the general design of the aircraft pressurization system, the pressure within the cabin tends to remain at a value reminiscent of altitudes between 6,000 and 8,000 feet. While maintaining a pressure value at sea-level would be the most desirable, such pressure differences between the cabin and the surrounding atmosphere could quickly lead to damage if the fuselage is not strong enough. To protect the cabin from the hazardous effects of pressurization, positive pressure relief valves and negative relief valves serve to automatically vent and bring in pressure to ensure safety as the aircraft adjusts its altitude.

The pressurized air that is provided to the cabin through the duct assembly pressurization system can come from a few sources depending on the aircraft. For many older piston powered aircraft, electric compressors served to pump in air under pressure for the cabin. While these systems were sufficient for pressurization needs, they were quite heavy. Despite this, new aircraft such as the Boeing 787 Dreamliner have brought back the electric compressor with advancements to its efficiency. The use of turbocompressors is another method that has served many early jet engines, and such systems were driven with bleed air in order to pump in fresh air into the cabin. For most modern airliners, engine bleed air serves as the common method for establishing pressurization, and such air is routed from the compressor of the engine and cooled before being directed to the cabin.

With the cabin pressurization unit and pressurization system, passenger aircraft can ensure a safe and comfortable environment with fresh air for all individuals on board. At NSN Gamut, we serve as a leading distributor of all types of aviation tools and parts required for aircraft maintenance, and we can provide competitive pricing on decal system pressurization products, cabin pressurization unit parts, valve components, and much more. If you find particular items from our catalogs that you wish to procure, we invite you to begin with a quote for your comparisons which you can receive in just 15 minutes or less upon the submission of an Instant RFQ form as provided on our website. Get started today and see how NSN Gamut is revolutionizing the part procurement process for our customers.


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