At ground level, the air pressure is a little over 14 pounds per square inch PSI. When an airplane reaches its typical cruising altitude — usually about 30, to 40, feet — the air pressure may be just 4 to 5 PSI. The low air pressure associated with high-altitude flights can restrict passengers from receiving an adequate amount of oxygen unless the cabin is pressurized.
Low air pressure means the air is less dense. Therefore, it contains less oxygen. Airplanes need pressurized cabins because it ensures passengers, as well as crew members, receive an adequate amount of oxygen in the air they breathe. The good news is that modern-day airplanes are designed with redundancy measures in case of pressurization failure. Passengers can place one of these oxygen masks over their face to obtain a sufficient amount of oxygen until the airplane descends and lands.
Hoses are commonly used in both automobiles and airplanes. Consisting of rubber tubes, they are We use cookies to improve your experience. By your continued use of this site you accept such use. Our team at AviationHunt is a group of aviation experts and enthusiasts. We aim to provide the best aircraft maintenance practices, technology, and aviation safety tips. Great article! Your email address will not be published. Save my name, email, and website in this browser for the next time I comment.
Skip to content. Cabin Pressurization System in modern aircraft The airplane operates at altitudes where the oxygen density is not sufficient to sustain life. It is composed principally of : 78 percent nitrogen, 21 percent oxygen, and 1 percent remaining various gases in smaller quantities.
Source of air for cabin pressurization The air conditioning packs force air into the airplane pressure vessel cabin. Control of Cabin Pressure Controlling cabin pressurization is accomplished by regulating the amount of air that flows out of the cabin.
Outflow Valve A cabin outflow valve opens, closes, or modulates to establish the amount of air pressure maintained in the cabin. Positive Pressure Relief Valve Pressurization safety valves are used to prevent the over-pressurization of the aircraft cabin. Negative Pressure Relief Valve The negative pressure relief valve prevents negative differential pressure vacuum pressure damage to the airplane structure.
Ventilation System Ventilation is achieved by controlling the rate at which the air enters the cabin and the rate at which it is allowed to leave.
Facebook Twitter. Great, this group is full of experts, experienced, enthusiastic personnel. Leave a Reply Cancel reply Your email address will not be published. The air packs compress the incoming air to heat it before sending it to another intercooler to dump the heat to the outside. The air then expands through an expansion turbine, which cools it the way blowing with your lips pursed results in a cool flow of air.
Now the air is ready to mix with air from the cabin in a mixer, or manifold , that adds the new air to the recirculating cabin air, which is moved by fans. To maintain a comfortable temperature for the passengers, automatic systems regulate the mixture of heat from the engines and cold from the air packs.
To maintain the pressure in the cabin equal to that at low altitude, even while the airplane is at 30, feet, the incoming air is held within the cabin by opening and closing an outflow valve , which releases the incoming air at a rate regulated by pressure sensors.
Think of a pressurized cabin as a balloon that has a leak but is being inflated continuously. On the ground, the airplane is unpressurized and the outflow valve is wide open. During preflight, the pilot sets the cruise altitude on a cabin pressure controller. As soon as the weight is off the main wheels at takeoff, the outflow valve begins to close and the cabin starts to pressurize. Your ears may pop, but the effect is mild because the climb rate is only feet per minute. When the airplane descends, the pilot sets the system controller to the altitude of the destination airport, and the process works in reverse.
The structural strength of the airplane determines how much differential pressure the cabin can tolerate—a typical figure is eight pounds per square inch—and the fuselages of new airplane designs are pressurized and depressurized many thousands of times during testing to ensure their integrity.
The higher the maximum differential pressure, the closer to sea level the system can maintain the cabin. Federal Aviation Regulations say that without pressurization, pilots begin to need oxygen when they fly above 12, feet for more than 30 minutes, and passengers have to use it continuously above 15, If the door blew off a jet at altitude, all the air in the cabin would depart very quickly and a momentary thick fog would envelope the cabin as the water vapor in the air condensed instantly.
Loose articles would fly around and foam rubber would burst as the tiny air bubbles within it expanded.
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