Aircraft Pressurization System
Airplanes, which do not have pressurization and air conditioning systems, are usually limited to the lower altitudes. They need to stay below 8,000 feet. A cabin pressurization system accomplishes several functions in providing passengers comfort and safety. It maintains a cabin pressure altitude of approximately 8,000 feet at the maximum designed cruising altitude of the airplane, and prevents rapid changes of cabin altitude, which may be dangerous to the passengers and crew. In addition, the pressurization system permits a reasonably fast exchange of air from inside to outside the cabin. This is necessary to eliminate odors and to remove stale air. Pressurization of the airplane cabin is now the accepted method of protecting persons against the effects of hypoxia. Within a pressurized cabin, people can be transported comfortably and safely for long periods of time, particularly if the cabin altitude is maintained at 8,000 feet or below, where the use of oxygen equipment is not required. In this typical pressurization system, the cabin, flight compartment, and baggage compartments are incorporated into a sealed unit, which is capable of containing air under a pressure higher than outside atmospheric pressure. Pressurized air is pumped into this sealed fuselage by cabin superchargers, which deliver a relatively constant volume of air at all altitudes up to a designed maximum. Air is released from the fuselage by a device called an outflow valve. Since the superchargers provide a constant inflow of air to the pressurized area, the outflow valve, by regulating the air exit, is the major controlling element in the pressurization system. It is necessary to become familiar with some terms and definitions to understand the operating principles of pressurization and air conditioning systems. These vocabulary terms are essential to know: 1. Ambient pressure. The pressure in the area immediately surrounding the airplane. ...
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