Downloaded from https://www.everyspec.com FM 1-509 Air. Characteristics. Assuming a constant temperature, the volume of a confined gas changes in opposite order to changes in pressure. For example, if a given-volume of gas is reduced to half its initial size, its pressure doubles; if the volume doubles, the pressure is halved. This characteristic of gases is known as Boyle’s law and is expressed by the equation-- V x P = V 1 x P 1 where V = initial volume P = initial pressure V 1 = changed volume P 1 = changed pressure If the measurements of any three factors above are known, the fourth factor can be determined.
For example, assume that 30 cubic inches of gas (V) at a constant temperature and under 90 psi of pressure (P) is forced into a 15 cubic-inch space (V 1 ). To find the changed pressure (P 1 ), substitute in the equation as follows: Uses. When subjected to an applied force, a gas (such as air or nitrogen) acts in a manner similar to a spring: it yields but pushes back with as much force as is being applied to it. This characteristic of gases makes them useful in aircraft systems. In fact, some components are designed to use gas even though a spring would work. This is because gases weigh less than metal springs and are not subject to metal fatigue.
Air is the gas commonly used in hydraulic systems. It is used in accumulators, shock struts, emergency systems, and system reservoirs. In terms of compressibility, almost any gas could be used, but many are dangerous because they are flammable or explosive. Pure nitrogen is the only safe substitute authorized for atmospheric air in hydraulic systems. SAFETY DEVICES Aircraft vibration tends to loosen or change the adjustment of various parts such as nuts, turnbuckles, and screws. Therefore, parts that are used for disassembly or adjustment are safetied by some device.
The safetying devices commonly used on aircraft are cotter pins, check nuts, lock washers, safety pins, lock rings, and safety wire. An incorrectly installed safetying device or failure to install one where it is needed can cause a component to fail. See TM 55-1500-204-25/1 for detailed information on safetying devices. 1-10