时间：2011-03-11 23:18来源：蓝天飞行翻译 作者：航空 点击：次
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Zerk fitting (grease fitting). The registered trade name for a type of fitting used to put grease into a bearing. A hole is drilled through the structure to the location where grease is needed, and a Zerk fitting is installed in this hole. The Zerk fitting has a ball-shaped top that is gripped by the nozzle of the grease gun when pressure is applied. Grease is pumped through the fitting into the bearing until it flows out between the surfaces of the bearing. When the grease gun is removed from the Zerk fitting, a check valve inside the fitting prevents grease leaking out, and prevents dirt getting into the bearing through the fitting. zero (mathematical quantity). A numerical quantity that has no value. Zero is used as a reference point on a number line from which values on both sides of zero are measured. zero (temperature). A reference used in the measurement of temperature. In the measurement of absolute temperatures using both degrees Kelvin and degrees Rankine, zero is the point at which all molecular movement stops. In the measure of temperature using the Celsius scale (the centigrade scale), zero is the temperature of melting ice. In the measure of temperature using the Fahrenheit scale, zero is the temperature of a mixture of ice and salt water. zero adjustment (electrical measuring instrument). The adjustment of the pointer of an electrical measuring instrument so that the needle rests over the zero mark on the dial when no current is flowing through the moving coil of the meter. zero beat (frequency adjustment). A method of determining the exact frequency of an alternating current. Vibrations caused by a variable-frequency alternating current are mixed with vibrations caused by the alternating current whose frequency is to be found. When the two vibrations mix, a third vibration is formed whose frequency is the difference between the frequencies of the first two vibrations. The variable frequency is changed until the third vibration disappears. At this point, the two frequencies are exactly the same. The beat has been reduced to zero. zero-center ammeter. An ammeter in a light aircraft electrical system located between the battery and the main bus. This ammeter shows the current flowing into or out of the battery. zero fuel weight (aircraft weight). The weight of an aircraft with all of the useful load except the fuel on board. |
