时间：2011-03-11 23:11来源：蓝天飞行翻译 作者：admin 点击：次
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A lean fuel-air mixture burns more slowly than a rich mixture, and it can still be burning during the time of valve overlap (the time when both the intake and the exhaust valves are open). This causes a backfire. backfire (welding). A condition in which the flame burns back inside the tip of an oxy-gas torch. If a backfire occurs, the gases must be shut off at the regulator to stop the fire inside the torch. background noise (electronic equipment). Any noise heard or seen in a piece of electronic equipment when no signal is present. Background noise in a radio receiver is normally heard as a steady hiss. backhand welding. A method of welding in which the flame is directed back over the finished weld, rather than ahead of the weld. backing (meteorology). Shifting of the wind in a counterclockwise direction with respect to either space or time. Backing is the opposite of veering and is commonly used by meteorologists to refer to a cyclonic shift (counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere). backing plate (sheet metal repair). A reinforcing plate used when making a sheet metal repair. Backing plates are often called doublers. backlash. The play, or relative movement, between the teeth of mating gears caused by improper preload adjustment or worn teeth. backlash check (gear measurement). A check for the proper mesh between gears. This is done by measuring the amount of clearance between the teeth of the two gears. One of the gears is held rigid and the amount the other gear can move is measured to determine the amount of backlash. backplate (brake component). A floating plate on which the wheel cylinder and the brake shoes are attached on an energizing-type brake. back pressure (reciprocating engine). The pressure inside the exhaust system of a reciprocating engine that prevents complete scavenging of the burned gases from the cylinders. Back pressure is caused by mufflers and such power-recovery devices as turbochargers and power-recovery turbines (PRT). See turbocharger and PRT. backsaw (woodcutting saw). A fine-toothed hand saw which has a stiff spine along its upper edge. Backsaws are used to make straight or angled cuts across a board and are often used with a miter box to cut an accurate angle. backscatter (radar meteorology). Radar energy that has been reflected or scattered by a target. Backscatter is also called an echo. back-suction mixture control. A type of mixture control used in some float carburetors that regulates the fuel-air mixture ratio by varying the pressure of the air above the fuel in the float bowl. back taxi (air traffic control). A term used by air traffic controllers to taxi an aircraft on the runway opposite to the traffic flow. The aircraft may be instructed to back-taxi to the beginning of the runway or at some point before reaching the runway end for the purpose of departure or to exit the runway. backup ring. A flat leather or Teflon ring installed in the groove in which an O-ring or T-seal is placed. |
