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See also:PISTON (through Fr. from Ital. pistone or pestone, a See also:great pestle, from See also:Late See also:Lat. pistare, to See also:pound, a frequentative See also:form of classical Lat. pinsere) , in the See also:steam See also:engine, a disk or See also:partition placed inside the See also:cylinder, from end to end of which it moves alternately under the pressure of the steam . By means of the " See also:piston-See also:rod " attached to it this forward and backward See also:motion is communicated to the machinery which the engine is employed to drive, and is in most cases converted into rotary motion by a " connecting-rod," one end of which is jointed to the " See also:cross-See also:head " carried at the end of the piston-rod, while the other turns the See also:crank on the crank-See also:shaft . The piston in See also:gas, oil and See also:air engines has a, similar See also:function, but in a See also:pump, instead of imparting motion, it has motion imparted to it by some See also:prime-mover . In every See also:case the piston must See also:fit the cylinder so accurately that as little as possible of the working fluid, whether it be steam, gas or See also:water, can See also:escape past it, packing of various forms being commonly placed See also:round its periphery in See also:order to secure this fit . In See also:music, the valves which in certain See also:wind See also:instruments, such as the See also:cornet, enable the player to increase the length of the air-See also:column and thus See also:lower the See also:note produced, are known as pistons . |
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