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impulse turbine[′im‚pəls ¦tər‚bən]
A turbine in which fluid is deflected without a pressure drop in the blade passages. A turbine is a power-producing machine fitted with shaft-mounted wheels. Turbine blades, attached to the wheels' periphery, are driven by the through-flow of water, steam, or gas. The rotary motion of the wheel is maintained by forces imparted to the blades by the impingement against them of high-speed fluid streams. Before the stream of fluid reaches the moving turbine blades, it is accelerated in stationary passages called nozzles. The nozzles are shaped to convert mechanical or thermal energy of the fluid into kinetic energy; that is, the nozzles increase the fluid's velocity while decreasing its pressure and temperature. Upon leaving the nozzles the high-speed fluid strikes the moving blades, and a force is imparted to the blades as the fluid is deflected by them. If the fluid's deflection in the blade passage is accompanied by a pressure drop and a relative velocity rise, the turbine is called a reaction turbine; if the fluid is deflected without a pressure drop in the blade passages, it is called an impulse turbine. See Nozzle, Reaction turbine