| 摘要 |
PURPOSE:To timely disperse the sound generating energy so as to restrict the generation of whistles by alternately arranging cut-blades whose blade-circular arc is short on the main plate side and cut-blades whose blade-circular arc is short on the sub-plate side. CONSTITUTION:In a centrifugal impeller 20, plural blades 36, 39 are held between a main plate 21 and a sub-plate 22 of the same diameter. The back edge of the blade 36 is cut so that the blads-circular arc is short on the main plate 21 side, and the back edge 39 being cut so that the blade-circular arc is short on the sub-plate 22 side. And the out-blades 36, 39 are alternately arranged. As a result, a time-difference can be produced between the times at which the back edge situated on the main plate 21 side and the back edge situated on the sub-plate 22 side traverse a tongue 29 of the casing. Consequently, the pressure fluctuation occurs when the blades 36, 39 traverse the tongue 29 of the casing is timely dispersed, the sound generating energy is also dispersed, and the generation of whistles is restricted.
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