| 摘要 |
PURPOSE:To restrain dispersed state of the winds and the creation of turbulence so as to reduce noise by disposing a variable electric resistance within an area from the approximately middle part of the internal bottom part of an outlet opening on a scroll casing up to an adjacent part to the side wall near the base end part of said casing. CONSTITUTION:The variable electric resistance 11 of a resistor 10 is disposed within an area from the approximately middle part of the internal bottom part of an outlet opening 5 up to the base end part of a scroll casing 2, that is, the adjacent part to the side wall near the side at which a sirocco fan 6 is placed. In operation, the variable electric resistance 11 is then exposed to intensive winds having a high velocity and cooled off efficiently to restrain the variation rate of the resistance value of the resistance 11 so that the revolutional speed of a motor (not illustrated) may be kept to a specified value and the air quantity of the specified value can then be obtained. In addition, the presence of the variable electric resistance 11 does not result in increase in the level of produced noise and the low-noise operation can be attained. Thus, the dispersed state of the winds and the creation of the turbulence are restrained and the low-noise operation can be attained without requiring any complicated construction.
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