To elongate the life of a backflow preventing device by suppressing the flattering of vanes of the backflow preventing device for a ventilating installation.
The backflow preventing device 23 has the plurality of rocking vanes. A straightening device 22 is disposed on the inlet side of an air flow to the backflow preventing device, and the straightening device has a plurality of straightening vanes and a means for independently adjusting the openings of the straightening vanes. The backflow preventing device 23 and the straightening device 22 are provided in a common case body 16, where the openings of the plane vanes of the straightening device 22 are individually differentiated to suppress drift in a ventilating duct and adjust wind pressure on the plane vanes 15 of the backflow preventing device 23. Thus, the stability of the plane vanes of the backflow preventing device at their opening positions is improved, thereby the life of the backflow preventing device is elongated.
KAWABATA JUNICHI
ONCHI KINZO
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