| 摘要 |
<p>A powered, direct discharge ventilator comprises a base (B) having an extraction fan duct defined by a cylindrical wall portion (11) enclosing a fan impeller (not shown) of a fan (K) mounted on the base. A shallow windshield (D) shelters a non-return shutter (S) which closes the extraction fan duct when the fan is not operating. The shutter (S) is hinged on a pair of arms (H) to float up on the discharging airstream to take up the position shown chain-dotted in Fig. 1 when the fan is operated. When the fan is stopped, the shutter (S) closes gravitationally. To assist in holding the shutter (S) closed under high wind conditions, a wind deflector (W), carried by a bird-guard (G), directs the wind in a downwardly directed stream onto the top of the shutter (S). Where a much higher windshield is used, the wind deflector acts in a similar manner to prevent any reduction of pressure within the windshield due to the <<wind-over effect>> lifting the non-return shutter.</p> |
