| 摘要 |
<p>A ventilation system comprises a duct 4 that defines an air passage and has an inlet; and at least one flap 5 to seal the duct 4 when the ventilation system 1 is quiescent, the system 1 preferably being associated with a motorized fan housed in the duct. The flap 5 has a first portion 11 and a second portion 8 about which it rotates about a pivot member 9, wherein the first portion 11 has a greater surface area than the surface area of the second portion 8 and the weighting of the second portion 8 is such that the flap 5 is biased to the closed position. Fig. 1</p> |
