| 摘要 |
<p>The shutter (2) is mounted on a horizontal pivot (3) in the rectangular opening in the wall (1) of the building. The pivot (3) is above the mid point of the shutter height and the shutter (2) is provided with a counter balance weight (4). The shutter (2) is held in its vertical position by the catch (5) mounted on the pivot (6). If the pressure on the left hand side of the shutter rises above the pressure on the right hand side, the shutter rotates in anti-clockwise direction and overcomes the force exerted by the catch (5). The catch (5) rotates clockwise and allows the shutter (2) to swing through 90 deg. until it comes to rest on the stop (9). The pressure on both sides of the wall (1) is then equalised.</p> |
