| 主权项 |
1. Apparatus for allowing ventilation as usual through a ventilation shaft to an underground ventilation duct fluidly communicating through the ventilation shaft to an atmospheric opening of the shaft and on threat of flooding operable to prevent downward flow of surface water into the underground ventilation duct, comprising:
a support for arrangement in said shaft defining a passage between top and bottom openings of the support for fluid communication of said ventilation duct up through said support to said atmospheric opening, one or more stops within and connected to said support proximate said bottom opening and not obstructing said passage, one or more panels mounted in said support for rotation of the panels from or to an upright home position not obstructing said passage, in gravitational rotation falling from said upright home position to a lower passage closing position where further rotation is prevented by said one or more stops, said one or more panels having a profile that closes said passage when said panels gravitationally rotate to said passage closing position, and a panel holder having one or more moveable members holding the one of more panels in said upright home position and having a handle operable to move said one or more moveable members above said one or more panels to release the panels and allow the panels to gravitationally rotate downwardly to said passage closing position. |
