Ventilation grille for underground tunnel - has series of freely pivoted flexible flaps and overlying powered openwork flaps for two way ventilation

摘要

The ventilation grille is used in a tunnel, e.g. in the underground system and provides two-way ventilation. It comprises a number of separate outer flaps (5), these being arranged in series and attached to freely moving pivots (6). These flaps move out against stops (10) when blowing air into the tunnel. Behind each of these flaps is another set of flaps (4), these latter being made from expanded metal and attached to pivots (8) which are connected to a power cylinder through linkages. When it is required to extract air from the tunnel, these open inwards to provide an unrestricted passage.