Ventilating system for cesspit - has automatic electromagnetically operated control to close natural ventilation when forced ventilation fan starts

摘要

The cesspit has one duct rising to the roof of the building for natural ventilation and a second duct with a motorised fan for forced ventilation. The natural ventilation duct terminates above roof level in a casing (5) with grilles (6) in its sides. Each grille has pivoting blades (8) which are linked and operated together. The operating arm (12) is pulled to open the grille by a spring (13). When the fan of the forced ventilation duct starts an electromagnet (9) is energised. The armature of the magnet pulls a cable (10) attached to the operating arm (12) to pull the arm against the spring (13) and close the grille.