Cap for outdoor end of ventilation pipe - consist of pair of unequal flat cones joined base to base and fitted across pipe

摘要

The cap which will neither build up a back pressure in the pipe, nor let the rain in, is formed of two unequal cones (2, 3), placed base to base (with the wider one on the outside). The cones are pref. circular or rectangular, and the pref. material is hard foam or fibre-reinforced plastic. The cones may be joined to each other by adhesive (4) or by clamping the edges (6).