Porosity inspection device for an acoustical hose conducting air

摘要

The porosity of a flexible air duct consisting of outer (1) and inner (3) layers made from wound porous strips (1A, 3A) is controlled by having an intermediate layer made from non-porous film (2) wound between the inner and outer layers in non-overlapping spirals (4), leaving gaps (5) of a predetermined size which remain porous. The non-porous film can be self-adhesive, thermally adhesive or moulded directly onto the outer or inner layer.