Ventilating Shaft Tops
Never seen cowls like these before. Closer inspection revealed they were a hard bitumen type material not disimilar to Shires Lynx cisterns. Luckily on top there is a patent number and I unearthed the following patent info
1,129,953. Ventilating-shaft tops. VAL DE TRAVERS ASPHALTE Ltd. 24 April, 1967 [17 Feb., 1966], No. 6973/66. Heading F4J. [Also in Division E1] A ventilator permitting the escape of water vapour from beneath an impermeable asphalt roof membrane 10 comprises a bituminous circular base 2, having grooves 3, a bituminous trunk 5 fused with the asphalt membrane, and a bituminous cowl 7 stuck on top of the trunk 5. The bitumen used for the ventilator may include china clay, whiting or asbestos or glass fibres as fillers. The trunk 5 and base 2 are integrally moulded, whilst the upper part of trunk 5 may be moulded separately from the lower part. A venturi-passage 6 of the trunk 5 includes a one-way valve formed by a ball 11 seated by gravity upon a restriction 9. In another embodiment (Fig. 2, not shown), the interior of the trunk is of comparatively large diameter, and has no restriction.
Ventilating Shaft Tops
Never seen cowls like these before. Closer inspection revealed they were a hard bitumen type material not disimilar to Shires Lynx cisterns. Luckily on top there is a patent number and I unearthed the following patent info
1,129,953. Ventilating-shaft tops. VAL DE TRAVERS ASPHALTE Ltd. 24 April, 1967 [17 Feb., 1966], No. 6973/66. Heading F4J. [Also in Division E1] A ventilator permitting the escape of water vapour from beneath an impermeable asphalt roof membrane 10 comprises a bituminous circular base 2, having grooves 3, a bituminous trunk 5 fused with the asphalt membrane, and a bituminous cowl 7 stuck on top of the trunk 5. The bitumen used for the ventilator may include china clay, whiting or asbestos or glass fibres as fillers. The trunk 5 and base 2 are integrally moulded, whilst the upper part of trunk 5 may be moulded separately from the lower part. A venturi-passage 6 of the trunk 5 includes a one-way valve formed by a ball 11 seated by gravity upon a restriction 9. In another embodiment (Fig. 2, not shown), the interior of the trunk is of comparatively large diameter, and has no restriction.