| 摘要 |
Co-axial pipes through a building roof expel burned gases through the inner and draw fresh air through the outer pipe. The pipes are in two parts (4, 5) that push together. A separate sleeve (15) has a cylindrical portion that lies within the overlap. It has an exterior flange (20). An interior flange (17) forms an abutment for the lower pipe (5). The pipe (5) has several openings (18) into which a snap fastener (19) locks. A similar fastener (22) engages an opening (21) in the upper pipe (4). The skirt (23) of the exterior flange (20) prevents ingress of rain.
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