Constant flow ventilation duct - has rolling body moved by air pressure towards reduced section of duct

摘要

A ventilation system to ensure a constant flow of air through a conduit at all pressures, has a conduit (5) whose cross section varies over its length, and which contains a rolling member, e.g. a ball or sphere (6) which is caused to move up the sloping lower face as the pressure increases thus reducing the aperture through which the air can pass, and ensuring the required constant flow. To give the required change in cross-section, the upper face has a more sharply curved central region.