| 摘要 |
<p>The air extractor comprises lower (4) and upper (5) sections which face one another and are joined together by spacers (6) to provide a gap between them which acts as a Venturi tube in communication with an aperture in the lower section. The upper section of the extractor is generally circular in shape with a recessed centre and an outer diameter more or less the same as that of the lower section. The diameter of the central recess in the upper section of the extractor is more or less the same as that of the aperture in the lower section, or between 0.8 and 1.25 times the diameter of the aperture, and between 0.4 and 0.6 of the outer diameter of the upper section.</p> |
