| 摘要 |
A fan assembly, which includes a centrifugal-type fan wheel mounted for rotation in, e.g., a scroll-like fan casing or a tubular fan casing is provided with a retractable fan inlet funnel which may be selectively positioned relative to the fan wheel between an extended position and a retracted position. In the extended position, the inlet funnel axially overlaps the inlet side of the fan wheel with substantially all the inlet air being directed into the fan wheel. In the retracted position, the inlet funnel is spaced away from the fan wheel to permit a portion of the fan wheel outlet air to recirculate to the inlet side of the fan wheel. The inlet funnel has a converging/diverging venturi shape and is movably connected to a truncated conical base by a linkage assembly. The assembly includes a plurality of links each of which has one end pivoted to the base and the other end pivotally connected to a support ring which is connected to the inlet funnel by struts. Pivotal movement of the links, either by a torque member or a leadscrew/nut arrangement, causes the inlet funnel to change its position relative to the fan wheel and thereby vary the fan performance.
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