| 摘要 |
A fan system or method of controlling a fan system comprises a displaceable fan shroud common to both a first (duty) fan 103 and a second (back-up) fan 102. The first and second fans are in-line. The displaceable shroud is pivotally moved to alter the flow characteristics of the fan system so that airflow from an outlet 108 of the system is switched between the first and second fan. The shroud is hinged 109 intermediately between the first and second fans, and in a first position provides an airflow guiding surface for airflow from the first fan and in a second position provides an airflow guiding surface for airflow from the second fan. The shroud may have a concave surface 107 and a convex surface on opposite sides. A pneumatic piston 110 may be used to drive the displaceable shroud. The shroud may be driven intermediate of two extreme positions enabling both fans to operate simultaneously. The fans may be centrifugal fans.
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