| 摘要 |
A flow control device is provided for use with a fan to prevent pressure excursions in a furnace or any other hardware equipment to which the fan is connected. The control device is connected in parallel relation with respect to the fan so that a recirculating flow path is formed between an outlet of the fan and an inlet thereof. This recirculating flow path controls the pressure differential produced by the fan. The control device includes duct work and a controlled element, preferably, a damper. In a furnace system, an induced draft fan is connected in series with a furnace and the controlled device is normally in a closed position in parallel with the induced draft fan. Upon the occurrence of one or more predetermined fault conditions, the controlled device modulates open to provide a circulating path through the induced draft fan and rapidly controls the pressure differential between the inlet and outlet of the fan. Since this pressure differential is maintained within a desirable range, the induced draft fan does not create too great a suction against the inner walls of the furnace.
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