A number of ancillaries are available for fans and some of these are described in this Chapter. Whilst flexible connections, matching flanges and guards are obvious additions, the list is virtually endless and, indeed, seems to be growing by the day. There is also some competition between those manufacturers who provide at least some of these “appurtenances” and specialist suppliers for items such as dampers.
With the increasing importance of issues such as noise and vibration, the demand for attenuators and anti vibration mountings has increased. The problems of adequate maintenance have also become important leading to continuous monitoring of bearings and to automatic greasing systems, etc.
In HVACR, tunnel ventilation and grain drying applications, automation proceeds apace. Instruments are now being added to ensure that the fan is only activated when it can do useful work.
The moral is obvious — don’t just read this Chapter for information on ancillaries. You may well find the information for a particular instrument in Chapters 8, 14, 15 or even 21.
In addition to the special features detailed in Chapter 8, fans may also be furnished with ancillaries, which enable a working fan set to be self-sufficient. In American parlance, these ancillary pieces are known as “appurtenances”. Exactly what differentiates a special feature from an ancillary may be the subject of debate e. g. bolted-on upstream guide vanes on an axial flow fan are designed to provide contra-rotation to the airstream and thus increase pressure development. In like manner diffusers fitted to the discharge side of all types of fan convert high velocity pressures into useful static pressure.
There are, however, a number of bolted-on ancillaries for which there can be no doubt. Many of these such as:
• flexible connections
• matching flanges
• dampers (back draught and controllable)
• noise attenuators
Can be fitted to both the inlet and outlet and are shown in Figure
For centrifugal fans, but similar “extras” are also available for axial and mixed flow fans.
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