Shrouded radial blades

This useful design is represented diagrammatically in Figure 1.64 and can handle free flowing dust-laden air or gas. The im­pellers have the ability to deal with higher burdens than the backward inclined type. They are somewhat more efficient (up to 65% static) than the open paddle and also able to run at higher rotational speeds and thus develop higher pressures. The blades are inherently strong, as centrifugal forces have no

Figure 1.63 Deep vane forward curved fan — typical characteristic curves

Bending effect. They are also simple and in sizes up to 900 mm can be easily flanged for rivetting and spot welding.

Blades are largely self-cleaning and are easily cleaned. Such fans are suitable for moderate free-flowing granular dust bur­dens.

It should be noted that the power rises continually towards free air (zero pressure) and a reasonable margin is necessary over the absorbed power, unless the system pressure can be accu­rately assessed. As the impeller has a backplate, wear is con­centrated on this, but casing wear is correspondingly reduced compared with the open paddle.

Because of its characteristics, the shrouded radial impeller is widely used on gas streams having a significant dust burden, for example induced draught on rotary driers for the quarry and roadstone industries. Atypical characteristic curve is shown in Figure 1.65.

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