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Handbook of Turbomachinery Second Edition Revised - Ventech!

Handbook of Turbomachinery Second Edition Revised - Ventech!

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elatively high unit costs. Frictional losses are relatively low with Roots<br />

blowers because the only rotating contact is between the synchronizing<br />

gears, which usually run in their own lubrication chamber. However,<br />

because <strong>of</strong> compression difficulties, the overall efficiency <strong>of</strong> Roots blowers<br />

can be below 50%. Low friction and a design that eliminates out-<strong>of</strong>-balance<br />

forces allow the Roots-type blower to run at speeds up to 10,000 rpm. Speed<br />

limitations result from rotor flexing that can cause rotor lobes to clash or<br />

due to excessive thrust loading can cause the rotors to operate out <strong>of</strong> phase<br />

or bearings to spin in their housings (Fig. 7).<br />

High noise level has been a long-time disadvantage <strong>of</strong> Roots-type<br />

superchargers, which produce a very distinctive noise, especially at low<br />

Figure 7 The Roots-type blower is a rather complex piece <strong>of</strong> machinery. The twin<br />

rotor lobes can be seen in the actual supercharger in the upper portion <strong>of</strong> the picture.<br />

(Courtesy B&M Automotive Products.)<br />

Copyright © 2003 Marcel Dekker, Inc.

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