350 COALFIELDS AND COLLIERIES OF AUSTRALIA. 



be installed. The blades of this fan are very numerous (Tig. 

 219), and their depth is very shallow in relation to the dia- 

 meter of the fan, while their axial measurement is very long. 

 The outer edges of the blades are curved forward in the direc- 

 tion of rotation, and the air passages between the blades are 

 open towards the inflowing air. The inlet and outlet open- 



Fig. 219. Sirocco Fan. 



ings are of approximately equal diameter to that of the fan 

 itself, and very much larger in proportion than that of other 

 centrifugal fans. The volume of air discharged is greater than 

 that of other centrifugal fans of equal diameter. The fric- 

 tional resistance to the passage of a given volume of air is 



