THE SYDNEY HARBOUR COLLIERY. 



145 



small Walker's fan was installed at the bottom of the upcast 

 portion of the Birthday shaft, having 1 a capacity of 25,000 cubic 

 feet per minute, which was driven from the surface by an end- 

 less rope. The permanent fan is also one of Walker's (Fig-. 80), 

 24ft. in diameter, and 8ft. wide, provided with a Walker's 

 shutter, and guaranteed to produce 400,000 cubic feet of air 

 per minute, with 4iin. water gauge. The driving engine is a 

 compound horizontal, with 19in. and 25in. diameter cylinders, 



Fig. 79. 

 Wooden 

 Brattice. 



Fig. 80. Walker's Fan. 



and 4ft. stroke. It drives the fan with 11 cotton ropes, the 

 driving pulley being 18ft. in diameter, and the fan pulley 9ft. 

 in diameter. The engine is provided with Meyer's cut-off valve 

 for both high and low pressure cylinders, so that steam can 

 be regulated in either cylinder should the other have to be 

 cut out for any reason. This gear consists of two valves, the 

 main valve, A.B., and the expansion valve, E.F. (Fig. 81). 

 J 



