194 



COALFIELDS AND COLLIERIES OF AUSTRALIA. 



The Reavell compressor is provided to supply air for work- 

 ing Little Hardy Coal Cutters, and being located in the mine 

 near the pneumatic drills, a great length of piping is saved. 

 These cutters are of the rock drill type, but are specially fitted 

 for coal mining work, and can be used for holing and shearing 

 in hard coal headings. The internal construction of the 

 machine will be seen from Fig. 120 to be a reciprocating air 



Fig. 121, Little Hardy fixed for Undercutting. 



drill, the chief feature of which is the valve, which is thrown 

 over at the maximum attainable speed by live air at full pres- 

 sure, which acts on the whole surface of one end of the valve 

 piston, while the opposite end is open to complete exhaust. 

 AVith a pressure of 451b., 450 to 500 blows per minute are 

 struck, while with 601b. pressure from 650 to 700 blows per 

 minute are obtained. The valve is circular in cross section, 



