SURFACE EQUIPMENT. 35 



The new double-stage compressor, just erected west of Ribbles- 

 dale shaft (see PI. 18), is compound and condensing with steam- 

 cylinders of 24 inches and 40 inches artd air-cylinders of 22 inches and 

 34 inches diameter, respectively. It works with a 4-foot stroke, 

 developing 301 indicated horse-power in the steam, and 268*8 in the 

 air-cylinders, showing a loss of 10*7 percent. The steam pressure is 

 kept at 80 and the air pressure at 50 lbs. per square inch. The coal 

 consumption is 3*8 lbs. per indicated horsepower per hour. This 

 compressor drives 22 rock-drills (34-inch) and one donkey-pump, but 

 is not run at its full capacity, the steam being cut off at half stroke. 



At the Champion Reef Mine there are in all 5 compressors at 

 work. Of these one is of the Sandycroft pattern. It is a single-stage 

 compound and condensing engine with a 20-inch air-cylinder, and 

 steam-cylinders 18 and 32 inches, respectively. The other four are of 

 Walker Brothers' patent. Two of them are similar to the one just 

 described ; and the other two are double-stage, compound and con- 

 densing engines with steam-cylinders 24 and 40 inches, and air- 

 cylinders 34 and 20 inches, respectively, with a 4-foot stroke. The 

 air is received in 2 egg^ended air-receivers 30 feet long by 7 feet 

 diameter. 



At this mine an average of 55 drills are kept at work, besides 

 which there are several donkey-pumps and three air-hoists. The 

 air pressure is maintained at 55 lbs. per square inch. The average 

 monthly consumption of coal for the five compressors is 1,463 tons, 

 and the total average cost of running them is £2,009 P er month, 

 which is at the rate of £33 per rock-drill per month, due allowance 

 being made for pumps and air-hoists. 



MlLL-MOTORS. — The mill-motors in use on the field are chiefly 

 of Sandycroft manufacture. They are of the horizontal girder 

 type, and are mostly compound and condensing. The majority of 

 them have steam-cylinders of 16 and 30 inches diameter with 

 a 3-foot stroke. The slide valves are usually fitted with Prodi's 

 Patent cut-off gear. The fly-wheels are about 14 feet diameter with 

 2-foot belt face, the power being transmitted to the mill shafting by 



D] 



