Page:Encyclopædia Britannica, Ninth Edition, v. 16.djvu/476

Rh 458 MINING [DRAINAGE. 215 yards. The length and depth of this adit are not remarkable; but the great quantity of water discharged is a point of considerable interest and importance. It is estimated that this adit is now discharging 15 million gallons or 66,000 tons of water in twenty- four hours, although the outflow is purely natural, for no mines are pumping water into. it. It is now easy to understand that the Rhosesmor mine, though provided with powerful pumping machinery, was unable to cope with the springs it encountered. In the United States the famous Sutro tunnel is an adit of which the main branch, 4 miles in length, reaches the great Comstock lode in Nevada at a depth of 1700 feet. The total cost of this tunnel, which was completed in nine years, is estimated to have been $7,000,000. The quantity of water running out daily in 1879 was 12,000 tons, at a temperature of 123 Fahr. at the mouth of the tunnel. All this water must otherwise have been pumped to the surface at a cost estimated at $3000 a day. The obstacles to progress were very great : not only was the heat extreme, but swelling ground was encountered which snapped the strongest timber. Thanks, however, to the untiring energy of Mr Adolph Sutro, the difficulties were at last successfully overcome, and this great work will long remain as a monument to his foresight, skill, and patient pertinacity. The Atlantic-Pacific tunnel, 1 which was commenced in 1880, will pierce the heart of the Rocky Mountains under Grey s Peak, Colorado. It is being driven from both sides of the watershed, and will have a total length of 4f miles from end to end. Siphons. Siphons have been used for unwatering workings in special cases ; but of course they will not act unless the barrier over which the water is raised is very decidedly less than 33 feet. Winding When workings cannot be drained by tunnels or siphons machin- it is necessary to raise the water mechanically, either to ery- the surface or at all events to an adit through which it can flow away naturally. If the amount of water is not too considerable, it is often convenient to use the winding machinery and draw up the water in special buckets (water- barrels) or tanks. The bucket may be tilted over on reach ing the surface, or it may be emptied by a valve at the bottom. This means of raising water is often adopted while sinking shafts, when it may be desirable to wait till the whole or a portion of the shaft is completed before putting in the final pumping machinery. Pumps. The varieties of pumps used in mines are numerous. In small sinkings hand-pumps, either direct-acting or rotary, may be applied ; steam-jet pumps on the principle of the Girfard injectors are also used ; and pulsometers, though requiring a large expenditure of steam, have the advantages of being quickly fixed, of occupying little space, and of working with sandy or muddy water. They are capable, therefore, of rendering great services in special cases. When we come to the definitive machinery erected in large mines of considerable depth, we find that the pre vailing types of pumps are few. They may be classified as follows : (A) lifting and force pumps worked by rods in the shaft actuated by wind, water, or steam power ; (B) force-pumps at the bottom of the shaft worked by steam, compressed air, or hydraulic pressure. A. In describing the first method we have to consider the motive power, the rods, and the actual pumps themselves. Windmills have the disadvantage, which is often fatal, that the power is not constant. By erecting an auxiliary steam-engine, which can be set to work if wind fails, this evil is overcome ; and at the Mona mines in Anglesea a windmill pumps up water from a depth of 80 fathoms at the rate of upwards of 90 gallons per minute. As the site of the mine is breezy, there is wind enough to work the mill about one-half of the time. Water-power was for a long period the principal agent employed in draining mines, and it is still of the greatest utility in many districts, reservoirs being constructed to collect and store the rainfall. Some idea of the scale upon which these works are conducted will be gathered from the following figures relating to the Harz mines. In 1868 there were &quot; sixty-seven reservoirs covering an area of 604 acres, and having a storage capacity of 336,000,000 cubic feet.&quot; 8 The total length of the various leats, 1 Mining and Scientific Press, San Francisco, 1882, vol. xlv. p. 241. 2 &quot;Notes on the new Deep Adit in the Upper Harz Mines,&quot; by H. Bauerman, Report of the Miners Association of Cornwall and Devon shire, 1868, p. 21. races, and other water-courses, including the six principal adits, is about 170 statute miles. The net power extracted is reckoned at 1870 horse-power, but less than one-fourth of this is used for pumping. Water-power is applied to pumping machinery by water-wheels, turbines, and rotary or non-rotary water-pressure engines. Except ing the case of the latter, the rotary motion has to be converted into a reciprocating motion by a crank ; and furthermore with turbines the speed must be reduced very considerably by intermediate gearing. Overshot wheels are the commonest prime movers when pumps are worked by water-power ; water-wheels are frequently constructed 40 or 50 feet in diameter, and at the Great Laxey mine, in the Isle of Man, one of the wheels is no less than 72 feet 6 inches in diameter and 6 feet in the breast. The power is conveyed from the water- wheel by a connecting rod to a bell-crank (bob) placed over the shaft ; and when, owing to the contour of the ground, the wheel has to be placed at a distance, it is connected to the bobby the so-called flat rods, made of wood, bars of iron, or wire-rope, travelling backwards and forwards, and supported by pulleys or oscillating upright beams. Water-pressure engines have the advantage of being able at once to utilize any amount of fall, and those which are direct-acting can be applied immediately to the main rod of the pumps. Steam, however, is the power used par excellence in draining mines ; indeed the first applications of steam-power were made for this purpose, and Watt s great inventions owed their birth to the necessities of mines which could no longer be drained by the water- power at their command. The principal type of engine is that known as the Cornish engine, Cornish which is a single-acting condensing beam engine working ex- engine, pansively. Its mode of action may be briefly described as follows. The steam is let in at the top of the cylinder and presses down the piston, which is connected with one end of a large beam, whilst the main rod of the pumps is attached to the other. When the piston has completed its course the equilibrium valve is opened by a cataract, and, the pressure on both sides of the piston being now equal, the weight of the pump rods, or rather the excess of their weight over that of the counterbalances, causes them to drop and force up the water from the mine by means of the plungers, which will be described immediately. Double-acting rotary engines working the pumps by cranks may also be met with. The rod in the shaft, known as the main rod or ^ear rod, is usually made of strong balks of timber butted together and con nected by strapping plates fastened by bolts. It serves to work either lifting-pumps or force-pumps, or both. Fig. 87. Fig. 88. The lifting-pump, or drawing lift (fig. 87), 3 consists of the wind- bore, the clack-piece, the clack-seat piece, the working barrel 3 Michell and Letcher on &quot;Cornish Mine Drainage,&quot; Forty-Third Annual Report of the Royal Cornwall Polytechnic Society, p. 211.