PUMPING-MACHINERY.
The drainage of deep mines is a question of equal importance with any other con sideration in mining matters. To deliver 100 or 1000 gallons of water per minute from a depth of 100 or 1000 feet requires not only powerful machinery, but reliable and durable fixtures. If we take 500 gallons per minute as the maximum production of our deep mines, and 500 feet as their maximum depth, we still find that the amount of water discharged per day, and the weight of the column to be lifted, are enormous. An im perial gallon weighs over 12 pounds, and a column to discharge 500 gallons per minute should be 20 inches in diameter ; the amount discharged in 24 hours would be 720,000 gallons, or 3200 tons, and the column to be lifted by the engine not less than 30 tons 50 feet high per minute. By geared motion, working the engine to its maximum speed, this may be done by 130 horse-power. But the great weight of the load necessitates massive machinery and numerous connections in order to reduce the speed to the slow movements of so large a pump : consequently, direct action is to be preferred to geared motion, by connecting the piston of the steam-cylinder with the pump-rod and making the stroke of cylinder and pump equal. To effect this, a cylinder should not be less than 50 inches in diameter, where steam of 40 pounds pressure per square inch is used, in order that a surplus of power may be provided. A cylinder of this size,—ten feet stroke, —at five strokes per minute, would require per minute about 680 cubic feet of dense steam of a common pressure of 40 pounds per square inch; and a common geared engine of 30-inch cylinder, working at 20 revolutions per minute, would require per minute 750 cubic feet of steam of the same density to do the same work. Thus, when slow motion is required to lift heavy weights, the more directly the steam can act the more economical will be the expenditure of power ; but, as noticed in connection with the hoisting of coal, where great speed is required the reverse is the best economy.
In the instance here given of a drainage of 500 gallons per minute, we exceed the general maximum drainage of mines in this country, but are below that of the deep mines of England. The size of the pump given, however, we consider the largest that should
be used, or the largest that can be used with economy at great depth. An unbroken column of five hundred feet in length is double the perpendicular height at which a pump can be properly worked, since the pressure per square inch on the valves and working parts should never exceed one hundred pounds per square inch. Two hundq,d feet is perhaps the most economical and effective height.
Water weighs 62.5 pounds to the cubic foot ; a column of water 34 inches in perpen dicular height is equal to the atmospheric pressure,-14.7 pounds per square inch.
The Cornish pumps are acknowledged the best or most available for mining purposes; and the Cornish miners, having the most practical experience, have also had the most inducement to direct their experience and ingenuity to the economy of drainage, since their mines are deep and extensive and their fuel is costly. Their pumping arrange ments are, therefore, the most perfect known. At the Consolidated Mines, which are 1560 feet deep, from 2600 to 3000 gallons of water are raised 1200 feet high per minute; 4000 horse-power is provided, and about half the power is constantly at work. The whole number of engines is nine. The average duty of the Cornish pumping-engines is about 50,000,000 pounds of water lifted one foot high by the consumption of one bushel, or 80 pounds, of coal; which is about equal to 800 tons, or 179,200 gallons, lifted 500 feet high by the consumption of one ton of coal. This is double the duty of our best Bull engines, and three times the production of our geared pumping-engines.
But, taking into account the simplicity of the "Bull engine," the reduction in first cost, and its permanent and reliable character, with the abundance and cheapness of our coal, we consider the high-pressure Bull engines superior to the condensing engines as pumping-machinery for our anthracite mines.