MINING PUMPS.
There are certain well-known difficulties and contingencies in installing and operating mine pumps: 1, The location of the mine is usually remote from supplies and any renewals or repairs which may be needed, are liable to be attended with excessive costs and delays; 2, The nature of the water in the mines is so highly acidulous that corrosion takes place in an incredibly small space of time. The action of sulphuric (diluted) acid which is found sometimes as high as two parts out of a hundred begins at once and continues until the iron or steel is destroyed; 3, The dust, grit, mud, etc., becomes mixed with the oil used to lubricate the pump; these ingredients find their way into the stuffing-boxes and cut the plungers.
Hence, ample and unusual precautions are made to overcome the foregoing conditions. Extreme care has to be used in securing all movable parts of the machine and the connecting pipes. The plungers are generally outside packed and handholes are arranged to permit free access to the water valves.
Fig. 438.—See page [148].
When pumps used in mining service assume large proportions, they are almost invariably described as pumping engines; there is no real difference between the two except the proportions. The same combination of engine and pump in the smaller sizes used for boiler feeding, etc., are called steam pumps.
Note.—The cost of repairing a half-inch globe valve which “gave out” in a mine in Venezuela, South America, was represented in a $45. machine charge and a mule ride of 35 miles to the shop containing a foot lathe and the same distance back to the mines. The cost in a more favorable location would be less than a dollar.
The Cataract steam pump, Fig. [437], is largely used in mining operations. Many years service has proved its peculiar and curious merits. Large columns of water may be raised to great elevation or forced against heavy pressures without shock or jar of any kind and with safety to the machinery and connections; abrupt and violent action of the water is also avoided. The Cataract, it may be explained, is a regulator invented by Smeaton for single-acting steam engines. John Smeaton, the inventor, was an English civil engineer born in 1724 and died in 1792. The device derives its name from its similarity to the optical disease—a cataract—as it is a supplementary or sliding cylinder with its piston attached very curiously to the main valve stem of the engine.
This cylinder—called the Cataract cylinder—is filled with oil which flows back and forth through a port connecting its two ends. This port is controlled by a valve which increases and diminishes the flow of the oil through the port. By means of the Cataract, the movements of the main steam valve are automatically graduated and controlled, so the speed of the piston is reduced as it nears the end of its stroke, allowing the valves to seat themselves gently and quietly, and the moving column of water to come to a gradual and easy rest.