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.
[Illustration: 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.