The economic advantages of balanced hoisting are so well known that wherever we ﬁnd a shaft or incline with two hoist compartments, we expect to ﬁnd that method in vogue as a matter of course. If, however, there is but one hoist compartment, we are apt to accept unbalanced hoisting as a necessary, if comparatively expensive, method of operation.
Any mine operator who has tried both ways of hoisting can quickly tell us how much of a saving in power, and in dollars and cents, balanced hoisting has meant to him.
Perhaps he originally operated his mine through a small shaft with only one hoist compartment. If, on the development of the mine, the tonnage warranted it, he probably went to the expense of remodeling his shaft to accommodate another hoist compartment in order to thus admit of hoisting in balance. On the other hand, suppose with the increased age of the mine, not only the available tonnage decreased till not even the one compartment was kept busy in hoisting, but the decreasing value of the ore necessitated the strictest economy to admit of a proﬁt margin.
Perhaps no other mining region in the world offers so many examples of where native ingenuity has been applied to effect hoisting in balance or partial balance as in the state of Colorado. An attempt has been made in the following to collect some typical examples not generally known in outside districts and present the essential data for sake of comparison.
Intermediate-Shaft Water-Tank Counterweight.
This device has already been described and illustrated in another article* but for convenience, the essential data are here repeated.
The intermediate shaft sunk on the Roosevelt drainage tunnel, about midway between the portal and the El Paso shaft, is 685 feet deep. It is 5 ft. X 10 ft. in the clear, having two compartments, a skipway 5 ft. X 5 ft. and a ladder and pipeway 5 ft. X 4½ ft.
The automatic dumping skip weighs, empty, 2,000 pounds, and full of rock weighs 5,600 pounds. The rock mucked in the El Paso heading of the tunnel will be hoisted to the surface in the skipway by the weight of the descending water-tank counterweight, already installed.
This tank, which runs in the ladderway compartment, is 12 feet long, 50 inches deep and 20 inches wide. Empty it weighs 2,250 pounds while full it weighs 7,986 pounds. The weight of the ½-inch cable is 600 pounds. The water tank is ﬁlled from a reservoir tank of equal capacity and when the skip is loaded with rock below, it is hoisted to the surface and automatically dumped.
This arrangement is planned to make a round trip of 1,370 feet in 5 minutes. Arrived at the tunnel level, the water is automatically discharged through a bottom valve into the drainage ditch. In starting to raise the 5,600 pounds of the loaded skip plus the 600 pounds of rope, the hoist is aided by the 7,986 pound weight of the water tank, while in lowering the skip, its 2,000 pounds weight is opposed by the 2,850 pounds combined weight of the empty tank and rope.
In hoisting the skip a 75-horsepower electric motor, geared to the double-drum hoist, furnishes just enough power to start the arrangement well under way, after which the power is shut off and the operation kept under control through the brakes of the hoist. In lowering the skip the peak load on the motor is but 850 pounds.
This apparatus, like that at the Findley Mine, was built and installed by the Pioneer Foundry and Machine Co., following out the ideas of Mr. A. E. Carlton.
* "Driving the Roosevelt Tunnel." See MINES AND MINERALS, April, 1909.