The Bull engine is a simple cylinder, whose piston connects directly with the pump rod. If used at a shaft, the cylinder should be directly over the column of pipes; but if at a slope, the cylinder is set with the dip of the seam or the angle of the rods. In some cases this mode of connection is not convenient, and the ordinary connecting rods and "bob" are used; but, if possible, all indirect connection should be avoided. The steam is used direct to lift the rods, and the pressure on the piston must be equal to or greater than their weight, in order to raise them; and the rods must be equal to or greater than the weight of the column of water in the pipes, since the weight of the rods re turning forces up the water; that is, the engine simply lifts the rods, and the weight of the rods lifts the water.
There is another effective mode for pumping water from deep mines, and that is, the direct use of steam in both lifting and forcing water, by which the same column of pumps can be made to throw double the quantity of water now produced. There would be but slight difference in the construction of the pump, and no more liability to derangement.
There is not, generally, more economy in this double-acting mode than in the single plunger pump, as far as the operation is concerned ; the first cost may be reduced, but the chief benefit to be derived is in deep shafts where two columns of pumps cannot be used, and where a single column is not sufficient to drain the mine. In this case, the single column may be made to discharge a double quantity of water by the simple change of the working barrel. We have not seen this mode in use at our mines, but have fre quently witnessed its operation in equally trying positions, and can fully recommend it in all such cases as above described.
If a mine produces 500 gallons of water per minute, or even considerably less, it is had policy to trust its drainage to a single pump of 500 gallons capacity per minute. All mining machinery, no matter how perfect, is liable to accident from various causes, and a few days' delay is sufficient to drown the mine; when the pump is just capable of keeping the water down, any, accumulation or delay may overpower its capacity. It is not safe to trust the drainage of a deep and extensive mine to less than double the pumping capacity actually required to keep down the water. Nor is it safe, even with double the pumping capacity, to trust it all to a single engine or a single pump. It would be more economy to erect two moderate-sized pumps in each mine that is de signed to be extensive, than one very large pump. This, we think, almost any practical engineer or "sump-man" will endorse.
The breaking of clack-pieces, and the bursting of pipes, are of frequent occurrence where the column is of great perpendicular height, and our mechanics and engineers have a habit of stretching the lift, and frequently make one lift do when two lifts are almost indispensable. When we consider the pressure that lies on the valves and pipes even at the depth of 300 feet,—which is one-third more than can be recommended,—we can imagine the liability to derangement and fracture ; but the full extent of the pressure that occasionally happens can be fully realized only by those who have seen the bursting of clack-pieces the dimensions and strength of which, by calculation, would bear perhaps ten times the pressure of the column. In working heavy pumps, or,
in fact, any mine-pump, it is almost impossible to guard against the water-hammer," or the accumulation of air beneath the plunger ; and sometimes a vacuum is created between the plunger and the water by the strangulation of the valves, or the "wind bore." The consequence of this is the sudden and violent fall of the plunger, and Of the immense weight of the rods, with full force on the water. The force of such a blow cannot be estimated except by its effects.
But both these difficulties may be obviated by a little care and ingenuity. A float in the sump, with a wire and bell, will always give warning when the water becomes low, and a column of gas-pipe from the working barrel will always allow the escape of air, or obviate the danger from the "water-hammer." In addition to the danger from accidents, there is always a liability to a sudden in crease of water,—sometimes from subterranean fissures containing pent-up reservoirs, and sometimes from springs which may be cut by the advancing works; but more frequently from sudden floods or long-continued rains, and the "caving in" of old workings, which open channels for the admission of the torrents pouring from the mountain-sides under such circumstances.
It is, therefore, best, safest, and most economical, eventually, to have not only double pumping capacity, but two independent pumps each more than capable of draining the mine.
The plunger pump is the only really reliable one for deep mines and heavy pumps,— particularly where the acids of the water have an injurious effect on iron, which is generally the case in coal-mines, where the decomposition of the iron pyrites frequently renders the water so destructive to iron that even cast plungers cannot be successfully used in pumps. We have seen, in such cases, a bar of iron two inches wide and three eighths thick cut through by mine-water in two weeks. Copper, glass, and wood are resorted to in such cases ; but, generally, cast-iron plungers, if kept well greased and packed, are the most available.
In sinking mines, slopes, or shafts, where the water must be sucked from the bottom of the pit, and, consequently, is accompanied by air and gravel, the common lifting pump is the only reliable one, and we do not think a better can be designed for the purpose.
A great many new pumps have been invented of late years, and some of them are admirable for certain uses; but, though we have personally examined most of them, we do not find any that can take the place of the old Cornish lifting pump for sinking mines, or of the plunger pump as a permanent fixture. The donkey pump and engine combined is very available under certain circumstances, or where steam can be taken down into the mine without loss by condensation, and where heavy lifts do not occur ; but the presence of additional valves. and the necessity for frequent stoppages to change the clacks and pack the pistons, render these pumps unreliable generally for mining purposes.