The adoption of hydraulic lifts, in the place of locks and inclines, has recently come prominently to the front. The first lift of this description[280] was erected on the Weaver Navigation in 1875, for the purpose of connecting that river with the Trent and Mersey Canal. In this case the difference of level between the canal and the river is rather over 50 feet. Two wrought-iron troughs are employed to raise and lower the barges. The troughs are 75 feet by 15½ feet, and have 5 feet depth of water. They rest on a central hydraulic ram, three feet in diameter, working in two hydraulic presses underground, which can be connected at pleasure, making the troughs counterbalance one another. One trough ascends as the other descends. Hydraulic power is only required when the descending trough reaches the water in the lift-pit, the motion of the troughs being effected by removing about six inches from the lower trough. This arrangement is very economical of time, inasmuch as a 100-ton barge can be transferred from the river to the canal, and another from the canal to the river, in eight minutes. Although the difference of level, as already stated, is 50 feet, only the final lift of 4½ feet requires the expenditure of hydraulic power.
La Louviére hydraulic lift, which was only completed during the summer of 1888, is the largest hydraulic canal lift in the world. It was constructed for the Belgian Government by the Société Cockerill, of Seraing, from the designs and under the superintendence of Messrs. Clark, Stanfield and Clark, of Westminster, the consulting engineers of the Government, and the patentees of the system. The difference between the levels of the upper and lower canals—that is, the height the boats are raised—is 50 feet 6¼ inches. The lift consists of two pontoons or troughs, each 141 feet long by 19 feet broad, with 8 feet draught of water, and are capable of holding the largest size of barge that navigates the Belgian broad-gauge canal system. Such barges are capable of taking 400 tons of coal or other cargo, so that the total weight of the trough, water, and barge is not much under 1000 tons. This immense weight is supported on the top of a single colossal hydraulic ram of 6 feet 6¾ inches diameter, and 63 feet 9½ inches long, working in a press of cast iron, hooped continuously for greater security with weldless steel coils. The working pressure in this press is about 470 lb. to the square inch. The time actually occupied in the operation of lifting or lowering is only two and a half minutes. ([See illustration at p. 141].)
It is probable that there is a greater liability to accidents, with lifts than with either locks or inclined planes. Where a dead weight of some hundreds of tons has to be moved bodily, it must, of course, be necessary to provide correspondingly strong machinery, and this is not to be done without considerable cost. Several accidents have, indeed, recently occurred in hydraulic presses for lifts. One of these occurred with a steel press which burst under a pressure of 70 atmospheres. Another happened with a riveted steel-plate press, which leaked and rent under pressure.
On the Brussels and Charleroi Canal it was recently proposed to apply an hydraulic lift, for which the Cockerill Company made a cylinder, in which tightness was obtained by the use of cast iron, and strength by the use of steel, the cylinder being cut with projecting rings, turned to receive steel hoops, which were bored to a slightly smaller diameter, put on hot, and allowed to contract. A cylinder 2·06 metres (6 feet 9 inches) in diameter and 2 metres (6 feet 7 inches) high, was subjected, by means of force-pumps, to an internal pressure of 131 atmospheres, or four times that which would be required in practice. The French engineers, following the Seraing system, formed their cylinders of a series of steel hoops fitting one into the other, and with the flanges of the two outside hoops drawn together by tie-rods, the inside being lined with brass 0·0025 metre thick, applied with the mallet, so that the water may not come into contact with the joints. A trial cylinder was tested up to 170 atmospheres without yielding. On the Brussels and Charleroi Canal, however, it was decided to substitute a tunnel for the intended lift, so that the Cockerill cylinders were not applied.
Inclines, or lifts, are said by some authorities to effect a great economy, both in time and water, as compared with flights of locks. Much, however, must depend upon local circumstances.
One problem that is likely to press for solution in the immediate future is that of constructing locks or lifts that will enable ship canals to be worked with facility and economy. The proposal of the late Mr. Eads to construct a ship railway across the Isthmus of Tehuantepec was intended to overcome the necessity of such a canal, and was, indeed, a form of lift, of the practicability of which, however, we still await a conclusive demonstration. There is, of course, a natural limit to the size of locks that it is possible to work. That limit, however, does not appear to have been reached in any locks hitherto constructed. The Eastham locks on the Manchester Ship Canal will be the largest hitherto made; but we have seen that locks, even 100 feet longer, have been proposed for the Nicaraguan Canal. Of course, by the application of steam power, canal locks may be made of larger dimensions, and there are some instances in which such power has been attended with much advantage.
In 1868, steam-power was applied to the locks of the Delaware and Raritan Canal, and is said to have increased their capacity for traffic, and therefore that of the canal, by 50 per cent. The engine has two cylinders, 6 inches diameter, 12 inches stroke, and works a 3-feet drum, actuating a 1-inch wire rope, which passes over rollers, along the face of the lock, and round sheaves above and below. To this rope the boats are attached and hauled in and out, two at a time. The engine also raises and lowers the valves, opens and shuts the gates, and in one case works a swing bridge. For large docks (e. g. 600 feet by 800 feet) it has been proposed[281] to admit and take off the water by channels the full width of the length of the lock, the water entering and leaving the lock by a number of small sluiceways, through the walls at right angles to the axis. This water should, if possible, be supplied, not from the reach above, but from separate reservoirs. There will thus be two waterways at right angles to reach each other, one longitudinal for the passage of vessels only, and one transverse, for the passage of water only. This avoids the expense of maintaining the paddles in the lock gates, and all the risks attending longitudinal currents. The canal should be widened above and below by floating pontoons, not by fixed walls. The height of the lift may be varied as required up to 30 feet; a lift of 33 feet has been worked for twenty-five years with ease and safety.
FOOTNOTES
CHAPTER XXIX
[272] These locks will be found described and illustrated in a previous chapter.
[273] Zendrini’s ‘Della Acque Correnti,’ c. 12.