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Scientific American Supplement, No. 648, June 2, 1888试读：
THE ONE HUNDRED AND TWENTY TON SHEARS OF THE PORT OF MARSEILLES.
For a quarter of a century maritime nations have been continuously engaged in improving the mechanical appliances of their large ports. The use of tracks to bring goods to be placed on vessels as near as possible to the shipping point, the substitution of oblique moles for perpendicular ones in large docks, the creation of a hydraulic method of loading and unloading through movable cranes (which will perhaps in a near future cede to an electrical one), constitute the means most used for expediting transshipments and reducing the expense of them to a minimum. But, at the same time that the facilities for all kinds for handling packages have been increased, it has also become necessary to greatly increase the power of the machines applied to them. The construction of large packets now requires the putting in place of boilers of great weight, and the adoption of the huge pieces that compose the artillery of ironclads necessitates the use of force that has been unknown up to recent times.Fig. 1.—DIAGRAM OF SHEARS.Fig. 2.—ONE HUNDRED AND TWENTY TON SHEARS OF THE PORT OF MARSEILLES.
At present, then, we could no longer be content with manual power, acting upon windlasses or capstans, for lifting and shifting. It has become necessary to apply steam or hydraulic motors to these operations. Of these, the latter are the most used, on account of their easy operation and their submitting to the greatest stresses with a very satisfactory proportionality of the expenditure of motive power. One of the most remarkable of such apparatus is the one that the Compagnie de Fives-Lille has recently set up on one of the moles of the national dock at Marseilles, for the service of the chamber of commerce, and this merits a description so much the more in that it is an important improvement upon the analogous apparatus now in use in other ports.
According to the conditions of the programme, powers of 25, 75, and 120 tons had to be obtained at will, with a proportional output of water, and the load had to be lifted 22 ft. above the quay and carried horizontally from 28 ft. beyond the edge to 16 ft. in the rear, so that the load might be taken from a ship and deposited upon a wagon, and vice versa. The shears, then, had to be capable of performing two operations, viz., of lifting the load and of carrying it horizontally. To facilitate the description, we shall first make known the arrangements that assure the second operation.
The apparatus is of the type known as oscillating tripod. The tripod consists of two lateral iron plate uprights, A A (Fig. 1), resting upon the wharf wall, and of a beam, B, jointed to them above and connected below with the head of the piston of a hydraulic press. This latter rests upon an iron plate frame, solidly bolted to masonry. The piston pulls the beam, B, toward it when it descends, and carries along in the same motion the shears, A, as well as the load suspended from their point of junction, and the load is thus carried to a distance of 16 ft. from the edge of the wharf in order to be placed upon a wagon. Conversely, if the piston rises, it pushes before it the entire framework, as well as the lifting apparatus, the hook of which travels 28 ft. beyond the edge of the wharf.
The lifting apparatus consists likewise of a hydraulic press suspended from the summit of the tripod; but, in order to prevent the joints of the cylinder from working under the action of the load, which would tend to open them and cause leakages, it is not suspended from the very axis of the junction of the shears. The cylinder rests directly upon a huge stirrup 45 ft. in length, the arms alone of which are affixed to the axis, through a Cardan joint. Under such circumstances, the stress of the load carried by the piston rod is exerted solely upon the branches of the stirrup, and the sides of the cylinder work only under the pressure of the motive water. The latter is introduced at the base of the press, through a valve that a special workman, standing upon a platform supported by the stirrup, maneuvers at will.
It will be seen that the general principle applied for utilizing the motive power is that of direct action. It has already been employed in a few analogous apparatus constructed by Sir William Armstrong, especially those of the arsenal of Spezia and of the Elswick cannon foundry, but solely for the lifting press. This is the first time that use has been made of it to effect the oscillating motion corresponding to the horizontal shifting of the load. This was formerly done through the intermedium of a mechanism that, aside from its complication and higher cost, presented the inconvenience of absorbing a large quantity of force in friction; besides, the direct action permits of performing the maneuvers much more quickly by the use of the water in reserve contained in the accumulators.
Another important improvement, likewise due to the Compagnie Fives-Lille, consists in the addition of safety clicks, which engage with racks parallel with the piston rod of each of the presses and movable with it. The clicks, on the contrary, are jointed to axes fixed on the bottom of the cylinders. This arrangement presents the following advantages: If a leakage occurs in the joints or feed pipe of the hoisting press, the descent of the load can be stopped instantaneously, thus preventing the grave damage that would be done to ships and even to the shears themselves by the descent of a 120 ton load, however slow it might be. As regards the oscillating press, this arrangement permits of fixing the base of the connecting beam at any point whatever of its travel, when it is desired to dismount the piston. Further, it permits of maintaining the shears in an invariable position in case of sudden damages to the piping.Fig. 3.—AUTOMATIC MULTIPLIER.
In order to produce the three powers of 25, 75, and 120 tons required by the programme, and at the same time expend in each case a corresponding quantity of water under pressure, it is of course necessary to cause the pressure of the motive water to vary in the same proportion as the stress to be extended. This result is reached by calculating the diameter of the two cylinders in such a way as to obtain the mean power of 75 tons, in making the water of the general conduit act directly under the normal pressure of 50 atmospheres. For the powers of 25 and 120 tons, use is made of an automatic multiplier, that consists of two cylinders arranged end to end, in which move pistons, A and B (Fig. 3), of different diameters. When it is a question of lifting 120 tons, the water at 50 atmospheres actuates the piston, A, and the other forces into the lifting cylinder motive water under a much greater pressure. If the load to be lifted is but 25 tons, the water at 50 atmospheres actuates the piston, B, and A forces the water into the same cylinder at a much lower pressure. The same operations are effected in the other cylinder when the extreme loads of 25 and 120 tons are moved.
The shears are likewise provided with a hydraulic cylinder, E (Fig. 1), placed on the back of the beam, B, and serving, through a cable, to bring the piston of the large cylinder to the end of its upward stroke, and for certain accessory work.
Finally, the apparatus as a whole is completed by an accumulator containing in reserve a large part of the water necessary for each operation.
The apparatus is capable of lifting a maximum load of 120 tons from 22 feet beneath the wharf to 22 feet above, and of moving it from 28 feet beyond the edge to 16 feet back of it, say a total of 44 feet. The cylinders of the lifting and oscillating presses are 1¾ feet in diameter and 4 inches in thickness. The stroke of the second is 22½ feet. The length of the uprights is 110½ feet and that of the connecting beam is 109 feet. The apparatus has been tested under satisfactory conditions with a load of 140 tons.—La Nature.
THE DISTRIBUTION OF HYDRAULIC POWER IN LONDON.
At a recent meeting of the Institution of Civil Engineers, a paper on the above subject was read by Mr. Edward Bayzand Ellington, M. Inst. C. E. The author observed that water power was no new force, but that, as formerly understood, it was limited in its application to systems of mechanism suitable for the low pressures found in nature. The effects obtained by the use of high pressure were so different in degree from all previous experience, that a new name was needed, and had been found in the term "hydraulic power." Bramah's genius produced the hydraulic press, and he clearly foresaw the future development and great capabilities of his system; but it was reserved for Lord Armstrong to work out and superintend the intricate details that had to be developed before the system could be made fully serviceable. The public supply of hydraulic power in London constituted the latest development of this system. The hydraulic power was supplied through mains charged by pumping at a pressure of 700 lb. per square inch. The first and largest pumping station had been erected on a site known as Falcon Wharf, about 200 yards east of Blackfriars Bridge. The engine house at present contained four sets of pumping engines, each set being capable of exerting 200 I. H. P.
The engines were vertical compound, of a type comprising the advantages of a three-throw pump with direct connection between the pump plungers and the steam pistons. Each set of engines would deliver 240 gallons of water per minute into the accumulators at 750 lb. pressure per square in. at a piston speed of 200 ft. per minute. This was the normal speed of working; but, when required, they could be worked at 250 ft. per minute, the maximum delivery being 300 gallons per minute. The condensing water was obtained from storage tanks over the engine house, and was returned by circulating pumps to one or other of those tanks. The water delivered into the mains was maintained all the year round at temperatures of between 60° and 85°. The boilers were of the double flued Lancashire type, and were made of steel. All were fitted with Vicars' mechanical stokers. At the back of the boilers was a Green's economizer, consisting of ninety-six tubes. The economizer and the stoker gear and worm were driven by a Brotherhood three cylinder hydraulic engine. The reservoir of power consisted of accumulators. The accumulators at the pumping station were two in number, each having a ram 20 in. in diameter and 23 ft. stroke.
The weight cases were of wrought iron, and were filled with iron slag. The total weight of the case and load on each ram was approximately 106 tons, corresponding to a pressure of 750 lb. per square in. The storage tanks formed the roofs for the engine and boiler houses. The water for the power supply was obtained from the river Thames, and was pumped into the tank over the engines. The water passed through the filtering apparatus by gravity into the filtered water tank over the boiler house, which was 7 ft. below the level of the unfiltered water tank. The filters consisted of cast iron cylinders, and each contained a movable perforated piston and a perforated diaphragm, between which was introduced a quantity of broken sponge; the sponge was compressed by means of hydraulic pressure from the mains. The delivery of power water from the Falcon Wharf pumping station was through four 6 in. mains. The most distant point of the mains from the accumulators was at the west end of Victoria Street, and was 5,320 yards, or just over three miles. To provide for all frictional loss in the pipes and valves, the accumulators had been loaded to 750 lb., the stated pressure supplied being 700 lb. per square in. The total length of the mains at present laid was nearly twenty-seven miles. The mains were laid in circuit, and there were stop valves at about every 400 yards, so that any such section of main could be isolated.
The method employed for detecting leakage was based upon an automatic record of the number of gallons delivered into the mains, and in cases of abnormal increase during the night, if found to arise during the early hours of the morning, the mains were tested. The power water used was invariably registered through meters on the exhaust pipes from the machines, and from the meters passed to the drains. There was a sliding scale of charges from 8s. to 2s. per 1,000 gallons at 700 lb. pressure per square inch, designed to meet, as nearly as possible, the variable conditions and requirements of consumers. The more continuous the use, the lower the charges. The scale was intended chiefly for intermittently acting machinery, and experience had fully proved that these rates were sufficiently low to effect a large saving to the consumer in almost all cases, whether for a large or a small plant. The author believed any idea of supplying power from a central source at rates much below these to be chimerical. The practical efficiency of the hydraulic system might be fixed at from 50 to 60 per cent. of the power developed at the central station. No other method of transmission would, he thought, show a better result; and the general convenience and simplicity of the hydraulic system were such that its use would hardly be affected, even if there were no direct economy in the cost of working.
In addition to the general supply of hydraulic power, in the City and adjoining districts, to the six hundred and fifty machines at present worked, a new departure had been taken by the application of hydraulic power to an estate at Kensington Court—the name given to an area of about seven acres opposite Kensington Gardens. Seventy houses and dwellings were to be built on this estate, of which thirty had been already erected. Each house was fitted with a hydraulic lift, taking the place of a back staircase, and the power supply was provided on the estate expressly for working these lifts. The driven machinery was of as great importance to an economical and satisfactory result as the distributing plant, but this obvious fact was not always understood. General regulations had been prepared by the author, defining the conditions to be observed by manufacturers in fitting up machinery for connection to the power mains.
They were intended to secure safety, and an efficient registration of the quantity of power used; but they left the question of the economy and of the efficiency of the machines to be settled between the consumers and the makers. In London more lifts were working from the mains and more power was used by them than by any other description of machinery. The number of all classes at present at work was over four hundred. The principal types in use were fully described. In some cases there had been, by adopting the public supply, a saving in the cost of working of about 30 per cent., as compared with the steam pumping plant previously in use.
Lifts were now becoming so general, and the number of persons who used them was so great, that the author considered it necessary to urge the importance of securing the greatest possible safety in their construction, by the general adoption of the simple ram. Suspended lifts depended on the sound condition of the ropes or chains from which the cages hung. As they became worn and unreliable after a short period, it was usual to add safety appliances to stop the fall of the cage in case of breakage of the suspending ropes; but they could not be expected to act under all circumstances. As an indication of the important part which lifts occupied in a modern hotel, it might be mentioned that at the Hotel Metropole there were, including the two passenger lifts and that for the passengers' luggage, no less than seventeen hydraulic lifts in use day and night, while the work done represented about 2,000 tons lifted 40 ft. in this time. The next largest use of the power was for working hydraulic cranes and hoists of various kinds along the river side, and in the city warehouses. It often happened that the pressure in the power mains was not sufficient for pressing purposes.
The apparatus known as an intensifier was then used, by which any pressure required could be obtained. Hydraulic power was also used at Westminster Chambers, and elsewhere, for the purpose of pumping water from the chalk for domestic use. The pump was set going in the evening and continued working till the tanks were full, or until it was stopped in the morning. For work of this kind, done exclusively at night, a discount was allowed from the usual rates. Mr. Greathead's injector hydrant, made at the Elswick works, had been in use to a limited extent in London in connection with the power mains.
A small jet of high pressure water, injected into a larger jet from the water works mains, intensified the pressure of the latter in the delivery hose, and also increased the quantity. By this means a jet of great power could be obtained at the top of the highest building without the intervention of fire engines. This apparatus enabled the hydraulic power supply to act as a continuous fire engine wherever the mains were laid, and was capable of rendering the greatest assistance in the extinction of fire; but there was an apathy on the subject of its use difficult to understand. In Hull the corporation had put down a number of these hydrants in High Street, where the hydraulic power mains were laid, and they had been used with great success at a fire in that street. The number of machines under contract to be supplied with power was sufficient, with a suitable reserve, to absorb the full capacity of the station at Falcon Wharf, and another station of about equal capacity was now in course of erection at Millbank Street, Westminster. The works had been carried out jointly by the author and Mr. Corbet Woodall, M. Inst. C. E.; Mr. G. Cochrane had been resident engineer and superintendent. The pumping engines, accumulators, valves, etc., and a considerable portion of the consumers' machinery, had been constructed at the Hydraulic Engineering Works, Chester. Sir James Allport, Assoc. Inst. C. E., who was the first to adopt hydraulic power for railway work, had been associated with the enterprise from the commencement of its operations in 1882. His wide influence and extended experience had greatly assisted the commercial development of the undertaking.
TEST OF A WROUGHT IRON DOUBLE TRACK FLOOR BEAM.[1]
By Alfred P. Boller, Mem. Am. Soc. C. E.
Testing to rupture actual bridge members is always a matter of great scientific interest, and while the record is quite extensive in eye bars, posts, or small parts, the great cost, time, and inconvenience of handling heavy girders has prevented experiment in that direction. In fact, the writer is unaware of any experiment upon compound riveted beams on a large scale, as actually used, until the experiment recorded below was made under his supervision. The beam was an exact duplicate of those in use on a bridge, about which more or less controversy had arisen as to their practical safety, and the test was made under, as near as possible, actual conditions of attachment and loading. The annexed drawing shows the form and proportion of the beam and connection with the posts, together with the position of the track stringers. The actual static loads to which the beam could be subjected by the heaviest engines in use on the road, with weight of floor, is 40,000 lb. at each stringer bearing, the strains computed therefrom being as follows: Flange strains at m, 3,800 lb. per square inch; at a, 5,700 lb. per square inch; at b, 6,400 lb. per square inch. Shear strains in web, between a and b, 2,600 lb. per square inch. Shear strains in web, between a and end, 8,000 lb. per square inch at least section, or where the web is 2 feet 4 inches deep, or 42 diameters between angle iron.
[1] Abstract of a paper read before the American Society of Civil Engineers, November 16, 1887.
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