« PreviousContinue »
machinery in the mill was connected, it got off at full speed, and the motion was accelerated to such a degree, as, from the centrifugal force it had acquired, to break the fly-wheel into a great many pieces before the fireman could stop the engine. The broken pieces of the ring and arms flew in all directions through the side walls of the engine-room, and also through the ceiling above. After the accident it was found on examination that the throttle valve was broken in two pieces, and was, consequently, rendered useless as a regulator. To prevent the recurrence of accidents of this nature, a very simple contrivance might be adopted, which is as follows:--Place an additional valve in the steam pipe between the boiler and the engine, as near the latter as possible; let this valve be wrought by an apparatus connected with the governor, so arranged that when the engine exceeds its fastest speed the governor balls, by their centrifugal force, would act upon the apparatus so as to shut the valve. This might be effected in various ways, and would prevent the engine from attaining such dangerous degrees of speed.
The common throttle-valve and governor is certainly a most admirable and efficient contrivance; but in cases like the present, when the valve happens to break, the governor loses all control over the engine. At this moment, the above-mentioned appliance would come into action, and check the engine in time. It is not uncommon to have a separate shut-off valve of this description applied to engines to be wrought by hand by the engine-man, and it is found to be a very convenient way of regulating the motion of the engine until the belts, &c., are put on, and the engine has its regular work to perform. All that I would suggest is, that this valve should be connected with the governor, or otherwise, so as to be self-acting when the ordinary throttle-valve is disqualified for performing its proper duty, which might happen when the fireman was negligent, or absent from his post; but it is easy to perceive that, independent of these contingencies, very little time indeed is sufficient to allow the engine (especially if in good working order, and lightly burdened,) to attain such a high velocity as to work destruction before the fireman could get it checked. The accident at Dundee is a verification of the truth of this remark. The poor fellow that lost his life was struck by one of the pieces of the fly-wheel when in the act of running from the lower flat of the mill to convey intelligence of the accident to the fireman; and sufficient time had not elapsed to afford an opportunity of shutting off the communication between the engine and boilers, by the valves generally placed on the top of the boilers for this purpose. Certainly, the ordinary way of stopping the engine might have been resorted to, viz., to throw the eccentric rod out of gear; but this was not done in time nor would it be likely to be attended to in most cases of this nature.
I may mention, in conclusion, that the engine was of twelve horse power. The fly-wheel had been found deficient in weight, and in conseqnence pieces were put on the ring to increase the momentum of it. The original ring was cast in six pieces, or segments, and held together by the arms, which were cast in one piece, overlapping the joints, and secured by bolts. On examining the fractures it was evi
dent the arms had broken first across where they joined the ring. In measuring the section of this part of the arms, and calculating their ultimate strength by Tredgold's rules for the strength of cast-iron, the centrifugal force, or tensile strain, must have exceeded 30 to 35 tons on each of the arms before they had given way. The wheel was 12 feet in diameter, and sufficiently strong, even with the enlarged ring, to withstand the strain upon it while the engine moved at its ordinary speed; this was proved by the experience of a considerable number of years.
C. Dundee, 25th December, 1844.
Glasgow Mechanic and Engineer's Magazine.
Locomotive Engine Explosions. We have to record the occurrence of the second important explosion of a locomotive boiler-for we reckon the boiler of the iron steamer Telegraph, a locomotive boiler in all essential respects—that has occurred in this country. It took place on the 11th ult., upon the Dover Railway, with the engine “Forrester," in connexion with a goods train of twelve luggage wagons, on its way to Dover. It is stated that two successive explosions took place, the second one being of by far the greater force. As soon as the steam and smoke had cleared away, the line was found to be completely blocked up with wagons, which were spread across the whole line, and piled on each other; the engine had gone over the viaduct, and was partially buried in the earth beneath, whilst the tender was hanging over the side of the viaduct, torn and folded together like paste-board, its carriage having fallen about twenty yards from where the engine lay. The engine-driver was found dead; the stoker was found nearly dead, with the whole of his jacket, except the cuffs, blown off his back, and was conveyed to Guy's hospital. A strict examination into the circumstances of the accident was instituted, and the result is shortly as follows:
The bursting of the locomotive being the supposed cause of the accident, their first object was to examine the engine as it lay imbedded in the earth. After getting off the viaduct it had pitched head foremost into the earth a depth of four feet, and then turned over. They found the fire-box was blown out, as well as the firebars, and the inner casing, between which and the outer casing the steam generated, were also torn away. The next point was to examine what effect the explosion had upon the viaduct, and the probable cause of the engine getting off the line. They found that there had been two explosions—the first apparently took place about eighty feet from the spot where the engine was lying. The fire-bars at the bottom of the fire-box had been blown completely through the viaduct into arch No. 134, making a hole three or four feet square. The second explosion, the more severe of the two, not only blew the firebox through the arch No. 133, but such was the force of the steam, that the engine “jumped,” and descended partly on the rails, and partly off, a distance of eight or ten yards, crushing the immense pieces of timber that supported the viaduct. It was deposed by Mr. Bury, of the firm Bury, Curtis & Kennedy, the makers of the engine, that he could account for the explosion only by the excessive pressure of the steam, arising either from want of freedom of the safety valve, or from a deficiency of water in the boiler.
Description of several WATER-Wheels called “ TURBINES,” exhib
iled at the Exposition de l'Industrie Française, at Paris. Knowing the earnest desire of the scientific public for information, and the interest which attaches to French ingenuity and mechanical skill, we have availed ourselves of the valuable reports of M. Burat, C. E., to give an account of some of the most remarkable and interesting objects exhibited at the recent Exposition de l'Industrie Française, at Paris. A feature quite novel to us is the number of turbines exhibited, a class of machine, of which, we believe, no specimen exists in England, and of which the only description is a slight sketch by Mr. George Rennie, C. E., who has not, however, introduced any mention of it in his edition of Buchanan's Millwork. In France, however, we suppose that at least a hundred must be now in operation, and they must undoubtedly be successful, or they would not so early have secured the patronage of a class so prejudiced as the French millers.
Hydraulic Machines.-Not the least interesting section of the Exposition was that devoted to hydraulic apparatus. The rapporteur, in introducing the subject, says—“Many people imagine that the first cost and fitting up an bydraulic motor are less than those of a steam engine. What has had a great influence in propagating this error has been that the establishment of hydraulic motors generally took place under such unfavorable conditions, and on such a defective systein, that the first expense was diminished at the expense of the power of which only a third, or fourth, was utilized. When, however, we calculate, beyond the purchase of the right of water, and the adjoining ground, the construction of dams, head of water, mill race, and wheel well made, we shall find that for an equal amount of power, the fitting up of a steam engine is less expensive. The advantage, however, of hydraulic motors is, that though the cost of establishment may be considerable, the cost of maintenance is next to nothing, and the charge only the interest of the money laid out.” It is calculated that the amount of water power utilized in the factories of France is equal to 20,000 horse power, though from the bad construction of the machinery it is supposed to be under estimated, and that the real power of the water is at least double.
Many endeavors have been made by men of science to improve this state of affairs, and latterly, a great deal of attention has been directed to the turbine. Under the general name of turbine are included water-wheels formed on very different principles, and which have nothing in common but the property of all turning on vertical shafts. M. Burdini, mining engineer, first imagined and made known, under the name of turbine, machines which received the water in the upper part of a vertica! cylinder, or drum, and eject it from the lower part; the water is guided by vertical channels in the rim of the drum, which must have a height equal to half the entire height of the available fall of water.
M. Fourneyron has occupied himself a good deal with turbines, and the model of one erected at the mills of St. Maur, near Paris, was exhibited. In Fourneyron's turbine the drum is always made rather narrow. The water glances obliquely in horizontal jets on the whole contour of an internal vertical cylinder, and penetrates in every direction the compartments of the wheel, which, in turning, just touches this external cylinder, and follows by passing the curved buckets, or chambers, enclosed in the horizontal bases, and escapes horizontally from the external rim of the drum.
The construction of turbines suggests the most complicated problems of hydraulics, and theory has not yet afforded the means of solving them a priori ; practice alone gives any solution at present. The greatest difficulties in the turbine are in the details of execution. The water to produce the maximum effect must enter without shock, and leave without velocity. M. Fourneyron has constructed several turbines, but he has not made known the proportions which he gives to them. From the experiments of M. Savery, it was established that even with falls so slight as one foot, up to 3, 10, 15 and 25 feet, the disposable work transmitted by the turbine reached from 7 to 8-tenths of the motive power.
Turbines, of all hydraulic wheels, are those which under the smallest volume of water utilize the greatest quantity. The water which propels them does not press on the axis. The high and variable speed which can be given to them, without sacrifice of power, allows the abandonment, in many factories, of a quantity of mill work and heavy spindles, for the purpose of accelerating the movements. Another property of the turbine, and perhaps the most important, is that of working when it is completely immerged in the stream a fraction of the absolute power at least as great as when working above. This allows, at all times, the whole fall of a stream to be turned to account. From this property, M. Arago has conceived the plan of establishing a complete system of turbines on the Seine, in order to provide for the supply of water to Paris.
M. Fontaine Baron has sent to the Exposition a turbine of 18 h. p., which much resembles that of M. Fourneyron, though differing in some details, and particularly in the direction given to the chambers, or buckets. M. Fontaine, who lives at Chartres, has already constructed thirty or forly in that part of France, where the corn trade is a principal one. M. Taffe has frequently applied a register to M. Fontaine's machine, and certified the useful effect to be seventy-nine per cent.
Koechlin's Turbine.-M. A. Kechlin also exhibited a turbine patented by him, the construction of which consists of two hollow
conical centres surrounded with helical blades a and d, the upper one d, is fixed, and serves as a guide for the flow of water on to the blades of the lower one a, called the turbine; by the force of the current the
Fig. 3. water causes the turbine to revolve, and with it the vertical shaft on which it is keyed, and the beveled wheels above. Both the fixed and movable turbines are placed within the mouth of a tube, the orifice of which is contracted in such a manner as to allow the proper quantity of water to pass through, that is due to the velocity arising from the difference of two levels of water above and below the turbine. The advantages of Koechlin's turbine are, that the turbine may be placed at any point taken in the height of the fall according to