The Automatic Stoker, Though not Strictly a Fuel-
GENERAL VIEW OF THE DU PONT-
1. Feeder trough for tender. 2. Stoker driving-
AMONG the many locomotive developments, which have been advanced to a high standard of reliability, must be mentioned the mechanical method of feeding the hungry furnace with a steady and continuous stream of coal in order to maintain the desired head of steam under fluctuating conditions. In those countries where fuel-
All railways are not in the position to use oil-
The locomotive builders responded, but in remedying one evil they created another. They increased the dimensions of the boiler, and also those of the fire-
Under concentrated study and experiment evolution was rapid. In the course of two or three years there was a multiplicity of appliances for mechanically firing the locomotive. This activity was enthusiastically stimulated by the railways, and facilities for subjecting the various conceptions to trial were readily granted, but the great majority have been found wanting. The result is that, to-
REAR VIEW OF DU PONT-
Shows the tender trough, crusher plate, part of horizontal conveying system and the method of driving.
The task is invested with many interesting and intricate problems, but there are three of cardinal significance; if they cannot be solved the conception is doomed to failure. In the first place, it is obvious that to bring the dense solid fuel to the comparative mobile level of a liquid it must be reduced to a fine form -
Secondly, as the crushing component of the machine must necessarily be contiguous to the coal supply carried in the tender, while the furnace-
The railways promptly turned to the automatic stoker when it had established a sufficient degree of utility, and locomotives equipped therewith made their appearance upon the various American railways. But to general surprise the results were markedly disappointing. Forthwith, an elaborate investigation was instituted. Scientific tests conducted at the University of Illinois proved highly illuminating and yet disturbing. A considerable proportion of the fuel delivered into the fire-
SCHEMATIC DIAGRAM SHOWING FIXING OF DUPLEX STOKER TO THE LOCOMOTIVE
The conveying and elevating screws, and the tube opening at the top of the elevator, through which the crushed coal is blown into the fire-
This discovery led to further diligent investigation of the effectiveness of the stokers in use, and results were found to be corroborative. The earlier types of machines were discovered to be the worst offenders; some of them wasted as much as 40 per cent of the fuel fed to the furnace, while the losses through the smoke-
The reason was ascertained. The fine particles, being relatively light and introduced into the fire-
The majority of the machines fed the coal at the approximate level of the arch within the box, and so met the stream of gases near the point where they were swirling round the deflexion, to be swept over the top of the arch into the tubes. From the observations made, the investigators came to the further conclusion that the manner in, and the height at, which the coal was introduced into the fire-
As the result of these searching inquiries the development of an “underfeed” type of automatic stoker was advocated. Now the majority submitted for trial were of the “overfeed” design -
The du Pont-
This stoker comprises two main elements -
blade forming a screw conveyer; the latter is so placed in the former, and the whole so housed, as to minimize the possibility of foreign substances falling into the trough and working under the screw, thus causing it to jam and stop.
DIAGRAMMATIC VIEW OF FIRE-
This shows the manner in which coal is spread over the grate area, and the method of lifting the crushed coal from the hopper into the distributor tube.
At the forward end of the trough is a plate carrying a number of inwardly projecting spikes. The coal, dropping into the trough and advanced through the latter by the action of the helicoidal screw, forces the lumps against this crusher plate, and under the pressure exerted the masses are split into small pieces. This crushing action is continued until the coal has been reduced to sufficiently small size -
The main conveyer-
intermediate section with universal and ball joints at each end, with a central sliding joint in the centre. This permits the stoker to adapt itself to the sharpest curve traversed by the locomotive, and, through the sliding joint, enables the two sections to come adrift instantly.
At the forward end is the distributor. This comprises a vertical cylindrical housing carrying a vertical lifting screw. The coal thus raised overflows, or spills, on to the protecting grate, or, as it is called, the firing-
SCHEMATIC DIAGRAM OF ELVIN MECHANICAL STOKER SET IN POSITION ON THE LOCOMOTIVE
1. Stoker. 2. Deflexion plate. 3. Elevator. 4. Shovel for throwing coal into the fire-
The vertical housing above the grate level is surrounded by a protecting grate set a few inches away. Its purpose is to safeguard the first-
The operation of the stoker is carried out by means of an independent motive unit. This is a slow-
The volume of coal fed to the fire-
In determining the height for the delivery of the pulverized coal into the fire-
SIDE VIEW OF COMPLETE ELVIN AUTOMATIC STOKER
On the left, the element carried upon the tender of the locomotive with its drive; on the right, the section fitted to the boiler back-
crushed coal is moved forward.
It must not be thought that the automatic stoker completely displaces manual labour in firing the engine. It is preferable that the fire should be started and maintained by hand in the usual manner until the locomotive has been coupled up and the train has started on its journey. Once the stoker has been set in operation, and the jets adjusted, no further variation is required, although, after starting, the fire should be examined occasionally to see how it is burning, and the control varied accordingly.
The flow of the coal and speed of the conveyer can be ascertained by peering through the grating in the forward housing. Should the rotation of the screw be momentarily arrested the fact is revealed by a rise in the pressure of the steam-
The Elvin Automatic Stoker
The mechanical shovel method of distributing the coal into the fire-
This apparatus similarly comprises two fundamental elements -
This sectional view shows the alternately oscillating mechanical shovels, and how coal raised through the elevator to the table is swept forward into the fire by each stroke.
It is not necessary to pass all coal through the crushing process. An appreciable quantity has already been reduced to the desired size in the handling between the mine and the locomotive tender. This is permitted to drop through suitable slots into the hopper beneath before the crusher is reached. Owing to the feeder having only an intermittent movement, and one which does not exceed a maximum of 1½ inches per impulse -
The breaker is of the reciprocating type which has been used for years for a similar purpose in a variety of industries, and so is a well-
A short distance beyond the crusher are the coal-
The pulverized coal, collecting in the hopper beneath the cylindrical feeder trough, is led to the stoker unit through an inclined screw-
The shovels (small arms with a scoop) are mounted on either side of the opening through which the coal is delivered by the stoker elevator. They sweep to and fro alternately, as it were, across the table towards the fire, so that any coal raised to the table, irrespective of its quantity, must be swept into the fire. Furthermore, the shovels have accelerated and retarded motions imparted to them mechanically, such as will ensure the correct distribution of the fuel.
LOCOMOTIVE CAB SHOWING ELVIN STOKER IN POSITION
This distinctive shovel movement is accomplished by means of a very simple and substantial action. Approximately in the centre of the stoker-
The stoker is driven by a simple, compact and efficient engine. This is of novel design with a double reciprocating square piston. It has no dead centre, and can be started, stopped or reversed instantly by a convenient throttle and reverse lever. There are no eccentrics, or piston-
The engine is completed with a governor to compensate for the fluctuating load on the stoker engine, arising from the varying strain imposed upon the coal crusher, according to the character of the fuel in use. This is also of novel design. It has been introduced to maintain a uniform working speed on the stoking shovels, and its most notable feature is a variable speed-
ELVIN MECHANICAL STOKER FITTED TO A “MALLET” LOCOMOTIVE
This engine furnishes the power for operating the drag chain, feeder, and coal crusher on the tender, the screw-
The coal is distributed in the fire-
The volume of coal delivered to each shovel can be varied from a few ounces to about 7 lb, and is thrown into the furnace at the rate of 36 to 40 shovels per minute. Delivery of the coal in correctly adjusted and distributed charges is most favourable to economical consumption. At the same time it gives a lire which throws off little smoke, and reduces the losses through the smoke-
In designing the stoker the question of weight has received full consideration in order that the load imposed upon the trailing wheels may not be rendered excessive. The total weight of the firing element, including its engine, fitted to the Chinese “Mallet” already mentioned, is less than 3,000 lb. Suitable provision is also made for the displacement between locomotive and tender when travelling round curves, as well as for ready disconnexion when the tender is drawn back for inspection of the draught gear. The greater part of the machine is carried below the foot-
FEEDER TROUGH OF ELVIN MECHANICAL STOKER FITTED TO LOCOMOTIVE TENDER
The coal is moved forward over the four travelling chains to the front end of the trough against the coal-
The operation of this mechanical stoker is solely dependent, after it has once been set in motion, upon the manipulation of the speed-
The task imposed upon the fireman, in so far as stoking is concerned, is as simple as could be contrived; he is not called upon to leave his seat unless something unexpected supervenes. He need not move to ascertain how much coal is being fired, since he has only to turn his head to observe the quantity being brought forward with each movement of the feeder chain. There is no necessity to open the door to look into the fire-
In the same way he will speedily master the speed at which the stoker should be run in order to gain the most satisfactory results. This factor is dependent upon the size of the fire-
The steam method of distributing the pulverized fuel in the fire-
The tender component consists of a heavy wrought steel trough, fitted with a helicoidal screw, which moves the coal, falling into the trough, forwards, into the crushing zone with its crushing plate, where the lumps are reduced to the desired size. This unit does not belong to the tender but to the engine, so that when the connecting gear is released, to allow the tender to be drawn back, the latter comes clear of the stoker-
End view, showing method of mounting to boiler back-
The coal is fed forward to a transfer hopper, having a dividing rib, flexibly connected to the conveyer by a ball-
Upon reaching the top of each elevator the coal drops into the elbow, which is really the distributor, because thence the fuel is blown into the fire-
Distribution of the coal is varied by adjustment of the steam-
ATTACHMENT OF DUPLEX STOKER TO BACK-
Showing trough with helicoidal screw fixed under tender by which coal is carried forward against crusher plate; also two vertically inclined elevators which lift the coal to the fire-
The stoker is driven by a single-
The Duplex Stoker will handle all varieties of coal, from the hardest of lump to wet slack, with equal facility. It occupies but little room in the cab; the impingement upon the space in which is confined to the two elevator casings projecting a short distance above the deck, and close to the back-
According to the experience which has been accumulated any locomotive performing passenger or freight duty, having a maximum tractive effort of 50,000 lb, or burning upwards of 4,000 lb of coal per hour for an extended period, should be equipped with a mechanical stoker. Of course, in excessively warm climates, or at high altitudes, where manual stoking is exhausting, the practice may be profitably applied to locomotives of smaller dimensions.
It is necessary to point out that the mechanical method of firing the locomotive does no more than relieve the man of arduous work. It is not a fuel-
Although the mechanical stoker is practically depriving the fireman of his essential job, it is to the distinct advantage of the man and the efficiency of the locomotive in general. This method of firing is not only cleaner and easier, but it enables the fireman to assume more responsible duty and conduces to the enhanced safety of the train. Two men are available to watch the signals. Finally, the fireman has the opportunity to acquire a superior training for his ultimate position of driver.
SETTING THE DUPLEX STOKER
The engine which drives the stoker is seen on the left at the base of the unit. A huge “Mikado” locomotive carries the device.
[From Railways of the World by Frederick A. Talbot, published 1923]