Locomotive Stokers. The amount of water a locomotive boiler is capable of evaporating is limited by a number of conditions. It is possible to construct a locomotive of such dimensions that it would be capable of burning an amount of coal which would be physically impossible for a fireman to handle. Furthermore, the different methods of firing a locomotive by hand, as practiced by many firemen, are frequently very uneconomical and result in a great loss of fuel. Again, there are certain heavy freight runs on some railroads which require two firemen in order to get the train through on schedule time.
The above reasons and many others which might be mentioned have resulted in a demand for some form of automatic or mechanical stoker for locomotive work. In the last ten or fifteen years, much experimental work has been done along this line and a number of different types of stokers have been developed which have met with some success.
A locomotive stoker to be successful should meet the following requirements:
- It should be able to handle any desired quantity of coal and at the same time call for less physical effort on the part of the fireman than is required in hand firing.
- It should be able to successfully handle any grade of coal.
- It should be able to maintain full steam pressure under all conditions.
- It should not become inoperative under ordinary conditions of service.
- Its construction should permit of hand firing to meet emergency conditions.
Of the many types of locomotive stokers which have been developed and tried out, the following makes are characteristic and will serve for illustration.
Chain Grate Stoker. The chain grate stoker, invented as early as 1850, was thought at first to have solved the smoke problem. It was used to a limited extent in and about New York City, but for various reasons was soon abandoned. Its construction was quite similar to our present-day chain grate commonly used in power-plant work. It was mounted on wheels and could be drawn out of the fire-box on a track. Coal was shoveled into a hopper by the fireman and the chain grate was operated by a small auxiliary steam engine.
Hanna Locomotiw Stoker. The Hanna locomotive stoker, developed by W. T. Hanna, is so constructed that the entire apparatus is readily applicable to any locomotive and is placed in the cab. It makes use of the ordinary fire door as a place through which the coal is jetted into the fire-box. It is operated by a small double-acting twin-engine placed in the floor of the cab, which serves to drive a screw propeller, which in turn causes the coal to be pushed upward and forward through a large pipe leading to the fire door. The engine can be reversed by means of a reversing valve, which changes the main valve from outside admission to inside admission.
Coal is shoveled into a hopper and from the hopper it is carried by the stoker mechanism to a distributing plate immediately inside of the fire door. From the distributing plate, the coal is thrown into the fire-box by the action of a number of steam jets which radiate from a central point on the plate. The speed of the small operating engine controls the rate of firing. Deflector and guide plates, located just inside of the fire door, are so arranged and under control of the fireman that the coal can be placed on any portion of the grate desired.
This stoker requires much physical work on the part of the fireman, since the coal must be broken into small lumps and the hopper kept filled. The larger lumps of coal will be deposited near the rear part of the grate, the finer particles being blown to the front portion. Much of the finer particles of coal will burn as dust and a part will be drawn through the flues without being burned at all.
Street Mechanical Stoker. The Street mechanical stoker consists of a small steam engine bolted to the top and left side of the back head of the boiler, which drives a worm gear and operates a chain conveyor. The conveyor bucket elevates the crushed coal from a hopper below and drops it on a distribution plate, located just inside of the fire door. From the distributing plate the coal is thrown into the fire-box by an intermittent steam jet, which is under the control of the fireman. There is a coal crusher on the tender, which is driven by another small steam engine. The coal, after being crushed, falls down a 45-degree inclined spout to the hopper below the deck. Some of the later designs use a screw propeller to carry the crushed coal from the tender to the hopper. The Street stoker does not require a great amount of physical work by the fireman. The large lumps of coal will fall near the rear portion of the grate as in the case of the Hanna stoker.
Crawford Mechanical Underfeed Stoker. The Crawford mechanical underfeed stoker, invented by D. F. Crawford, S.M.P. of the Pennsylvania Lines west of Pittsburgh, has been tried out on the Pennsylvania Lines and has given very satisfactory service. This stoker takes coal from beneath the tender and by means of a conveyor carries it forward to a hopper. From the hopper, two plungers, placed side by side, push the coal still farther ahead where two other plungers, one on each side, cause the coal to be pushed up through narrow openings to the ordinary shaking grate. Both the conveyor and the plungers are operated by a steam cylinder, containing a piston operated by the ordinary nine and one-half-inch Westinghouse air-pump steam valve. The conveyor consists of a series of lunged partitions, or doors, which carry the coal in one direction and slide over it when the motion is reversed. If the conveyor for any reason should become inoperative, a door in the deck can be opened and coal shoveled into the hopper below. If the stoking device should become inoperative, then coal can be fired by hand in the usual way. This stoker requires a minimum amount of physical labor from the fireman. It can be applied to any locomotive, but only at considerable cost. Its application reduces the grate area to a certain extent and thus reduces the steaming capacity of the boiler.
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