A Small Steam Mine Locomotive.
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A Description of a Self-propelled Rail Tractor for Use in a Coal-mine.
One of the chief difficulties in the way of producing a satisfactory sellcontained locomotive for employment in underground mines has, of course, /ways been tho danger accruing from the presence of fire-damp and other explosive gases, in various parts of the workings. Electric mine locomotives .Aaave been employed in many instances where the danger of fire has not been siximinent, and, in other cases, where the risk has been less pronounced, it lieris been decided to employ locomotives propelled by petrol engines.
An instance, however, has now come to Our notice where it was not admissible to employ a machine which used petroleum spirit as a fuel, and yet where there was practically no danger which would arise from the use of enaked flames in the workings. These conditions obtain in a certain coal mine in the neighbourhood of Clerkbeaten, where the coal is procured by miners who are not under the necessity of using safety lamps, but who work by the light of exposed candles.
Taking all these conditions into consideration, it was decided, if possible, to employ a suitable steam engine for hauling the small mine rolling stock over the rails underground. The principal limitation, with which constructors of suitable steam plant were confronted, was due to the small overall dimensions to which it was nece.saary to conform. The required locomotive had to fit a 16 in. rail gauge ; it bad to be not more than 6 ft. long, 2 ft. 8 in. wide and 3 ft. 6 in. high: and, in addition, suitable seating accommodation had to be found in this space for the driver.
This interesting little problem in design has been satisfactorily tackled by Messrs. David J. Smith and Co., of 58, Compton Street, Goswell Road, E.C., and in the shops of these makers, a representative of this journal was recently shown a completed locomotive of the Serpollet type which satisfactorily fulfils all the purchasers' requirements. We reproduce a photograph herewith, in order to indicate the machine's general appearance.
A stout channel-steel frame is mounted in an entirely-novel manner on two 3 in. axles, each of which carries two 18 in. wheels, whose width of tire is 21 in. It will be noticed that the side members of the frame are each supported by a central bracket on a kind of rocking arm, which serves the purpose of a double radius rod and so dispenses with the usual horn-block form of construction. At each end of each of these arms, an axle box is pivoted in such is way that the axles are allowed to ride in perfect freedom with regard to one another. The springing of the whole vehicle is insured by the provision of short helical springs, which are interposed between the ends of the arms and the side members of the main frame. The engine, which is slung in the middle of the frame, drives by means of a Brampton roller chain to the forward front axle, to which the back axle is connected, on the other side of the machine, by a coupling chain of The roller type. The engine is a genuine Serpollet, with four single-acting cylinders, with a bore of 3 in and a stroke of in.
The horse-power is rated at 10, at a working pressure of 600 lb. The unique characteristics of the Serpollet type of engine are too well known to demand a detailed description on the present occasion. Suffice it to say that Messrs. David J. Smith and Co. have not found it necessary to embody any alterations from the original design, so far as the engine itself is concerned. The boiler, too, is of a modified Ser pollet type, with a down-draught flue, the products of combustion being delivered direct on to the ground. To facilitate "lighting up," a flap, con structed in the main flue, is provided on the top of the steam generator. The original Serpollet burner has not been retained, but a more-modern pattern, of the trough type, has been adopted. The fuel is ordinary paraffin.
The exhaust steam is carried to a condenser placed in front of the locomo tive, and, from there, it returns to the main water tank. To assist in the cooling of the condenser, an exhaustdriven-turbine fan is employed.
The feeding of water and oil, to the Loiler and burners respectively, is effected by means of a small direct acting duplex donkey pump, from which, motion is also derived to ac tuate the mechanical lubricator. No attempt is made at automatic control of the water and fuel, but suitable hand-regulating devices are conveni ently arranged to enable the driver to effect such control at will. An ex ample of the original form of Serpollet safety valve is mounted on the special form of dashboard, which also accom modates the various fuel and waterregulating devices and the necessary pressure gauges. A screw-down brake actuates the Ferodo-lined shoes, which make con tact with the wheels on the near side of the vehicle. This provision is a standby to the more-normal method, i.e., the reversing of the engine, by which the locomotive as a rule will be controlled. It is almost unnecessary to add that the engine runs equally well in either direction, and that no reverse gear is required. With the type of power plant which is installed on this little engine, it is anticipated that, if necessary, very-high speeds could be attained on the rails, but it is interesting to note that, under contract, it will only be required to pull four tons at a speed of 12 m.p.h. There are practically no gradients in the mines, to which the locomotive has now been dispatched. The machine has been Ordered as a cheap alternative to a cable-haulage system.