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as it has to be whenever the rods have to be taken down. While the construction at the guide yoke appears to be very heavy and cumbersome, a careful examination of the drawings will show that it is really more simple than in previous designs of this valve gear, which were more open.
The most widely different classes of service have been represented thus far in the showing of modern engines that are equipped with Walschaert's valve gear, but as a further illustration of its adaptability to various conditions without serious alteration from the simplest design, as well as to bring to notice the fact that European railways are taking advantage of the possibilities that lie in the use of this gear, Fig. 21 is presented as one of a group of thirteen engines that were exhibited at the Exposition held at Liege in 1905, by the State Railways of Belgium—the same road that graduated the inventor of the motion—and this may be said to be a lineal descendant from Walschaert's successful experimental engine of 1848. It was constructed by the Societé Anonyme la Meuse, of Schenien, from the designs of M. Flamme, General Inspector, under the direction of M. Bertrand, Director of the State Railways, and is one of a number of engines built for experimental purposes.
The plate is reproduced directly from the June, 1906, issue of the American Engineer and Railroad Journal,
and represents a 4-6-2 engine with four simple (“simple,” as the reverse of “compound,” refers to the direct use of boiler pressure in all of the cylinders of the engine: where, no matter how many cylinders there are, their pressures are exhausted after the first expansive use) cylinders arranged on a horizontal line that centres through all four pistons and the main shaft, or axle; the main rods from all of the cylinders drive on the front axle, two of the cylinders outside of the frames—one on each side of the engine—having their main rods attached to the crank-pins, while the other two cylinders inside the frame are connected with a built-up crank axle; but with reference to their points of connection on the main axle the cylinders are arranged in pairs, the outside cylinder on each side and the one next to it just inside the frame are paired, with the crank-pin and the crank axle of each pair set 180 degrees apart, or just opposite each other on the shaft. With all moving parts in the cylinders, and the main rods, being exact duplicates in the matter of weights per pair, the motion on each side of the engine is perfectly balanced. The paired cylinders on one side of the engine are connected with the main-pin and axle crank at 90 degrees from the connections of the corresponding pair of cylinders on the other side for the same reason that the two main pins of the common two-cylindered engine are always set quarter
ing to each other-so that both forces can never be on the dead-centres at the same time.
This plan of arranging the four cylinders and their delivery of power is being used on some of the most recently built American locomotives, but our engines are compounded, only two of the cylinders receiving boiler pressure direct: the Vauclain Balanced Compound, and the Cole Balanced Compound, both previously noted, are of this type, with the large, lowpressure or second-expansion cylinders outside the frame, and the smaller, high-pressure or first-expansion cylinders located inside, or between the frames; in starting a train-particularly a heavy one-the power of the cylinders termed high-pressure is temporarily suspended, thus removing an immensely twisting effect from the cranks in the axle at a critical time, and full boiler pressure at long cut-off is admitted to the large cylinders outside of the frame. After the train is under way, and the action is changed to com pound, the inside cylinders receive direct boiler pressure and exhaust it into the large, outside cylinders in which the final expansive power of the steam is obtained, and from which the exhaust to the atmosphere takes place.
If the Stephenson valve gear is used on engines of this type it necessitates placing the eccentrics on some other than the crank axle, for there will not be room
left after considering the main cranks; and taking the power to actuate the valve from any other pair of wheels is highly undesirable, both on account of the extra amount of lost motion introduced and the entire disability of the engine in case one side rod should break, if it should be the section between the wheels to which the main rod is attached and the pair carrying the eccentrics-on either side of the engine. The application of the Walschaert gear eliminates the possibility of such troubles, as this gear has no dependence on the axle for anything, and the eccentric can always be placed on the main pair of wheels.
The assertion that the Walschaert valve gear can be applied to engines of odd design without addition of complicated parts, where the Stephenson motion would have to include so much more weight of metal as to be almost prohibited, is proven in the case of this Belgian engine in Fig. 21.
In this engine live steam is used in all of the four cylinders and the operation of each is controlled by a separate piston valve of inside admission-a design of valve quite unusual in European practice—and both valves on each pair of cylinders are actuated by but one set of Walschaert's gear.
To glance at the set-up of the gear in Fig. 21,--the eccentric placed ahead of the main pin and the valvestem connected the extreme top end of the com