bination lever-one would think that outside admission valves were indicated, but in this case things. are not as they appear to the eye: the motion of the FIG. 24.--Side Elevation Diagram of Belgian Engine. FIG. 25.-Plan Diagram of Above. combination lever is not given to the stem of the outer piston valve, but is transferred through a rocker-arm to the valve operating the other cylinder of the pair the one inside the frame-and as the main rod from the inside cylinder is connected to the axle crank exactly opposite the main-pin connection of the outside cylinder-180 degrees apart-the set-up as shown is correct in its action on the inner half of the motion on that side of the engine. Now, in order to supply a satisfactory motion to the valve of the outside cylinder it is only necessary to give it an exactly opposite movement to that of the inner one, and this is easily accomplished by extending the stem of the inner valve through the front head and connecting it to a lever that extends across the frame, a pin in the exact centre of the lever and a bracket attached to the frame forming its fulcrum, and to the other end of this lever is connected the extended rod from the outer valve, which also passes through its front steam-chest head. This action is the same for the pair of cylinders and valves on each side, and in the sectional views, on folding plates, Figs. 22 and 23, and the diagrams, Figs. 24 and 25, the valve connections are clearly seen. In American practice the rocker-arm would undoubtedly be dispensed with, further simplifying the motion, and the gear so devised as to operate the outside valve and cylinder direct, using the lever connecting the extended valve-stems to actuate the inner valve. The diameter of the cylinders is reduced to an extent that both pistons of one pair have an area exposed to steam pressure of about the same number of square inches as would be contained on a single piston of an ordinary two-cylindered engine of the same weight and steam-generating capacity, and therefore the amount of steam consumed is the same for each type of engine, but this Belgian locomotive with four cylinders is perfectly balanced, and the rods, pistons, etc., need not be much over one-half the weight of the corresponding parts of a two-cylindered engine. To the name of Egide Walschaerts belongs the credit and the honor of having first conceived the principle of the valve gear that rightfully bears his name, but that principle has been more highly developed by others, until the device as it is applied to locomotives at the present time is practically perfect; but in order to show that there has been no actual change in the original Walschaert theory, the following bit of history is here reproduced from the Railroad Gazette of November 24, 1905, and is contained in an article on the life and works of the inventor, by Professor M. J. Boulvin of the University of Ghent: After Walschaert had obtained (through the assistance of his friend, M. Fischer) his Belgian patent, he took out another patent for the same invention, on October 25th of the same year, in France. There also exists among the documents left by the inventor a contract signed by Demeuldre, at Brussels in 1845, from which it appears that he undertook to obtain a patent of importation into Prussia for the new valve motion, subject to an assignment by Walschaert of half of the profits to be deducted from the introduction of the new valve motion in that country. It is probable, however, that this contract was never carried out. The design attached to the Belgian patent is reproduced in Fig. 26. In this primitive arrangement the link oscillated on a fixed shaft, in regard to which it was symmetrical, but it had an enlarged opening at the centre so that only at the ends was it operated without play by the link-block, which was made in the form of a simple pin. There was only one eccentric, the rod of which terminated in a short T carrying two pins. The reverse shaft operated the eccentric rod and maintained it at the desired height. For one direction the lower pin of the T engaged in the lower end of the link, and to reverse the engine the rod was raised so that the upper pin engaged in the upper end of the link. The angle of oscillation of the link varied with the position of the pin in the link, and this oscillation was transmitted by an arm to the combination lever, which was also operated by the crosshead. |