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be the chief and most interesting features of any treatise on this type of valve motion that could be written, and are reproduced directly from the models used in designing the valve gear at the greatest locomotive works in the world.

It would be natural to presume that the reader of this book, with interest enough in the Walschaert gear to prompt him to make an effort to secure information in regard to that style of valve motion, would already be possessed of at least a fair working knowledge of the principles of the common valve itself; therefore, the valve is herein treated superficially, except in its actions that may be peculiarly induced by the motion of the Walschaert gear.









FROM the time of the building of the first locomotive engine, the methods employed to actuate the valve that is required to supply steam from the boiler to the cylinder, and discharge it therefrom after it has performed its work, were experimental and crude, until along about the year 1840 the double-eccentric hookmotion had naturally evolved into the shifting link action, under the name it has ever since borne—the Stephenson link motion; and in spite of our general lack of conservatism, that gear is, to-day, the vital part of practically all American locomotives, although our engines have increased in weight during recent years to such an extent that the necessary enlargement of the parts of the valve motion has given them a tonnage to be started and stopped twice in every revolution of the driving wheels that should have prohibited the use of such heavy reciprocating parts before now.

. For this and other reasons, our locomotive builders have been casting about for some time in search of a valve gear more suited to modern conditions, with the result that many railroads have recently received new engines equipped with what is known as the Walschaert valve gear, a motion that was originated almost as long ago as the Stephenson link, and that has been in continuous and highly satisfactory use on European railways ever since; given desultory trials in America at intervals in the latter part of the last century by those prejudiced toward it, and dropped from sight, it has risen into our view again through a sheer necessity, and there is a general desire, now, to get acquainted with the principle of its operation.

About the year 1844—the transition period in the development of valve motions from the undecided to the accepted principles—Mr. Egide Walschaerts (the final s in his name has been dropped in its application to that type of valve gear), who was acting at that time as Master Mechanic of the Belgian State Railways, seems to have been dissatisfied with the results obtained from the use of two eccentrics in governing the motion of one main valve, and most likely foreseeing the possibilities in the line of economy by using the expansive power of the steam in the cylinders—something that had always been impossible of attainment with the hook motion-he invented the form of valve gear that

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