M^'^ "7. ^ The Baldwin Locomotive Works Philadelphia, Pa., U. S. A. Walschaerts Valve Gear Code Word—RECUAMENTO Record No. 70 Revised and Reprinted 1913 PACIFIC TYPE LOCOMOTIVE WITH WALSCHAERTS VALVE GEAR CHICAGO AND EASTERN ILLINOIS RAILROAD Walschaerts Valve Gear SINCE the year 1905, the Walschaerts valve gear comparatively small wheels and are employed in high has come into extensive use in American loco- speed service. In the Walschaerts gear the various motive practice, and it is now more generally parts are pin-connected, and are easily lubricated; employed, especially on heavy power for road service, hence troubles due to heating are reduced to a minimum. than any other form of motion. The principal advant- The Walschaerts motion is of the radial type, and age of this gear lies in the accessibility of its parts, which it employs a link which is trunnioned at its middle point. are placed entirely outside the driving wheels. This The link is rocked by means of an eccentric rod, whose facilitates oiling, inspection and cleaning; operations motion is usually derived from a return crank, secured which are frequently difficult to carry out in locomotives to the main crank pin. The movement of the link is equipped with the Stephenson link motion. Further- transmitted to the valve stem by a radius rod, whose more, in heavy engines equipped with the Stephenson length is equal to the link radius. This radius rod is gear, the eccentrics must be made of large diameter pinned to the sliding link block, and can be raised or to secure the required throw. This increases the veloc- lowered by the reverse lever. When the block is above ity of the rubbing surfaces and also the tendency to the link center, the engine runs in one direction, and heat, especially in the case of locomotives which have when below the center, in the opposite direction; the THE BALDWIN LOCOMOTIVE WORKS FIG. 1 THE BALDWIN LOCOMOTIVE WORKS THE BALDWIN LOCOMOTIVE WORKS direction of movement being determined by conditions to the lap plus the lead, and the correct steam distri- to be subsequently explained. bution is secured. The return crank on the main pin (known as the The accompanyingdiagramsshow two arrangements eccentric crank) is so set that, when the piston is at the of Walschaerts motion. Figure i represents a design extreme end of its stroke, the link stands in its middle used with outside admission slide valves, and Figure 2 position; and it is evident that if the radius rod were a design used with inside admission piston valves. In attached directly to the valve stem, the valve would both cases corresponding parts are similarly designated also be in its middle position. When, however, the by letters, as follows: — piston is at the end of its stroke, the valve should be A valve — displaced from its middle position by an amount equal B valve stem — to the steam lap plus the lead. In the Walschaerts C combining lever — gear the valve is given lead by a combining lever, D crosshead link — which is attached to both the valve stem and radius E radius rod — ; rod, and is also connected, through a suitable link, to F reverse shaft — the crosshead. This combining lever is so proportioned G lifting link — H that if the point of its connection to the radius rod be reach rod — kept a stationary fulcrum, and the piston moved a dis- K reverse lever — tance equal to the stroke, the valve will be moved a L reverse link M— distance equal to twice the lap plus the lead. There- eccentric rod — fore when the piston is at the end of its stroke, the valve N eccentric crank is displaced from its middle position a distance equal The main pin is shown on the forward dead center, THE BALDWIN LOCOMOTIVE WORKS and the reverse lever is in its middle position, with the combining lever only, it is evident that the lead given link block in the center of the link. A careful study of by the Walschaerts gear is the same for all points of the diagrams reveals the following facts. cut-off. This is the principal feature which distinguishes — With a valve having outside admission this gear from the Stephenson motion as far as steam The valve rod is connected to the combining lever distribution is concerned. All parts of the Walschaerts at a point above the latter's connection to the radius rod. motion should be correctly laid out and constructed from a diagram, and the gear designed to give the lead most If the block is in the loiuer half of the link when in desirable for the usual running speed. The parts having forward gear, the eccentric crank leads the main pin. been correctly made, it is impossible to alter the lead If the block is in the upper half of the link when in without seriously deranging the motion. In this respect forward gear, the eccentric crank follows the main pin. — the Walschaerts gear is less flexible than the Stephenson; With a valve having inside admission but when the correct steam distribution is obtained it The valve rod is connected to the combining lever is less liable to derangement, and the engine is more at a point below the latter's connection to the radius easily kept "square." rod. The accompanying illustrations represent eight If the block is in the lower half of the link when in arrangements of this gear, as applied to recent locomo- forward gear, the eccentric crank follows the main pin. tives of various types. The styles shown are briefly If the block is in the upper half of the link when in described as follows: forward gear, the eccentric crank leads the main pin. Figure 3 shows the gear as applied to an American Inasmuch as the position of the valve, when the type locomotive, with slide valves. The link bearings piston is at the end of its stroke, is dependent on the are bolted to the guide yoke, and the reverse shaft THE BALDWIN LOCOMOTIVE WORKS bearings to a cross-brace placed immediately ahead of the main driving wheels. Figure 4 shows the gear as used on an Atlantic type locomotive. A cast steel bearer, placed between the two pairs of driving wheels, supports the link and re- FIG. 4 links are carried on longitudinal bearers, placed outside the leading pair of driving wheels. FIG. 3 verse shaft bearings. The valve is of the piston type, with inside admission; and as the radius rod is down in forward gear, the eccentric crank follows the main pin. Figure 5 shows an arrangement of motion as applied to a ten-wheeled locomotive with slide valves. The FIG. 5