eccentric rod and the valve-stem, yet the design of the locomotive often requires an arrangement similar to that shown above. The system which Mr. Heusinger Von Waldegg invented in 1849, and which he applied in 1850 to 1851, differs only in a few insignificant particulars from that shown in Fig. 27. Walschaerts had therefore preceded him. SECOND DIVISION DESIGNING AND ERECTING THE WALSCHAERT VALVE GEAR. WHEN a newly equipped engine with Walschaert valve motion is received by a railroad and after the gear has been set up complete at the roundhouse, everything should be carefully inspected, with the view of securing a perfect initial adjustment of the entire valve motion, and to eliminate, if found, any slight error whatever while the other parts of the motion work of the engine are new and of perfect fit and properly adjusted all around; especially in regard to the driving-boxes, rod brasses, and other bearings. It must always be remembered in setting the Walschaert valve gear that two otherwise separate and distinct motions are now brought into a working combination with each other in order to produce the desired movements of the valve, and these two motions are due to the piston's travel, delivered through the crosshead connection, and the throw, or turning movement, of the eccentric. The piston's motion really governs the lead by offsetting the valve from its central position far enough to overcome its steam lap and enough further to give the amount of port opening desired for lead, and it will do this in both front and back positions of the piston, the lead being the same at the beginning of each stroke, both forth and back. The piston must move the valve in a direction opposite to its own position in the cylinder to secure lead with outside admission valves, but the piston must draw the valve further in the direction the piston lies in-toward the end of the cylinder-to give the advance for lead with a valve of inside admission; and this principle is made plain by the diagram in Fig. 28, in which it is seen that the piston is connected to one end of a common lever, and the connection to the valve-stem is either at the extreme opposite end, or at an intermediate point on the lever, according to whether the valve is of outside or inside admission. There are three points to a true lever, however, and the third point on the combination lever is its connection with the radius rod-the point where the valve, through the combination lever, receives the greater part of its motion due to the eccentric's action. In Fig. 28, two combination levers are represented as being actuated by the piston and two radius rods, and are operating two valves,-one with inside admission and the other with outside admission; the latter, and upper, valve has its stem and the radius |