« НазадПродовжити »
through, or lashing the bell-crank arms to the gear frame. Then move on, with the valve having the short lap-and-lead travel as heretofore explained. If the rocker arm E of the bell crank should break off, proceed in the same manner, after removing broken parts and the transmission bar and eccentric rod.
Q. 8.-If the bell crank should break, how do you fix things?
A.-If the upper, or rocker arm E of the bell crank is broken, get the answer in the preceding question. If the vertical arm fails, the main-valve rod and the compression-valve rod must be disconnected from the combination lever and tied up to clear other parts, and the combination lever and crosshead link must come down; then block the main and compression valves, and proceed on your way—on one side.
Q. 9.—How can you provide for getting along with a broken combination lever?
A.-About the only thing to do is to remove the crosshead link and both pieces of the combination lever, disconnecting the main-valve rod and compression-valve rod, of course, and tie their ends up to clear the lower arm of the bell crank; block both valves at the centre of their travel, and proceed on one side.
Q. 10.—How could you adapt the valve gear to a working condition when the crosshead link should be broken?
A.-It would be well worth while to be prepared with a remedy for this accident, for otherwise the engine would be disabled on the one side; this woulu necessitate reducing the train load, if the engine already had its full rated tonnage; and reducing the train load on account of disability of the locomotive is one of the definitions of engine failure on most roads.
Remove all pieces of the crosshead link; and if a rod or lever can be obtained which, with one end fastened to the guide yoke and the other end fastened to the lower end of the combination lever, will hold the combination lever in a vertical position—that is, with the pin hole in the lower end of the lever on a plumb perpendicular line through the centre of the rocker, or bell-crank shaft—you can go right on with your train; some power is lost, of course, through the suppression of the lap-and-lead motion regularly received from the crosshead; but the valve will have its “long travel” from the motion of the eccentric, and in full gear will take the train right along.
If the combination lever can not be so secured, its lower end should be swung over to within ten or twelve inches of the guide yoke and fastened there by wire or stout cords, the main-valve rod and the compressionvalve rod disconnected from the combination lever and tied up out of the way, and the valves centred and clamped as usual in such disconnections; then proceed, under the power of the other side of the engine.
Q. 11.-If the radius bar fails, what should be done?
A.-Remove the broken pieces of the radius bar; block the bell crank with the vertical arm in a plumb perpendicular position, by blocking through or lashing the bell-crank arms to the gear frame. The front end of the eccentric rod will now be supported by the transmission bars. Proceed, with the valves receiving the lap-and-lead motion as has been previously explained.
THE BAKER-PILLIOD VALVE GEAR
This highly efficient valve motion combines the main features of the Walschaert gear with the principle of Marshall's modification of the Hackworth gear, and certain original and clever movements that overcome most of the objectionable features found in the valve motions heretofore used on locomotives. The motion work is all outside the engine frame where it is easy of inspection, lubrication, and repair; the latter in particular, as all points of motion transmission are fitted with hardened pins and bushes, and lost motion due to wear is at a minimum; and there are no expensive "links" in this gear—it is simply an ingenious system of levers, with no eccentric sheaves and straps nor sliding blocks.
The manufacturers have recently introduced an im
proved design of the Baker-Pilliod valve gear, and which will be referred to in detail; but as most of the locomotives so far equipped have the original style of the gear, the latter will be described first. Referring to Fig. 48 in which the gear is arranged for outside admission, an eccentric crank A is attached to the main pin as in the Walschaert gear, and the forward end of the cccentric rod is connected with the transmission bar at pin C. The combination lever E is in the form cf a bell crank which is supported at its upper end by a fixed fulcrum, and through which the forth-and-back motion received from the crosshead is transformed into an up-and-down motion, delivered to pin C through the link D; pin C therefore travels in a circular path, as shown in the cut, due to the forward-and-back impulse of the eccentric rod and the raising and-lowering effect of link D. The motion of the eccentric rod is therefore always in parallel, as both ends describe uniformly almost the same circular paths.
What apparently is a lever, Y, is really a yoke rocking on the fixed fulcrum, K; the reverse bar connects with this yoke at S, and the position of the yoke is fixed by the position of the reverse lever, pin H at the upper end of the yoke moving through the arc as shown. From pin H the radius bar G depends, pin P at its lower extremity carrying the forward end of the transmission bar R. The transmission bar has only three