« НазадПродовжити »
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 of 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 connections-pins C, L, and P; ignoring pin L for the moment, it will be perceived that the circular motion of the back end of the transmission bar at pin C will produce a pendulum-like swing of radius bar G; if the reverse lever is placed in forward gear, drawing the reverse bar to the left, yoke Y will be inclined at an angle with pin H to the left of its position as shown in the cut; then, as a forward motion is imparted to the transmission bar, the lower end of radius bar G will swing to the right with a rising motion, swinging back on the return to the left with a fall; if the reverse lever should be placed in back gear, inclining yoke Y to the right, a forward movement of the transmission bar will cause pin P of the radius bar to swing to the right with a downward motion, and with a rising one on its return swing to the left; now note that any up or down movement of connection P means a corresponding up or down deflection of the forward portion of the transmission bar R.
Another bell crank is fulcrumed by the pin T, and its lower arm is connected with the valve rod by pin Q; link M connects its upper arm at pin N with the transmission bar at pin L. It should be plain, now, that a rising movement of the forward portion of the transmission bar will drive the valve forward, and a falling movement will pull the valve backward, and that the forward-and-back travel of the valve is secured from the up-and-down glide of pin P when yoke Y is inclined at an angle with the vertical; and to reverse the engine, it is only necessary to reverse the direction of inclination of yoke Y; or to shorten the cut-off, to raise the yoke toward the mid position as it is shown in the cut.
As to the necessary advance of the valve to equal the lap and lead: with the engine standing as in Fig. 48, it will be observed that the eccentric is at its extreme backward position, and if the reverse lever should be placed in full gear-either forward or back—the valve would occupy the position of its farthest traverse, either front or back, that would not be affected by combination lever E at all during the reversion, for there is a straight line of motion at this time from eccentric to pin L; also, if the crosshead link should be disconnected and combination lever E rigidly secured in the vertical position shown in the cut, as the wheels revolved the eccentric would give a motion to the valve scarcely affected by the connection at pin C, which would merely act as a swinging support to the eccentric rod and transmission bar. The motion received from the crosshead affects the valve, then, only when the piston and main pin are at the beginning of a stroke; the eccentric and pin C are then at the upper or lower middle of their paths of revolution, and with radius bar G paralleling the yoke Y, the valve would be in