The Harrisburg Tandent-Conyound Engine.—The Ide tandem-compound engine, as manu factured by the Foundry and Machine Department, at Harrisburg, Pa., is shown in Fig. 41.
The extra heavy shaft and fly-wheel are supported between the bearings, avoiding the over hang of the fly-whgel, as is the case in the center-crank type. One of the special features in the Harrisburg tandem compound is the method of connecting the high and low pressure cylinders. It admits of moving the low-pressure cylinder head into the connections to exam ine the low-pressure cylinder and piston without removing the high-pressure cylinder or its steam and exhaust connections. The inability to do this has been one of the greatest objec tions to the tandem-compound engines as usually built. The manner of supporting the high pressure cylinder is more substantial than the general practice, avoiding the vibration of cylin ders when working under full load.
The ideal Engine, made also by the same builders, is shown in Figs. 49 and 43. It is a single-cylinder automatic engine, with the peculiar feature of being self-lubricating. The sectional view shows the principle of the automatic oiling device.
The Sioux City Corliss Engine, of the tandem compound class. is shown in perspective in Fig. 44. Fig. 45 is a half-section of the cylinder, showing that the steam is taken between (not river) the valves, and that. the exhaust-chamber is cast separate and independent from the cylinder, thereby' preventing a cold, wet steam-jacket. The steam-valves are all made so as to relieve themselves in case of water. Fig. 40 shows the hook-motion valve-gear, Fig. 47 the dash, and Fig. 48 the governor, which has light balls made to run at three times the speed of the engine, and a heavy sliding weight.
The sectional view of the cylinder of this engine is shown in Fig. 49, and a side view of the valve-motion is shown in Fig. 50. eite's releasing valve-gear, as applied to this engine, is shown in the accompanying detailed cuts.
Fig. 51 is a front elevation, and Fig. 52 is a plan. These show the valve-gear as it appears when engaged, and in the middle of its travel. Figs. 53, 54. and 55 are rear elevations. Fig. 53 shows the parts in engagement at the moment the valve begins to open ; Fig. 54 shows the posi tion of the parts immediately after the valve has been released, and Fig. 55 illustrates the action of the stop-motion.
In all the figures A represents the valve-stem and B the valve lever, which is secured to the end of the valve-stem by a feather and set-screw. C C' is a double crank, which vibrates loosely on a sleeve around the valve stem, and is connected by an adjustable link-rod to the wrist-plate. from which it receives its motion. The end of the arm C carries a small rock-shaft D, which has a hook .E fastened on one end. This hook is provided with a hardened steel catch-plate b, which engages a similar plate c fastened on the end of the valve-lever B, and the hook is kept in place by a light spring f. On the end of the rock-shaft D, opposite the hook E, is fixed a forked crank F having a pin h on which is mounted a sliding-block s, and the outside of block a is fitted to move in a slot i of a link O. The link is mounted at and vibrates about a point/ in one arm
of a bell-crank II, and the crank oscillates upon a sleeve around the valve-stein. The other arm of the bell-crank II is connected by an adjustable rod z to the governor. By re ferring to Fig. 53, in which the double crank C C' is moved by the wrist-plate in the direction indicated by the arrow, and fol lowing the motion of the inner end of the block s, and also of the inner end of the slot i, it will be seen that these points will come together when the curved dotted lines 2 and 3 cross each other, and as the movement continues the block s will be pushed farther from the center of the valve-stem, and when the center line of the link shall be coincident with radial line 1, as shown in Fig. 54, the block will have been pushed so far outward that it will have slightly turned the small roek-shaft D, and moved the hook E enough to release the valve-lever B. Then the dash-pot will act and close the valve. At this moment of release, effected by the toggle-like action of the link, the pressure on the bell-crank _II, caused by the liberation, will be exerted in a radial line from the cen ter of the slot through the point/ to the center of the valve-stem or the stand which supports it, and during the entire movement of the hook E there will be no appreciable strain to turn the bell-crank II, and consequently there will be no strain to disturb the normal action of the governor. As the position of the bell-crank His controlled by the governor, any change in the height of the governor will cause a change in the position of the point j, and a correspond ing change in the time of release. The action of the automatic safety-stop motion is illus trated by Figs. 53 and 55. Fig. 53 shows the position of the various parts when the engine is at its lowest normal speed, and the hook E is at the point of engagement with the valve lever B. The lower side of the link G is provided with an adjustable embossment w, which, in the position shown, is just clear from the hub of the bell-crank H. Now, should the governor belt be broken, or if from any other cause the governor-balls should fall below this point, the bell-crank 11 will be moved in the direction indicated by the arrow in Fig. 55, the emboss ment we will be brought against the hub of the bell crank, and the continued movement of the bell-crank will cause the embossment to act as a fnlet•unr, and the lower side of the slot i will cause the pill h in the forked crank F to move outward, or from the center of valve-stem A. This will carry the hook outward so far that it will not engage with the valvedever and the valve will remain closed. In connection with the above, an attachment is placed on the governor eohunn, by miens of which the :lethal of the stop-mo tion may be suspended or made operative at any I hue by the engineer, and when suspended the engine can be slopped and started in the usual way.