LOCOMOTIVE ENGINE. 429 



fig. 14, before its motion is changed and it begins to move back again; this dis- 

 tance that the slide moves beyond the port is called the travel. The waste port 

 is always covered by the slide, as the travel is less than the width of the bars, 

 so that the steam is always prevented from entering the waste port from the 

 steam chest. During the reciprocating motion of the slide, each of the steam 

 ports is alternately uncovered, and the steam allowed to enter and flow into the 

 cylinder ; the port is than covered again by the slide, and when the flanch has 

 passed over, communicates through the inside of the slide with the waste steam 

 port, allowing the steam which has performed its duty in the cylinder to escape 

 by the port at which it had entered, into the waste port and out at the blast pipe ; 

 this action is called the eduction. The slide valve is held upon the face of the 

 ports only by the pressure of the steam upon it, which is quite sufficient to keep it 

 always steam-tight whilst moving; as all the inside of the slide is open to the air 

 through the waste port, and the flanches fit air-tight upon the face of the ports, so 

 that the whole pressure of the steam upon the slide is effective in keeping it down ; 

 the area of the slide being 55 square inches, the pressure upon it is about 

 l-if tons. In large stationary engines the steam is admitted under the slides, as 

 the pressure of the steam upon the slides would be more than is necessary to keep 

 them tight, and would cause very great friction ; the slides have, in this case, to be 

 held down by other means, as packing or springs upon the back of them. At the 

 extreme position of the slide, as in fig. 14, the inner edge of the flanch G ap- 

 proaches the opposite bar, thus contracting the opening of the waste port to the 

 size of the port out of which the steam is escaping ; if contracted more, the free 

 exit of the steam would be obstructed. 



The front end of each of the cylinders is closed by a cast iron cover W, seven 

 eighths of an inch thick, let into it; the cylinder runs through the plate of the smoke 

 box, projecting beyond it, and having a flanch resting against the inside of the plate, 

 and fixed to it by bolts, which are screwed through the plate into the flanch. The 

 cylinder cover W is of the same size as this flanch, and is held on to the cylinder 

 by the same bolts that fix the cylinder to the smoke box plate ; the heads of the 

 bolts are made thin to clear the cover, and the bolts are prolonged beyond their 

 head to pass through the cover, and have nuts screwed upon them on the 

 outside. The other end of the cylinder has also a flanch, by which it is bolted to the 

 inside of the tube plate; this is shewn on a larger -scale in figs. 15 and 16, 

 which are a longitudinal and a cross section of the cylinder to a scale of 2 inches 

 to a foot, or three times the engravings. is a section of the cylinder; P P 

 the back steam port leading into the end of the cylinder ; Q Q is the tube plate 

 or back plate of the smoke box; and R the flanch upon the cylinder, similar to that 

 at the other end. The cylinder runs through the plate, and comes flush with 



