STEAM ENGINE. 



389 



the machinery to be driven by the engine in motion. 

 There is a cast iroi) frame m m m, upon which the 

 cylinder and most of the other fixed parts of the 

 engine are bolted. The two rods n n, n n, which 

 guide the cross head, are made fast at their ends to 

 the framing of the engine, so that the axis of the pis- 

 ton rod may always be in a line with the axis of the 

 cylinder. The frame mm m, is fixed down by means 

 of bolts to the bottom of the building shown under 

 the engine. A small pump o o, is wrought by the 

 cross head: its use is to supply the boiler with 



water. A pipe is joined to the branch p to carry 

 the water into the boiler, and a pipe from the 

 branch q passes into a well. The cylinder has a 

 cover fixed upon both ends, each cover being accur- 

 ately fitted and made steam tight. 



By inspecting fig. 4, it will be seen that each end 

 of the cylinder has a communication with the cast 

 iron chest or box r, by means of a passage which 

 runs nearly over one half of the length of the top 

 side of the cylinder, passing into the cylinder at one 

 end and into the chest at the other. There is 



4. 



another passage or space besides the passages just 

 mentioned, which also opens into the chest r; this 

 space does not communicate with the inside of the 

 cylinder, but communicates with the pipe s, which 

 is called the eduction or escape steam pipe. There 

 is another pipe, t, seen in both figs., which admits 

 steam from the boiler. The steam chest r, together 

 with the other parts described in this paragraph, 

 constitute the nozles. 



Inside of the chest r, a small box is shown, with 

 its open side undermost, and covering the passage 

 which leads into the end, y, of the cylinder, as also 

 the middle space or eduction port. This last 

 described box is called the slide valve. The valve 

 is made steam tight to the surface upon which it 

 works, by first planing the parts in contact, and 

 afterwards grinding the one part upon the other. 



In the position of the valve, as shown in the 

 drawing, no steam can escape from the boiler into 

 the end y of the cylinder, but there is a communi- 



cation with the boiler and the end a of the cylinder, 

 and as the side of the valve next the hollow is 

 above the passage leading into the end y of the 

 cylinder, and also above the eduction opening or open 

 port, if there then be any steam in the end y of 

 the cylinder, it has a free escape into the atmosphere, 

 through the pipe s. If the valve was pushed end 

 ways, so that its hollow side were above the passage 

 leading to the end a of the cylinder, and also above 

 the space which lies between the passages into the 

 cylinder, then there would be a communication 

 with the end a of the cylinder and the atmosphere, 

 and also a communication with the boiler and the 

 end y of the cylinder. When the crank shaft 

 revolves, the valve is kept working from its position 

 in the drawing to the position just described, and 

 back again to the position shown in the sketch, 

 once during each revolution of the shaft by means 

 of a wheel u, fixed upon the crank, called the eccen- 

 tric wheel, in such a manner that the axis of the 



