Q. How is the cylinder-casing held on? A. It is best held out from the cylinder-walls by the flanges on the cylinder ends, and held on these by the front and back covers being slipped over it. Q. How is the danger of knocking out a cylinder-head, by water carried over from the boiler or left by condensation, lessened? A. By cocks at each cylinder end, controlled from the cab, and by which the cylinders may be bled from time to time if the engines work water or after starting. (See Figs. 134 and 135.) Fig. 135. Combination Cylinder-cock and By-pass Valve, Q. From what part should the cylinder be lined? A. From the counterbore, which is never worn out of size or shape. But it must first be scraped clean of oil crust, etc. Q. What kind of a line should be used? A. As fine as possible. Q. If the back head is up, how is the back end of the cylinder to be lined? A. By the stuffing-box. Q. What is the cause of cylinder condensation? A. The cylinder wall, which at admission has a lower temperature than that of the entering steam, condenses part of this latter, unless it is superheated, when it merely lowers its temperature without actual condensation. Q. What influence has the thickness of the cylinder on the amount of temperature reduction? A. The thicker the wall, the less this reduction; as the mass of iron acts somewhat as a reservoir of heat. Q. What influence has relative cylinder diameter? A. In so-called "square" engines there is more wall for a given volume than in those with stroke longer than the diameter. Q. What disadvantage have cylinders of large diameter? A. They have excessive cooling and frictional surface; further, their steam ports are seldom proportionately large. Q. What has been the usual fault of American locomotive design? A. Excessive cylinder capacity for the boiler, and for the weight of the drivers. Most American engines are able to slip their drivers, which shows unnecessary cylinder power. Thus where diameter and stroke are each 10 inches, the head area is 78.54 X 2 157.08 square inches; the convex surface 31.416 × 10 10314.16 square inches; total surface, 471.24 square inches; volume, 78.54 X 10 = 785.4 cubic inches; ratio of surface to volume, 1 to 1.67. With 10 inches diameter and 15 inches stroke the head area is 157.08 square inches, convex surface 471.24 square inches, total surface 628.32 square inches, volume 1,178.1 cubic inches; ratio of surface to volume, 1 to 1.88. With 10 inches diameter and 20 inches stroke we have the same head area as with 10 inches X 10 inches, but double the convex surface; hence total surface of 785.4 square inches, double the volume 1,570.8 cubic inches; ratio of surface to volume, 1 to 2. Q. What precaution is taken to lessen the loss of heat and lowering of pressure due to internal condensation by reason of radiation from steam-chest and cylinder walls? A. They are lagged with a non-conducting substance, as wooden strips, and usually have an air-jacket or double wall; the cylinder-heads are in the same way double. Sometimes, instead of wooden strips, hair felt is used as a non-conductor. Q. What are the results of tests as regards steam jacketing of compound locomotives? A. According to Borodin, without steam in the jackets the economy of steam was 13 per cent, of fuel 24 per cent, over non-compounds, but with steam in the jackets. there is increased consumption of both steam and fuel. CHAPTER XLV THE STEAM-CHEST Q. In what position are the steam-chests? A. In the American engines, on top (see Fig. 1); in British engines, or at least on those which have inside cylinders, on the sides next the center line of the machine. Q. What are the advantages of top chests? A. The engine is kept within less width than if they were on the side. Q. What are the disadvantages? A. The cylinder is more difficult to free from water than if the valve was on the side or beneath. Q. What are the advantages of having the valve-chest and slide-valves on the cylinder side, as in English insideconnected engines? A. The cylinders are more readily drained of water. Q. Where is the valve-chamber of the Vauclain engine? A. In the cylinder-saddle, as shown, between the boiler and the cylinders. (Figs. 126 and 127.) Q. How are the steam-chests for flat D-valves made? A. They usually consist of rectangular frames forming chests or boxes without either top or bottom, fastened to the cylinder-casting by a steam-tight joint, and having a cast-iron cover of considerable strength to resist the internal steam-pressure on its flat surface. Q. How are the valve-seats made? A. They are planed as true as the planer will make them, then filed and scraped until smooth and practically plane. Q. What name is given to the plate covering the top of the steam-chest? A. The steam-chest cap, as distinguished from the casing above it. Q. What name is given to the other casing on top of the steam-chest? A. The steam-chest cover, as distinguished from the cap which it covers. Q. What is the disadvantage of the usual system of having the steam passages alongside of the exhaustpassages from the chest of the cylinder? A. That the exhaust cools the live steam, unless there is considerable compression; also there is danger of cracking the saddle by unequal temperatures. Q. Describe the "Universal" valve chest. A. This is a piston-valve arrangement for application to existing slide valve seats, saving the old valve-cylinders and frame ends. It is shown in Fig. 136, as adapted to either inside or outside admission. There is a supporting inner valve chamber jointed to the valve seat independent of the outer chest, that is seated on the cylinder apron in the usual way, thus utilizing the regular inlet port to the chest. Q. What is its principal object? A. To facilitate superheating by providing extra free |