All About Engines

How a Modern Engine Works 5 round the toothed sector d by means of the rod e, and the sector causes a toothed wheel on the axle of the pointer to rotate. The pointer then indicates on the dial the pressure of steam in the boiler. There is one other safety contrivance fitted to all boilers which must be noticed now, and that is the water-gauge. If any part of the interior of the boiler upon which the hot gases play is not in contact with water it may become overheated. The metal is then injured, or at any rate buckling occurs, and stresses are produced which the structed to bear. Consequently, the water must be maintained above a certain level. On the other hand, it must not be too high, or some passes over with the steam, and as water is not elastic, in the sense that steam is, it is of no use in driving the engine. The water- gauge shown in Fig. 4 is a glass tube, communicating with the interior of the boiler above and below the proper water level, and the level of the water in boiler was not con- Fig. 4.—Water-gauge in part section the tube shows the level of the water in the boiler. When this gets too low more water is pumped in. THE ENGINE We can now consider a simple engine, learn its parts, and examine its mode of operation.