All About Engines

Steam Turbines 171 in black near the left-hand of the drum. In order to provide room for the gradually expanding steam, both the diameter of the drum and the length of the blades increases as the exhaust is approached. The thrust bearing, b, to prevent the shaft from moving endwise, will be seen on the extreme left. At each end of the shaft is an arrangement, c, for preventing the escape of steam from the casing. These consist of grooves, on the shaft into which project thin strips of brass, while exhaust steam from the governor serves as a “ packing.” Dummy pistons, D, constructed much in the same way, and with steam acting upon them in such a way as to oppose the endwise push on the blades, serve to “ balance ” the thrust, so that the thrust bearing itself is mainly a safeguard. Above the first two sets of blades will be seen a passage, e, through which steam can act on these dummies. The governor and the method of driving it will be readily understood from the section. It does not operate the throttle valve directly, but admits or prevents the admission of steam for this purpose. The valve is never quite still, and a little steam is always being used to operate it. It is this steam which is used for “ packing ” the glands. There is also an emergency governor which acts in a way not very different from that described on page 161. It only comes into action when the speed exceeds the normal by 10 or 15 per cent. The blades in the first few rows are of copper, because that metal resists most satisfactorily the