In principle the Steam Turbine is a machine for directly converting into rotary motion a portion of the kinetic energy of steam. There are two principal types of turbines : one, in which nearly the whole available energy of steam is used in an expanding nozzle to give to itself a very high velocity, before being utilised in giving rotary motion to a wheel; the other, in which the steam passes alternately through many rings of fixed guide blades and of revolving blades, and expands by a small

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... unt during its passage through each ring, until it leaves the last row and is discharged into exhaust, having parted with the greater portion of its usable energy. The De Laval Turbine is of the first order, the Parsons of the second. The Rateau and the Curtis Turbines combine some of the features of both. All these turbines may be either of the parallel or of the radial flow type, but have mostly been developed on the former lines. The velocity attained by steam in the Parsons Turbine, compared with that in the De Laval Turbine, is low, as it depends on the small difference of pressure on the two sides of a ring of blades, and, as this pressure difference can be made very small, depending, as it does, on the number of rows of blades, it is possible to reduce the velocity of the steam, and therefore the speed of rotation of the wheel, to very manageable limits. The Parsons Modern Steam Turbine is shown in section in Fig. 1 . It consists primarily of the casing C, which carries the stationary guide blades S, and the rotor or spindle R, which carries the moving blades M. The rotor is carried by two main bearings B, B" which are the only portions of the turbine proper subject to mechanical friction. Fig. 2 shows the type of bearing used in the smaller turbines up to about 500 k.w. output. It is formed of a solid gun-metal bush B, in which the spindle of the rotor revolves. The bush is made with a solid collar at one end and a loose collar at the other. Between these collars and surrounding the bush are three tubes, T, Ti, T2. Small clearances are allowed between the outside of the bush and the inside of the first tube and betw'een the outside and inside surfaces of the tubes themselves. These small clearance spaces are arranged so that oil can be forced into them. A flexible bearing is thus obtained, which allows the rotating mass to take up its natural centre line of revolution, and the viscous friction of the oil in the clearance spaces helps to damp any vibration set up by small inaccuracies in balance. The lug L prevents the bush turning with the spindle.