Steam Turbines / A Book of Instruction for the Adjustment and Operation of the Principal Types of this Class of Prime Movers

by Hubert E. Collins

Special Turbine Features to be Inquired into

Before leaving the prime mover itself, and proceeding to the auxiliary plant inspection, it may be well to instance a few special features relating to the general conduct of a turbine, which it is the duty of a tester to inquire into. There are certain specified qualifications which a machine must hold when running under its commercial conditions, among these being lack of vibration of both turbine and machinery driven, be it generator or fan, the satisfactory running of auxiliary turbine parts directly driven from the turbine spindle, minimum friction between the driving mediums, such as worm-wheels, pumps, fans, etc., slight irregularities of construction, often resulting in heated parts and excessive friction and wear, and must therefore be detected and righted before the final test. Furthermore, those features of design—and they are not infrequent in many machines of recent development—which, in practice, do not fulfil theoretical expectations, must be re-designed upon lines of practical consistency. The experienced tester's opinion is often at this point invaluable. To illustrate the foregoing, Figs. [66], [67], and [68] are given, representing, respectively, three distinct phases in the evolution of a turbine part, namely, the coupling. Briefly, an ordinary coupling connecting a driving and a driven shaft becomes obstinate when the two separate spindles which it connects are not truly alined. The desire of turbine manufacturers has consequently been to design a flexible coupling, capable of accommodating a certain want of alinement between the two spindles without in any way affecting the smooth running of the whole unit.

FIG. 66

Fig. [67]

In Fig. [66] A is the turbine spindle end and B the generator spindle end, which it is required to drive. It will be seen from the cross-sectional end view that both spindle ends are squared, the coupling C, with a square hole running through it, fitting accurately over both spindle ends as shown. Obviously the fit between the coupling and spindle in this case must be close, otherwise considerable wear would take place; and equally obvious is the fact than any want of alinement between the two spindles A and B will be accompanied by a severe strain upon the coupling, and incidentally by many other troubles of operation of which this inability of the coupling to accommodate itself to a little want of alinement is the inherent cause.

Looking at the coupling illustrated in Fig. [67], it will be seen that something here is much better adapted to dealing with troubles of alinement. The turbine and generator spindles A and B, respectively, are coned at the ends, and upon these tapered portions are shrunk circular heads C and D having teeth upon their outer circumferences. Made in halves, and fitting over the heads, is a sleeve-piece, with teeth cut into its inner bored face. The teeth of the heads and sleeve are proportioned correctly to withstand, without strain, the greatest pressure liable to be thrown upon them. There is practically no play between the teeth, but there exists a small annular clearance between the periphery of the heads and the inside bore of the sleeve, which allows a slight lack of alinement to exist between the two spindles, without any strain whatever being felt by the coupling sleeve E. The nuts F and G prevent any lateral movement of the coupling heads C and D. For all practical requirements this type of coupling is satisfactory, as the clearances allowed between sliding sleeve and coupling heads can always be made sufficient to accommodate a considerable want of alinement, far beyond anything which is likely to occur in actual practice. Perhaps the only feature against it is its lack of simplicity of construction and corresponding costliness.

FIG. 68

The type illustrated in Fig. [68] is a distinct advance upon either of the two previous examples, because, theoretically at least, it is capable of successfully accommodating almost any amount of spindle movement. The turbine and generator spindle ends, A and B, have toothed heads C and D shrunk upon them, the heads being secured by the nuts E and F. The teeth in this case are cut in the enlarged ends as shown. A sleeve G, made in halves, fits over the heads, and the teeth cut in each half engage with those of their respective heads. All the teeth and teeth faces are cut radially, and a little side play is allowed.