REGULATION OF TURBINES 515 



If specially designed for the particular head, flow, and speed of rotation, 

 this class of wheel is well adapted for moderate powers and for medium 

 heads up to about 35 feet where the head is fairly constant, and where 

 part-gate efficiency is unimportant as compared with low first cost. The 

 general practice of manufacturing it in stock sizes, and of supplying that 

 size which most nearly meets the requirements of the purchaser instead 

 of designing the machine to suit its location, together with the fact that 

 such American machinery has in the past been characterized by a 

 flimsiness of construction unusual in English and Continental practice, 

 has, however, had the effect of discrediting this class of turbine simong 

 European engineers to an extent greater than its inherent disadvantages 

 deserve. Evolution in this type of machine would appear to be tending 

 in the direction of fewer and deeper buckets with wider openings to avoid 

 obstruction. 



ART. 139. GOVERNING OF TURBINE PLANTS. 



The difficulties in the way of the efficient speed regulation of a water 

 wheel or turbine are many and peculiar to this form of motor, and the 

 problem is much more complicated than in the case of a steam engine or 

 turbine. In either type of motor, when running at a uniform speed there 

 is an exact balance between the energy given up by the motive fluid pel- 

 unit time in its passage through the motor and the energy absorbed in 

 useful work and in overcoming friction. If more load is thrown on, in 

 either case the speed diminishes until the work done against the increased 

 resistance is again equal to the energy given up by the fluid. 



In the case of a steam engine or turbine, directly the speed diminishes 

 the governor alters the admission valves, admits more steam to the 

 cylinders, and in a very short interval of time an exact balance is again 

 set up between the supply of and the demand for energy, so that the 

 engine again runs at a uniform, though slightly lower, speed. The 

 admission valves being light and easily moved, the governor itself is in 

 general quite capable of adjusting these rapidly and accurately, while, 

 since the steam is an elastic fluid and in a state of high compression, any 

 slight opening of the valves is accompanied by an instantaneous rush of 

 steam at high velocity. 



Also, since the amount of available energy per pound of high pressure 

 steam is very great, the mass and inertia of the column of motive fluid are 

 comparatively small, so that its velocity may be rapidly changed without 

 any appreciable change in the pressure in the steam chest. Thus, in an 

 efficiently governed steam engine, fitted with a flywheel of fair size, it is 



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