FOURNEYRON TURBINE 



477 



The second method, by incrc asing the pressure at exit, diminishes the 

 effective head and increases 

 the loss of kinetic energy at 

 exit, and is hence very ineffi- 

 cient at part gate. In the first 

 turbines erected at Niagara 

 Falls, which were of the Four- 

 neyron type, and of 5, 500 H. P., 

 this method of governing was 

 adopted with satisfactory 

 results as regards speed regula- 

 tion. 1 



Outward flow turbines are in 

 general difficult to govern, 

 because an increase in speed 

 caused by a reduction in load 

 increases the centrifugal pres- V Turbine Wheel 



Sure of the water in the turbine FIG. 220. Section of Multiple Chamber Fourneyrori 

 wheel, and thus causes an in- Turbine Runner and Guides, with Inside Cylinder 



creased outward flow which 



tends to increase the speed still further. Governing by throttling the 



discharge has the advantage that it does to 

 some extent tend to counterbalance this 

 action. 



The fact that centrifugal force tends to 

 increase the velocity of flow through the 

 wheel also explains to some extent why 

 the speed of the wheel is of necessity so 

 high under high heads. 



The efficiency of the Fourneyron turbine 

 may be increased by the addition of the 

 diffuser, probably invented by Boyden 

 (1844). 



This consists of a xed annular casing 

 (Fig. 222), surrounding the wheel and 

 fitting closely to the outer periphery of the 

 moving vanes. The sides of this casing 

 diverge gradually, its depth increasing from that of the buckets to about 



1 These turbines were designed by Messrs. Faesch and Piccard (1895), and work under 

 132 feet head. A full load efficiency of 82-5 per cent, is said to have been obtained. In this 



Runner 



FIG. 221. Outside Cylinder Gate. 



