JONVAL TURBINE 



479 



ART. 133. THE JONVAL TURBINE. 



By shortening the casing of the Borda turbine, and adding suitable guide 

 vanes to direct the water under pressure into the wheel, Jonval (1843) 

 devised a form of turbine 

 which had many advan- 

 tages over and largely dis- 

 placed the Fourneyron 

 turbines then in use. In 

 this, which is an axial flow 

 turbine, water is directed 

 by means of radial guides 

 into a series of radial buc- 

 kets (Fig. 223). Since 

 each particle of water in 

 its motion through the 

 wheel remains at approxi- 

 mately the same distance 

 from the axis, the effect of 

 centrifugal force on the 

 flow becomes negligi- 

 ble, and the difficulty in 

 governing which is so pro- 

 nounced in the Fourney- 

 ron turbine is thus re- 

 moved. 



In all axial flow tur- 

 bines, however, whether 

 of the pressure or impulse 

 type, the linear velocity of points at the entrance to the buckets varies 

 with the radius, and as the velocity of efflux from the guide passages is 

 approximately uniform, there is, with radial vanes, only one particular 

 radius at which the ratio between the velocities of the wheel and of 

 efflux is suited to any given blade angles. For efficient working, and to 



FIG. 223. Jonval Turbine. 



