473 



HYDRAULICS AND ITS APPLICATIONS 



twice this, and its width being about four times that of the wheel. By this 

 means, part of the kinetic energy of the discharge is converted into pres- 

 sure energy, and since the pressure at the outside of the diffuser is that 

 corresponding to the depth of immersion, the pressure at the inside and 

 at the exit from the turbine wheel is less than this, so that the effective 

 head is increased. In this manner the efficiency may be increased by 

 about 6 per cent, in a well-designed turbine under moderate head, the 

 proportional increase being less as the head increases. The device is, 

 however, now practically obsolete. 



The outward flow turbine suffers in efficiency from the fact that its 

 passages are of necessity divergent and that flow through these diverging 

 passages is always accompanied by loss of energy in eddy production. 

 It is, moreover, an expensive machine, not easy to govern well, and has 



FIG. 222. Outward Eadial Flow Turbine with Diffuser. 



been generally replaced by turbines of the Francis or some other more 

 modern type. 



The following results of tests on a Fourneyron turbine fitted with an 

 internal cylinder gate, are given by Unwin, 



first series of turbines the ring gates are arranged to open downwards, the idea being that it 

 is safer to allow the gates to open suddenly in case of accident to the coupling rods than to 

 close suddenly, because of the probable effect of water ram in the latter case. The fact that 

 the lower section of both wheels is not opened for the escape of water except at full load, and 

 the possibility of a dangerous accumulation of detritus taking place in these sections, along 

 with the nuisance caused by the violent upward escape of water against the turbine deck, led 

 to the gates in the second series of turbines being designed to shut downwards. The gates 

 are regulated by a mechanical relay governor having the gearing, which moves the gates, 

 operated by clutches put in motion by changes of speed, the motion of the governor balls 

 allowing one or another pa\vl to gear with a ratchet wheel, which gives motion through the 

 clutche- and gearing to a rack coupled to a lever on the lay shaft from which the gates are 

 directly worked. 



A counterbalance veight is used to balance the weight of the gates and coupling rods. 



While these turbines have given satisfactory results, the whole of the later series of 5,000 j 

 H.P. and 10,000 H.P. turbines are of the inward radial flow type. 



