CHAP. VIII. 



TURBINES. 



'03 



materially less than in turbines of some varieties. The power is ob- 

 tained with a slower velocity of the water than in ordinary turbines. 

 This is effected by a peculiar balancing of the centrifugal force of the 

 water in the revolving wheel against the pressure due to half the head, 

 so that only one-half of the fall or head is employed in giving velocity 

 to the water, the other half acting simply in the condition of fluid 

 pressure. Hence the velocity of the water in no part of its course 

 exceeds that due to one-half of the fall, and the loss from fluid friction 

 and agitation of the water is thus materially less than in other turbines 

 where the water is required to act at much higher velocities. 



Although high falls are uncommon on agricultural estates or farms, 

 there is a demand in some cases for a simple and efficient water motor 



Fig. 329. Gilkes & Co.'s Pelton Wheel for High Falls. 



suited for such falls. The high speed of inward ilow turbines under 

 great heads of water being unsuitable for conveniently disposing of the 

 power, the need has arisen for a turbine wheel the diameter of which 

 may be increased without diminishing the efficiency. The Pelton wheel, 

 which is a development on scientific lines of the " Miners' " or " Hurdy- 

 Gurdy" wheel, meets the above-mentioned requirements admirably. 

 The water impinges from a nozzle on to a number of bifurcated bucket:; 

 fastened round the periphery of a pulley. These buckets can be fixed, 

 and the nozzles changed to suit requirements, by any intelligent labourer. 

 Notwithstanding the simplicity of the machine it is essential that great 

 attention should be paid to proportion in design, and to the workmanship, 

 if the best efficiency is to be obtained. 



