496 HYDRAULICS AND ITS APPLICATIONS 



Where an ample water supply is available this falling off in efficiency is 

 unimportant, and as this turbine admits of a simple and fairly cheap 

 construction, and is capable of close speed regulation, it often forms the 

 most suitable type tc use. Where, however, high part-gate efficiency is 

 more important than low first cost, one form or other of the turbine 

 invented by Professor James Thomson becomes advisable. 



ART. 136. THE THOMSON VORTEX TURBINE (FiG. 235). 1 



The special features of this turbine, which is an inward radial flow 

 machine, consists in the form of chamber in which the runner is mounted, 

 called the vortex chamber, and in the type of guide vane adopted. The 

 runner, which is similar to that of the Francis turbine, is mounted inside 

 a spiral casing. Water enters tangentially at the largest part of the spiral 

 (as shown in Fig. 236), and sweeps around the casing, the area of which 

 is so arranged that the linear velocity of the supply water is the same at 

 all points of the circumference. A common, but less correct type of con- 

 struction, is that indicated in Figs. 235 and 237, in which the water enters 

 the casing radially and divides into two streams flowing along either side 

 of the wheel. In either case the entering water is directed into the wheel 

 buckets by a series of guide vanes placed around the outer circumference, 

 these being designed so as to follow the lines of flow in a spiral vortex. 

 These guides vary in number from four to eight and are movable, being 

 pivoted near their inner ends, so as to be approximately in balance. They 

 are coupled together by a series of bell-crank levers and links as indi- 

 cated in Fig. 236, 2 so as to rotate together and shut off water equally from 

 all parts of the wheel. Motion is given to these guide vanes either by 

 hand or by an automatic governor. Where the load and the supply head 

 are constant the guide blades may be fixed, the ports then being j 

 designed so as to give the full-power flow. This gives a much cheaper j 

 machine, and where a battery of turbines is in use, it is in general prefer- 

 able to give fixed blades to all but one or two, regulation for small load / 

 variations being performed by those machines having movable guides, j 

 and for large variations by cutting out one or more of the machines with 

 fixed guides. 



1 By courtesy of Messrs. G. Gilkes k Co., Ltd., Kendal. 



2 By courtesy of the plat-t Iron Works, Dayton, Ohio. 



