762 



THE COMPLETE GRAZIER. 



wheel is replaced by a turbine. A double discharge turbine, as a rule, 

 has to be completely submerged below the standing tail water level 

 before it will work efficiently, hence a deep pit must be excavated when 

 the turbine is a fairly large one, and every foot of depth greatly increases 

 the risk of coming across springs or causing trouble with the neighbour- 

 ing foundation. This question of foundations should always be con- 

 sidered in comparing prices of turbines. Provided the turbine has a 

 good head of water above it, there is no difficulty in making the platform 

 upon which it is placed, several feet above the tail water level, where 

 it is a convenience so to do, the additional fall being used by means of 

 an extension of the draft tube or suction pipe. Another advantage of 



Fig. 328. Gilkes & Co.'s Double Vortex Turbine. 



this type is that when the head water is shut off at the sluices the 

 turbine is left dry on its floor, and can thus be readily inspected. 



In the case of the Double Vortex the water enters the outside casing 

 at the top or in any other position that may be convenient and pass- 

 ing thence is directed by four (or more) guide blades on to the outer 

 circumference of the revolving wheel, which is driven round at a velocity 

 depending on the height of the fall. The water, having expended its 

 energy in giving motion to the wheel, is discharged through the two 

 central openings, half the amount being carried away by each suction 

 pipe. The guide blades are movable, and turn about on a pivot placed 

 near their inner ends. In any application of water power, there are 

 certain losses of effect which are unavoidable ; but in the Vortex, by 

 various improved arrangements and adaptations, their amount is 



