GUIDE VANES 



635 



guide vanes around the impeller, as shown in Fig. 304, 1 having angles so 

 designed as to receive the water without shock on leaving the wheel, and to 

 direct this by gradually diverging passages, either into a vortex chamber, 

 or directly into the collecting volute from which it is taken by the dis- 

 charge pipe. In the latter case the pressure change takes place entirely 

 in the guide passages themselves. The angle a which the guide vanes make 

 with the circumference of the discharge circle is calculated exactly as in the 

 case of the inlet vanes of a turbine, and, where the pump is required to 



FIG. 304. 



work under variable conditions, should be suited to the discharge at which 

 the maximum efficiency is desired. Thus fitted, the pump becomes in 

 every essential a reversed turbine, and is commonly known as a " turbine " 

 pump. Where the guides deliver into a vortex chamber they should be 

 designed so as to follow the curvature of the stream lines in free vortex 

 flow with the discharge, and with the tangential velocity at the entrance 

 to the guides, obtaining under normal conditions of woridng. The ring 

 of guide vanes in such a pump is known as the diffuser ring. Under 

 favourable circumstances such an arrangement is capable of converting 

 up to 75 per cent, of the kinetic energy at discharge into pressure energy. 



1 By courtesy of the Buffalo Steam Pump Company. 



