636 



HYDRAULICS AND ITS APPLICATIONS 



Where the conditions are very variable, however, the guide or diffuser 

 ring may easily prove an actual source of loss by shock rather than of 

 efficiency. Under such circumstances the guides are preferably omitted, 

 the most suitable type of pump being one fitted with a moderate vortex 

 chamber and volute, this both on account of its greater adaptability to 

 varying circumstances, and of its cheaper construction. 



TYPES OF CKNTRIFUGAL PUMP. 



Centrifugal pumps may be divided into three classes : 

 (1) Pumps having a single impeller with open vanes, and discharging 

 directly into a volute casing or vortex chamber. 



FIG. 305. Open Vaned Centrifugal Pump with Balancing Vanes. 



(2) Pumps having a single impeller with encased vanes, and either dig 

 charging as above, or fitted with a diffuser ring between impeller and 

 vortex chamber. 



(3) Compound pumps, which are invariably fitted with encased vanes and 

 with diffuser rings with or without the addition of a vortex chamber. 



Fig. 305 shows an example of the first type, having an axial inlet on one 

 side only of the impeller. Here the water is deflected into a radial direction 

 by the conical disc on which the vanes are formed. 



