CENTRIFUGAL PUMPS 



637 



Fig. 301 shows a pump having vanes open on both sides, with a suction 

 inlet on each side of the wheel. This type has the advantage of being 

 perfectly in balance as regards axial thrust on the shaft, while the single 

 inlet type necessitates provision being made for balancing any such thrust. 

 On the other hand, the single inlet pump is particularly convenient for 

 situations where a vertical shaft is permissible, and, as denoted in the 

 figure, lends itself to a very compact and simple type of construction. 



.a b. 



FIG. 306. Single and Double Inlet Encased Impellers with Vortex Chamber and Volute. 



The open vane pump is, however, subject to considerable and incalculable 

 loss by slip or leakage of water between the pump casing and impeller 

 blades, and while this may be reduced by making the clearance at these 

 points as small as possible, the presence of gritty matter in suspension in 

 the water causes rapid wear, and the slip may then become excessive. 

 Furthermore, the disc friction accompanying the rotation of such open 

 vanes over the surface of the casing is considerably greater than when 

 the vanes are enclosed at the sides by discs or shroudings, so that on 

 every count the latter encased type of pump is preferable. Such a pump, 

 Fig. 306 a and b, may have either single or double suction inlet, and 



