676 



HYDRAULICS AND ITS APPLICATIONS 



shrouding equalises the pressure in the interior of the balance ring 

 and of the impeller. 



This is then approximately in balance, the 

 slight reduction in the diameter of the balance 

 ring creating an excess pressure towards the 

 inlet, which counterbalances the change of axial 

 momentum of the supply water. 



Brass packing rings are fitted at P (306A) to 

 prevent leakage of pressure water from the 

 clearance space into the balance ring. 



A somewhat analogous method of balancing a 

 single impeller is shown in Fig. 328. 



Where a centrifugal pump is fitted with a 

 vertical shaft, the whole weigjit of the pump 

 and driving shaft may usually be balanced by 

 an application of the preceding principles ; while 

 exactly the same reasoning applies to the balanc- 



iag of the axial thrust on a turbine shaft. 

 FIG. 328. 



ART. 184. EXAMPLES OF THE DESIGN OF CENTRIFUGAL PUMPS. 



As an example of the application of the foregoing formulae, the main 

 points in the theoretical design of one or two types of pump will now 

 be considered. 



(1) Low-lift pump 12 feet working head to deliver 6,000 gallons per 

 minute at 220 revolutions. 



= x/12 = 6-95 f .B. 



Then 



__ 

 3 " fa "62-4 X 6-95 



= 31-5 f.s. 

 = 2*31 square feet. 

 = 332 square inches. 



while 



2 TT x 220 

 A* 332 



= 1-367 feet = 16'4 inches. 

 = 3-22 inches. 



2 TT 7-3 ~ 2 TT x 16-4 



?' 2'25 

 Assuming a ratio = r-, this makes r a = 7'3 inches, and if the vane 



