650 



HYDRAULICS AND ITS APPLICATIONS 



And since the initial tangential velocity of the water, before coming under 

 the influence of the impeller is zero, this becomes 



W W Q 



U - iv a r a w = - - w>s 



y 9 



toot IDS. per second. 



U 3 



foot Ibs. per Ib. 



This is quite independent of all losses in eddy formation, shock, and 

 friction in the wheel passages, and if to it be added the work done against 

 the friction of the impeller on the surrounding water, against the 

 mechanical friction of the bearings, and that absorbed in pumping water 

 which may leak from the discharge side to the suction side of the impeller, 



the result will give the power required 

 to drive the pump. The work done 

 against these resistances may be ex- 

 perimentally obtained by driving the 

 pump at the required speed of rotation 

 with the discharge valve closed so as 

 not to deliver any water, and by noting 

 the power then absorbed. This will, 

 however, be somewhat high owing to 

 the fact that leakage round the im- 

 peller will be greater than under 

 normal running conditions, and also 

 that power will be absorbed, owing, to 

 the viscosity of the water, in main- 

 taining a rotation of the water in the 



eye of the pump and in the collecting chamber surrounding the wheel. 

 Also, in all probability, in maintaining such a series of currents as 

 indicated in Fig. 322. 



Energy obtained from Pump. The useful work done by a pump is the 

 product of the weight of water handled and the height through which 

 this would be lifted provided there were no losses of head in suction an< 

 delivery pipes. 



If // is the difference of level between suction and discharge reservoi 

 ll f the friction loss in suction and delivery pipes, and v the velocity 

 flow along the discharge pipe, the energy obtained from the pump per Ib. 



FIG. 322. 



; 1 1 v > 



ich 



, 



of water = II 



H f + - foot Ibs. 

 f 9 



If pressure gauge or manometer readings be taken on the suction and 

 delivery pipes at the same level immediately before and behind the pump 



