Centrifiigal Pumps. i o i 



speeded. The formulas for ascertaining the quantity of water 

 discharged by a centrifugal pump are complicated, and the 

 coefficients vary with each particular make. Messrs. Easton 

 and Anderson furnish the purchasers of their drainage pumps 

 with a diagram by which the quantity discharged can be 

 ascertained by inspection when the lift and speed are known. 

 If an account is kept of the lift, and the speed and time of 

 working of the engines by the engine-driver, checked by 

 locked counters attached to the machinery giving the number 

 of revolutions, a means is provided of preserving a record of 

 the quantity of water pumped, and at the same time a check 

 is placed on the engine-driver. 



In the centrifugal, as in all other pumps, a certain amount 

 of the power applied in driving them is absorbed by friction 

 of the bearings and resistance due to roughness of the surface 

 of the pump, and to the slip and eddying motion of the 

 water ; this loss varies from 30 to 50 per cent. The duty to 

 be expected from a centrifugal pump of the best construction 

 used for drainage purposes may be taken at about 70 per 

 cent, falling in small-sized pumps, and those not of the best 

 construction to 50 per cent. The power absorbed by an 

 engine and pump may be divided approximately as 

 follows : — 



Friction of engines 10 per cent 



pumps 30 



Efficiency 60 „ 



100 



The ratio of useful effect in water lifted, as compared with 

 the indicated horse-power, for the direct-acting engines and 

 pumps put up by Messrs. J. and H. Gwynne, has been found 

 to vary from 55 to 70 per cent 



The efficiency of a centrifugal pump rapidly diminishes if 

 the lift is greatly increased. From observations made by 

 Mr. Richards of the pumps used for lifting water for irrigating 



