1 66 T/ie Drainage of Fens and Low Lands. 



1ABLE X. 



To find the horse-power required for j^ti7nping-*engiiies, 



H.P. = 33,000 lb. (14*73 tons) lifted i foot higli per minute. 



N.H.P. — ^The nominal horse-power of an engine is a commercial 

 term, used solely for the purpose of giving a general 

 idea of the power of an engine. 

 I.H.P. — The indicated horse-power is the power of the engine 

 calculated from the mean pressure of the steam in the 

 cylinder throughout the whole of the stroke, as 

 obtained by indicator diagrams. 



W.H.P. — The horse-power in water actually raised and discharged. 

 Efficiency. — The efficiency of pumping machinery is expressed by 

 the percentage of useful effect in water raised of the 

 power given off by the engine, as found by the 

 indicator diagram. Thus, if the indicated horse-power 

 is represented by 100, and 40 per cent, of this is 

 absorbed in working the engine and pump, the 

 efficiency of the machinery is 60 per cent., or adopt- 

 ing the decimal notation and taking perfection at 100, 

 the efficiency would be * 60. The difference depends 

 on the efficiency of the machinery; the best engines 

 and centrifugal pumps give off as much as 60 per cent, 

 of the indicated horse-power. Although the trials do 

 not record the proportion of this due to the engine as 

 separate from the other part of the machinery, of the 

 difference, approximately 10 per cent, may be given to 

 the engine, and 30 per cent, to the pump. In ordinary 

 practice it would not be safe to reckon on a higher 

 efficiency than 60 per cent, for the pump, or 50 

 per cent, for engine and pump. 



To find the net horse-power (W.H.P.) required to lift any given 

 quantity of water a given height per minute : — 



1. Multiply the number of cubic feet of water by 62 * 5, and by the 



height in feet which it has to be lifted, and divide the product 

 by 33,000; 



2. Or, multiply the number of cubic feet of water by the height to 



be lifted in feet, and divide by 528 ; 



3. Or, multiply the number of cubic feet by '0019 ('00189393, &c.), 



and by the height to be hfted in feet. This gives a slight 

 excess. 



