Drainage by Steam Power. 65 



the increased capacity of the pump and wheel. The wages 

 of the night men for the short time they are required will not 

 be found to amount to as much in a large pumping station 

 as the annual payment of interest and repayment of capital 

 on the extra cost of the engines and drains required to run 

 for only a limited time. 



In calculating the work to be done, the height which the 

 water is lifted is taken as the vertical distance between the 

 surface of the water in the drain bringing the water to the 

 pump, and that in the main drain or river into which it is 

 discharged. If the water is discharged through horizontal 

 pipes — as in one form of the centrifugal pump — an allowance 

 has to be made for the friction. Consideration must be given 

 to the fact that this height may vary considerably in the 

 course of the day, owing to the outfall being a tidal stream, 

 or from the water having lowered in the feeding drain during 

 the time pumping is in operation. 



If the pump used is of the turbine form, its position in the 

 pump well should be sufficiently below the lowest surface to 

 which the water is to be pumped to prevent its drawing air, 

 as within reasonable limits the depth of the pump below the 

 surface does not add appreciably to the work to be done. 

 The covering over the pump should not be less than 2 feet 

 If the main interior drains are of sufficient capacity the in- 

 clination in the surface of the water should not exceed 3 inches 

 per mile, and even 2 inches are sufficient to bring the water to 

 the pump. The surface of the water in the drains for effectual 

 drainage should be at a sufficient distance below the land to 

 allow the drain pipes to discharge freely from the lands situ- 

 ated at the greatest distance from the pumps. In alluvial 

 soils this will be from 3 feet to 3 feet 6 inches, and this, plus 

 the amount to be allowed for the surface inclination from 

 the furthest point, will regulate the level at which the water 

 should be kept in the main drain. 



The main drains leading to the engine, and especially the 



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