494 CONSTRUCTION, FARM ENGINEERING, MECHANICS 



Barometric pressure at different altitudes, as affecting pumps 

 With equivalent head of water and the vertical suction lift of pumps 



Windmill Figures 

 Windmills for pumping (Rayner). 



Windmills vary in type and efficiency from a four-arm direct-con- 

 nected paddle wheel, erected on a single post, to the modern curved 

 blade, back-geared, steel windmill, erected on a scientifically con- 

 structed steel tower. 



To select a proper-sized windmill for the purpose required, the speed 

 of the wind in the particular locality should be considered. In the 

 United States, this information can be readily secured from the nearest 

 weather bureau station. When the average speed is above eight 

 miles per hour, throughout the year, the following table may be fol- 

 lowed safely : 



LIFT (ft.) 



8-ft. diameter windmill . 3 -inch diameter pump, 40 



8-ft. diameter windmill 2^-inch diameter pump, 70 



10-ft. diameter windmill 3 -inch diameter pump, 70 



10-ft. diameter windmill 2J^-inch diameter pump, 120 



12-ft. diameter windmill 3 -inch diameter pump, 100 



2^-inch diameter pump, 180 



, 2 J^ -inch diameter pump, 200 



2 -inch diameter pump, 300 



12-ft. diameter windmill 

 12-ft. diameter windmill 

 12-ft. diameter windmill 



When the average speed of the wind is less than given above, a pro- 

 portionally larger diameter windmill should be chosen. 



In the lift that is required of the pump, the elevation above the 

 ground to the top of the elevated tank or cistern should be added to 

 the depth of the well. 



