WINDMII.LS AND PUMPS. 369 



Pumps. — There are four distin(5l types of pumps — . 

 the plunger or piston pump, which includes the wind- 

 mill, steam, and many devices of power pumps ; the 

 vacuum, the rotary, and the centrifugal, besides ele- 

 vators which raise water by means of flights attached 

 to an endless chain. The plunger pump, of necessity, 

 moves the water more slowly, as it only travels at the 

 speed of the piston. The plunger pump also is de- 

 signed especially for handling clear water — grit, sand, 

 and foreign material cut the pistons and barrel of the 

 pump. While these pumps will move the water 

 slowly, they will move it a long distance, or against 

 heavy pressure when properly designed. The pumps 

 of next greatest capacity are the rotary pumps. Of 

 these there are many designs. They handle water 

 much faster than do plunger pumps, but as it is essen- 

 tial that the working parts of these pumps should fit 

 closely, there is necessarily great fri(5lion and corre- 

 sponding loss of efficiency, and hence they are short- 

 lived, especially when pumping water that is muddy 

 or gritty. The pumps of greatest utility for low lifts 

 are the centrifugal pumps. These are built with no 

 close-fitting parts and no valves ; consequently there is 

 no fridlion on the parts of the machinery, and they are 

 not affected by sand, mud, or gritty water. Hence, 

 for irrigation, where the lift does not exceed fifty feet, 

 centrifugal pumps are recognized by all hydraulic en- 

 gineers as the most efficient and durable, the cheapest 

 and best. The vacuum pump is an entirely different 

 principle, having no movable parts, except a small 

 automatic shifting-bar in the yoke to operate the 

 valves, These pumps are made with a pair of cylin- 



