WIXDMILLS AND PUMPS. 251 



lass. A small iron crank at one end of the windlass 

 operates the pump. 



Pumps. There are four distinct types of pumps, 

 the pluiiLivr or piston pump, which includes the wind- 

 mill, steam and many devices of power pumps; the 

 vacuum, the rotary, and the centrifugal, besides elevators 

 which raise water by means of flights attached to an'end- 

 less 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 designed especially 

 for handling clear water grit, sand and foreign mate- 

 rial 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 essential that the working parts of these pumps 

 should fit closely, there is necessarily great friction and 

 corresponding 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 

 friction 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, cen- 

 trifugal pumps are recognized by all hydraulic engineers 

 as the most efficient and durable, the cheapest and best. 

 The vacuum pump is an entirely different principle, hav- 

 ing no movable parts, except a small automatic shifting 

 bar in the yoke, to operate the valves. These pumps are 

 made with a pair of cylinders working alternately as the 

 atmospheric pressure is removed from them, thus allow- 

 ing the water to rtish in and discharge itself. They are 

 useful only for small lifts, and theoretically are not calcu- 



