60 BULLETIN 462, U. S. DEPARTMENT OP AGRICULTURE. 



capacity equivalent to about 1 inch of rainfall per week for the 

 entire area when the plant is running 5 to 8 hours per day. 



Two general types of pumps are used in irrgation — high-pressure 

 and low-pressure. The former are used in Florida for such plants 

 as those using the high pressure overhead-spray systems and for 

 many of the hose systems. The low-pressure systems, as a rule, are 

 not used for exerting pressure over 20 to 30 pounds per square inch, 

 but are employed extensively for irrigation purposes throughout the 

 West and are the best design of pump for most surface methods as 

 used in Florida. 



The designs of pumps are innumerable, but two general types, the 

 centrifugal and the displacement pumps, are most adaptable to 

 Florida conditions. The centrifugal pump consists of a circular 

 shell which incloses a swiftly rotating impeller. The water enters at 

 the center of this impeller and is forced by the velocity imparted to 

 the water by the curved fans of the impeller out of a discharge pipe 

 leading from the outer edge of the shell. In Florida these pumps 

 are used in the one-stage (having one impeller) and two-stage (hav- 

 ing two impellers) types. The single-stage pump is built in sizes to 

 lift any quantity of water to 75 to 125 feet. The two-stage pump 

 will lift twice as high as a single stage. The single-stage pump is 

 used for low-pressure work on surface systems and some spray sys- 

 tems of irrigation. The two-stage pump is used on several spray 

 systems where the total head exceeds 75 feet. 



Centrifugal pumps are, in general, most adaptable for pumping 

 large quantities of water with the smallest installation cost. The 

 efficiencies range from 30 to 65 per cent. They are built in many 

 different forms to fit different water supplies, including wells. They 

 are light in weight, require small space, seldom need repairing, have 

 no valves, and are injured but little by grit in the water. These 

 pumps should be placed as close to the water as possible and never 

 exceed a suction lift of 25 feet. All air must be expelled from the 

 pump case and suction pipe and these must be filled with water be- 

 fore starting. The speed must be proportional to the lift and quan- 

 tity of water to be pumped. 



Low-pressure centrifugal pumps range in cost from 1 cent to 

 5 cents per gallon per minute capacity. High-pressure pumps range 

 from 5 cents to $1.25 per gallon per minute capacity. The smaller 

 the pump the higher the rate of cost per unit of capacity. 



Displacement pumps lift water by means of a close-fitting plunger 

 or piston traveling backward and forward in a cylinder equipped 

 with valved openings. The best known displacement pump in 

 Florida is the small, single-acting piston type used for domestic pur- 

 poses, commonly called the pitcher pump, and usually operated by 



