488 TwijNTY-EiGiiTH Annual Report 



tory, for which electric current from the central power plant of the 

 University is available. The engines are all of the four-cycle type, 

 and it may be added that the Experiment Station strongly recom- 

 mends that type in preference to two-cycle hot-ball engines*. 



This department has designed also a new water supply system 

 for the University campus during the past year. The new system 

 is unique and its main features should go on record at this time. 

 The pump room is situated in a l^asement 74 feet ])y 24 feet. At 

 one end is a reinforced concrete sump of 48,000 gallons capacity, 

 into which the discharge from the well is delivered. The pressure 

 jfumps are in duplicate, of 100 gallons per minute capacity, and 

 start automatically when the water pressure drops to 26 and 23 

 pounds per square inch. When the pressure reaches 33 pounds, 

 the pumps stop automatically. The discharge line is connected 

 with a 5,000-gallon pneumatic pressure tank which is kept about 

 two-thirds full of compressed air. Floor space is reserved for 

 another pressure tank to be added later, and the remaining space 

 is for fire service pumps. The new system is giving good service, 

 with better pressure than was had formerly with the elevated tank. 



EXTENSION WORK 



For two months during the height of the pumping season in 

 1917, this department kept one of its assistants in the field assisting 

 farmers with refractory engines and pumps, and helping them to 

 secure better fuel economy. The Casa Grande Valley and the 

 McAllister and Whitewater districts were covered in this way. 



The irrigation engineer devoted two weeks in June, 1917, to lec- 

 turing in Navajo and Apache counties. Ten lectures were delivered. 

 During this trip and throughout the year assistance has been given 

 to farmers and canal companies on irrigation and other farm en- 

 gineering subjects. 



GRADING LAND FOR IRRIGATION 



Considerable study has been given to the subject of preparing 

 land for irrigation, particularly land on relatively heavy slopes as 

 from 25 to 100 feet per mile. The principal agricultural valley 

 lands in Arizona lie at slopes of 8 to 15 feet per mile, and these, 

 lands can be irrigated very efficiently. On lands that take water 



* Vide Bui. 74, Ariz. Agr. Exp. Sta., pp. 429-433. 



