422 Bulletin 92 



Semi-diesel engines burn lower grades of fuel, the grade called 

 "27-plus" being well adapted to that type. The outlook for an abun- 

 dant supply of that grade of oil, however, is not encouraging, and the 

 cost is not much lower than that of gas oil, not enough lower to ofifset 

 the greater cost of the engines and of attendance. 



Diesel engines are not built in small units. Large diesel engines 

 are preeminent for central power plants, and central plants have been 

 advised strongly for pump irrigation districts. Fuel oil for diesel 

 engines costs five-ninths as much as gas oil and the consumption per 

 unit of power is only one-half as much, but the losses in generator, 

 transformers, transmission line, and motors aggregate about one-third 

 of the power generated, and the additional investment in high-priced 

 engines, electrical equipment, and transmission line is so high that the 

 power economy of the central plant system is partly nullified. The 

 convenience and ease of operation of motor-driven pumps is an im- 

 portant argument for the central power plant, but the experience in 

 Arizona has been that the power goes off the line frequently, some- 

 times several times a day, and many transformers have been burned 

 out during the summer rainy (and electrical) season. From the stand- 

 point of fuel conservation and the public's interest therein, the diesel 

 engine central plants should be built wherever the irrigated district is 

 large enough to require 400 horsepower and is fairly compact in area. 



For central plants, steam power cannot compete with diesel en- 

 gines. Engines of the Hvid or Brons type have not been tested l)y 

 the writer as to fuel economy and reliability, and no judgment can be 

 expressed. It is hopefl to investigate this type of engine in the near 

 future. 



Another possibility of great promise is that of hydro-electric 

 power. Good water-power projects are not situated in close proximity 

 to the pumping districts of southern Arizona. The Sabino Canyon 

 project is the only one in Pima County that is known to be feasible. 

 There is no pl■o^•ed water-power project in Cochise County or Yuma 

 County. Tn central and northern Arizona there is much imdevelopcd 

 water power. Power will be developed in connection with the San 

 Carlos project, and one or two additional power plants can be built 

 in the Gila Canyon when the flow of water becomes equalized. Much 

 more development is possible on the Salt and \^erde rivers. In the 

 Grand Canyon of Arizona there is almost unlimited latent water power : 

 the length of a transmission line necessary to reach the Casa Grande- 



