240 



THE IRRIGATION AGE. 



power factor of the motor to be used. Roughly, in 

 small units, a transformer capacity of 1.2 kilowatts is 

 required for each horse power actually delivered by the 

 motor, but as the capacity required varies in accord- 

 ance with the method of connecting the transformers, 

 ihe advice of a competent engineer should be secured 

 before making a decision. 



COSTS OF IRRIGATING. 



The costs of pumping an acre-foot of water (45,360 

 cubic feet) to any height with electricity depends only 

 upon the cost of the current, without regard to the 

 time required, the capacity of the pump, or the power 

 of the motor, provided only it is assumed that the effi- 

 ciecies of the units of various sizes are the same. Since 

 this is true with but a small variation, it is considered 

 a fact in compiling the annexed table. In this table 

 the costs of pumping an acre-foot of water to various 

 heights are given at various costs of electricity, with 

 corrections for small pumps, belted units, etc. In order 

 to determine the total cost of pumping for the season, 

 the monthly charge for readiness-to-serve (if any) must 

 be added to the figures taken from the table. For 

 example, suppose we have a 20-horse power motor-pump 

 lifting water 30 feet high, including pipe friction, and 

 are irrigating 200 acres of land, the pump capacity 

 being 1,600 gallons per minute, and cost of current 50 

 cents per month per horsepower for readiness-to-serve, 

 plus 31/2 cents per kilowatt-hour. According to the 

 table, we find the cost of an acre-foot of water lifted 30 

 feet, with current at 3% cents, is $1.76. If we want 

 one acre-foot per acre we will want 200 times this, or 

 $352. For a 20-horse power motor, the monthly charge 

 will be $10, or $50 for the five irrigating months. 

 Total costs for the year will then be $402, or $2.01 

 per acre. If, instead of one acre-foot, or 12 inches' 

 depth over all the land, we used 8 inches' depth, the 

 cost of current would be two-thirds of $352, or $234.65, 

 plus $50, or $284.65, equal to $1.42 per acre for the 

 200 acres. 



for each acre of land, find out how many gallons per 

 minute pump capacity you have for each acre, and 

 divide that into 5,400. In the above case, we have 

 1,600 gallons per minute for 200 acres, or 8 gallons 

 per minute per acre. Divided 5,400 by 8 and the 

 result 675 is the number of hours required. 



KILOWATT-HOURS REQUIRED. 



A kilowatt of current will do a little more than 

 a horse power of work, and a kilowatt of power run- 

 ning for one hour is called a kilowatt-hour. In the 

 case of the 20-horse power motor-pump described above, 

 the actual requirement of power at 70 per cent pump 

 efficiency is 17 horse power. A little less than, 17 

 kilowatts of electricity are required to operate the 

 motor about 15 kilowatt, to be precise and the motor 

 would consume 15 kilowatt-hours of current per hour. 

 During the season the pump was to operate 675 hours, 

 requiring a total of about 10,125 kilowatt-hours, which 

 at y/2. cents, amount to $354.35, making a fair check of 

 the figures given in the table. 



Cost of pumping per acre of land lying at various heights at various 

 costs of electricity in cents per kilowatt-hour. The quantity of water 

 delivered will be one acre-foot or a depth of 12 inches. 



TOTAL HEAD IN FEET, INCLUDING FRICTION. 



These costs are based upon horizontal centrifugal pumps, direct 

 connected to motors, with efficiencies as follows: 



Pump 68% 



Motor 88 % 



Pump and motor 60% 



If pump capacity is under 900 gallons per minute, make additions 

 as follows: 



700 gallons per minute 10% 



500 gallons per minute 20% 



300 gallons per minute 30% 



Under 300 gallons per minute 40% 



Figures for 5 and 10 feet may be a little low unless pumps are of 

 large capacity. 



Costs for higher heads are in proportion. For instance, costs for 

 95 feet equal costs for 45 plus 50 feet. 



For belted units add 5 per cent. 



A good horizontal centrifugal pump with capacity of 900 gallons or 

 more per minute will give 68 per cent efficiency, but if a pump of poor 

 efficiency is used, an addition must be made to the costs. 



If a vertical pump is used add from 5 per cent to 100 per cent in 

 accordance with type of pump, style of setting and method' of carrying 

 or balancing the downward thrust of the shaft and runner. 



THE IRRIGATION AGE is preparing to publish all of 



State Armory, where the Seventeenth^tional Irrigation Congress will hold its Mr R ey b o l<3' s articles in book form. This WOrk Will not 



be issued until the full series of fifteen or more articles 



LENGTH OF TIME TO PUMP. 



In order to determine the number of hours that 

 a pilmp must operate to give one acre-foot of water 



is published in this journal. This book will be fully 

 illustrated, cloth bound, and will retail for $2.00, post 

 paid. 



