The Golden State: Where & How to Live, Secure, Visit, Enjoy and Thrive in California
Sprinkler Irrigation
The nearest size electric motor is 15 hp. If a water cooled gas engine or diesel engine is to be used, multi- ply 14 x 1.45 = 20.3 BH.P, being sure that the engine selected will produce 20 BH.P continuously.
If an air cooled engine is to be used, multiply 14 x 1.6—22.1 BH.P, being sure that this engine has a continuous rating of at least 22 BH.P. You will then get longer life and usually much more efficiency. To estimate fuel consumption of gasoline engines a thumb rule can be used for fair accuracy. Most engines will use a pint of gasoline per horsepower per hour.
When engines arc used at high elevations, some power is lost due to the thinner air. 3% per 1000' of elevation is lost starting at 3000'. Below 3000' no deduction is necessary.
Pressure Loss
We have said that we should keep the pressure loss between the first and last sprinkler on a lateral to within 20 percent of the starting pressure; however, there are conditions where a 20 percent loss would be too great. For instance, a low pressure system losing 20 percent of its starting pressure would not be able to efficiently operate the last sprinkler. Also, at a 20 percent loss a lateral operating up to 12 hours between moves, would have considerable more water deposited at the first sprinkler than at the last; therefore, use a lateral size that will not exceed a 10 percent pressure loss on systems operating on 20 pound pressure or less and on systems that operate more than six hours between moves. On all other systems allow up to a 20 percent loss.
Uniform Precipitation
The amount of water delivered per sprinkler depends directly upon the nozzle pressure. As the sprinkler discharge controls the precipitation rate, it is necessary to maintain a fairly uniform pressure in order to obtain even precipitation. In order to maintain a uniform pressure, where more than one lateral is operated, it is necessary to install a pressure gauge between the riser valve and the first sprinkler on each lateral line. Then the valve can be adjusted until the gauge reads the required operating pressure. Otherwise put the gauge on the pump discharge and regulate the engine for a single line operation.
Types Of Sprinkler Systems
We have discussed in this handbook only one type of sprinkler irrigation system; the permanent or portable main with portable laterals. This system is the one most extensively used, and, since the basis for design is essentially the same for all types, information on the use of this system may be applied to others.
