Many of the portable systems use gun sprinklers. Some growers are willing to trade off the higher energy costs for the savings in labor costs. There are some gun sprinklers that will operate satisfactorily at lower pressures and some growers are using these, but they have reduced radius of coverage and, therefore, higher application rates, assuming equal flow rates. There are some low pressure impact sprinklers that have been marketed for the last several years. They also have reduced radius of coverage and this may increase the application rate.
Flow is the rate water is being delivered to the sprinklers.
After computing TDH, a pump efficiency should be assumed so that horsepower can be computed using the above formula. Pumping Plant Performance Evaluation , for a discussion of recommended pump efficiencies to select. If proper design guidelines are used and sprinklers are operated at the manufacturers' recommended mid-range of operating pressures, these systems should be reasonably energy efficient. Pump selection should include the use of high efficiency pumps and matched power units. Unfortunately, some of the older systems have sprinklers, pumps, and power units that are 20 or more years old and need replacing.