A well designed sprinkler system applies water uniformly to the soil surface, and is capable of applying enough water to meet the peak demands of the crop without producing excess runoff. Good design considers such factors as pressure nozzle size and spacing, wind, air temperature and humidity (day versus night), soil intake rate, crop rooting depth and water use.
The flow rates from a sprinkler nozzle depend upon nozzle size and water pressure. Flow rates for selected nozzle sizes and pressure are given in table 1. Typical sprinkler flow rates may vary from 4gpm from a 5/32 inch nozzle at 30 pounds pressure to over 11gpm from a 7/32-inch nozzle at 70 pounds pressure. The nozzle sizes are usually stamped on the side of the nozzle. Wheel move systems typically have 3/16-inch nozzles.
On sloping fields there may be considerable pressure differences between sprinkler heads on high and low ends of the line. In this situation flow control nozzles may be used to improve the uniformity of water application. Flow control nozzles apply water at nearly the same rate when operated within the rated pressure range of the nozzles.
Precipitation Rate (how hard is it raining)
The precipitation Rate (Pr) is the rate at which water is delivered from the nozzle, averaged as inches per hour, over the area covered by one nozzle. It is important to consider the Pr when designing a sprinkler system, since water will run off if applied faster than the soil can absorb it. Precipitation rates can be calculated using the following formula.
Pr (inches/hr) = 96.3 x nozzle flow rate (gpm) / area covered (ft)
The flow rates from a sprinkler nozzle depend upon nozzle size and water pressure. Flow rates for selected nozzle sizes and pressure are given in table 1. Typical sprinkler flow rates may vary from 4gpm from a 5/32 inch nozzle at 30 pounds pressure to over 11gpm from a 7/32-inch nozzle at 70 pounds pressure. The nozzle sizes are usually stamped on the side of the nozzle. Wheel move systems typically have 3/16-inch nozzles.
On sloping fields there may be considerable pressure differences between sprinkler heads on high and low ends of the line. In this situation flow control nozzles may be used to improve the uniformity of water application. Flow control nozzles apply water at nearly the same rate when operated within the rated pressure range of the nozzles.
Precipitation Rate (how hard is it raining)
The precipitation Rate (Pr) is the rate at which water is delivered from the nozzle, averaged as inches per hour, over the area covered by one nozzle. It is important to consider the Pr when designing a sprinkler system, since water will run off if applied faster than the soil can absorb it. Precipitation rates can be calculated using the following formula.
Pr (inches/hr) = 96.3 x nozzle flow rate (gpm) / area covered (ft)
Note: flow rates are for agricultural sprinkler heads with brass nozzles. Sprinkler nozzle flow rate is proportional to the square root of the water pressure at the base of the nozzle thus doubling the pressure does not double the flow rate.
Precipitation rate can be calculated as follows:
In a typical wheel move system, each sprinkle covers 2400 square feet. This is based on a spacing of 40 feet between sprinklers on the line, and a 60 foot move
(40’ x 60’ =2400 square feet). With 3/16 inch nozzles that are operating at 50 pounds pressure, the nozzle flow rate is 7.0 gpm (from table 1.) the precipitation rate would be.
Pr = 96.3 (7.0gpm)/2400 ft = 0.28 inches per hour.
Application Rate (how much of the rain stays in the soil)
The application rate (Ar) is the average rate at which water is stored in the soil, in inches per hour.
Ar = Application Efficiency (Ea) x Precipitation rate (Pr)
Typical sprinkler application efficiency values vary from 60% to 80% with 70% a reasonable average.
Precipitation rate can be calculated as follows:
In a typical wheel move system, each sprinkle covers 2400 square feet. This is based on a spacing of 40 feet between sprinklers on the line, and a 60 foot move
(40’ x 60’ =2400 square feet). With 3/16 inch nozzles that are operating at 50 pounds pressure, the nozzle flow rate is 7.0 gpm (from table 1.) the precipitation rate would be.
Pr = 96.3 (7.0gpm)/2400 ft = 0.28 inches per hour.
Application Rate (how much of the rain stays in the soil)
The application rate (Ar) is the average rate at which water is stored in the soil, in inches per hour.
Ar = Application Efficiency (Ea) x Precipitation rate (Pr)
Typical sprinkler application efficiency values vary from 60% to 80% with 70% a reasonable average.
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