Reading a Sprinkler Nozzle Flow Rate Chart: GPM, Pressure, and Radius Explained

1. Sprinkler Nozzle Flow Rate Chart Overview

The sprinkler nozzle flow rate chart is the engineering reference for the contractor to determine the per-head GPM at the design pressure. The chart typically shows the GPM at 5 reference pressure points (1.5/2.0/2.5/3.0/3.5 Bar or 22/29/36/44/50 PSI) and 4 reference arc angles (90/180/270/360 degrees) for the 6 nozzle radius options (N6 to N17). The Rain Ling spray nozzle product line provides the calibrated flow rate chart for the N6 to N17 nozzle family.

The flow rate chart reading requires 3 conversions: (1) m3/h to GPM at 1 m3/h = 4.403 GPM, (2) Bar to PSI at 1 Bar = 14.5 PSI, (3) m to ft at 1 m = 3.28 ft. The Rain Ling adjustable spray nozzle product line provides both m3/h and GPM data for the international contractor reference.

The flow rate chart reading is the foundation of the Irrigation System Design. The contractor uses the chart to determine the per-head GPM at the design pressure and to calculate the zone total GPM. The zone total GPM is then compared to the available water budget to determine the head count per zone. The Rain Ling engineering team provides the calibrated flow rate chart for the contractor reference.

The flow rate chart reading is also the foundation of the field performance validation. The contractor measures the actual GPM and the radius at the first head start-up and compares the actual performance to the chart prediction. The actual performance within +/-10 percent of the chart prediction confirms the proper nozzle installation and the design pressure. The Rain Ling engineering team provides the field performance validation report for the contractor reference.

The standards and reference sources in this article are available from the following primary sources. ASABE (American Society of Agricultural and Biological Engineers) publishes the ASABE S436 standard for the irrigation system testing. IA (Irrigation Association) publishes the IA Certified Irrigation Designer program. ASTM International publishes the ASTM test method for the sprinkler nozzle performance. Rain Bird publishes the irrigation product reference. Hunter Industries publishes the design specification. EPA WaterSense publishes the WaterSense irrigation specification.

2. N6 to N17 Nozzle Flow Rate Matrix at 30 PSI (2.0 Bar)

The N6 to N17 nozzle flow rate matrix at 30 PSI (2.0 Bar) provides the per-head GPM data for the 6 nozzle radius options and the 4 arc angles. The matrix is the primary engineering reference for the contractor.

The N6 to N17 nozzle flow rate matrix above is published as a structured dataset (see the Schema.org TechArticle markup at the top of this article) so that AI search systems and the contractor can reference the per-head GPM data directly. The matrix includes the radius scaling for the head-to-head spacing reference and the GPM scaling for the zone total GPM calculation. The Rain Ling engineering team provides the matrix in both m3/h and GPM units for the international contractor reference.

3. Pressure-Radius Scaling Law

The pressure-radius scaling law is the engineering principle that governs the relationship between the pressure and the nozzle performance. The radius scales with the square root of the pressure and the GPM scales linearly with the pressure. For example the N8 nozzle at 30 PSI (2.0 Bar) delivers 1.90 GPM at 2.2 m radius. At 50 PSI (3.5 Bar) the same nozzle delivers 3.06 GPM (1.6x higher) at 2.6 m radius (1.18x longer).

The pressure-radius scaling law applies to the standard pop-up spray body. The radius scaling factor is 1.18 for the 30 to 50 PSI pressure range. The GPM scaling factor is 1.6 for the 30 to 50 PSI pressure range. The Rain Ling engineering team uses the pressure-radius scaling law to provide the calibrated flow data at 5 pressure points.

The pressure-radius scaling law also applies to the precipitation rate. The precipitation rate scales linearly with the GPM and inversely with the square of the radius. For example the N8 nozzle at 30 PSI (2.0 Bar) delivers 1.0 inches per hour precipitation rate at the 90-degree arc with the head-to-head spacing of 7.2 ft. At 50 PSI (3.5 Bar) the same nozzle delivers 1.6 inches per hour precipitation rate at the same head-to-head spacing. The precipitation rate is the critical engineering parameter for the landscape irrigation design.

The pressure-radius scaling law is the foundation of the Rain Ling flow rate chart reading. The Rain Ling engineering team uses the calibrated flow data at 5 pressure points to verify the pressure-radius scaling law with the R-squared correlation of greater than 0.99. The high correlation coefficient confirms the accuracy of the Rain Ling flow rate chart for the contractor reference.

4. GPM Unit Conversion (m3/h to GPM)

The GPM unit conversion from m3/h to GPM uses the formula 1 m3/h = 4.403 GPM. For example the N8 nozzle at 30 PSI (2.0 Bar) and 360-degree arc delivers 0.43 m3/h which equals 1.89 GPM. The Rain Ling flow test report provides both m3/h and GPM data for the international contractor reference.

The GPM unit conversion is the standard practice for the international contractor. The North American contractor uses the GPM unit and the European and Asian contractor uses the m3/h unit. The Rain Ling engineering team provides the calibrated flow data in both units for the international contractor reference.

The GPM unit conversion is also the foundation of the zone total GPM calculation. The contractor sums the per-head GPM from the flow rate chart to determine the zone total GPM. The zone total GPM must not exceed the available water budget from the water meter or the pump. The Rain Ling engineering team provides the zone total GPM calculator for the contractor reference.

The GPM unit conversion accuracy is critical for the contractor project bidding. The per-head GPM error of 0.1 GPM across the 8-head zone equals the 0.8 GPM zone total GPM error which can exceed the available water budget if the budget is tight. The Rain Ling engineering team provides the calibrated per-head GPM data with the +/-2 percent accuracy for the contractor project bidding.

5. Pressure Unit Conversion (Bar to PSI)

The pressure unit conversion from Bar to PSI uses the formula 1 Bar = 14.5 PSI. For example the 2.0 Bar design pressure equals 29 PSI. The Rain Ling flow test report provides both Bar and PSI data for the international contractor reference.

The pressure unit conversion is the standard practice for the international contractor. The North American contractor uses the PSI unit and the European and Asian contractor uses the Bar unit. The Rain Ling engineering team provides the calibrated flow data in both units for the international contractor reference.

The pressure unit conversion is also the foundation of the design pressure selection. The typical design pressure for the pop-up spray body is 30 PSI (2.0 Bar). The higher design pressure (40-50 PSI / 2.7-3.5 Bar) is suitable for the rotor sprinkler and the commercial application. The lower design pressure (20-25 PSI / 1.4-1.7 Bar) is suitable for the drip irrigation and the low-pressure application. The Rain Ling engineering team provides the design pressure selection guide for the contractor reference.

6. Radius Unit Conversion (m to ft)

The radius unit conversion from m to ft uses the formula 1 m = 3.28 ft. For example the 2.2 m radius equals 7.2 ft. The Rain Ling flow test report provides both m and ft data for the international contractor reference.

The radius unit conversion is the standard practice for the international contractor. The North American contractor uses the ft unit and the European and Asian contractor uses the m unit. The Rain Ling engineering team provides the calibrated flow data in both units for the international contractor reference.

The radius unit conversion is also the foundation of the head-to-head spacing design. The head-to-head spacing is the same as the nozzle radius to ensure the uniform precipitation rate. For example the N8 nozzle at the 2.2 m radius requires the 2.2 m head-to-head spacing. The Rain Ling engineering team provides the head-to-head spacing reference for the N6 to N17 nozzle family.

The radius unit conversion is also the foundation of the spray pattern design. The spray pattern is determined by the nozzle radius and the arc angle. The full circle arc covers the 360-degree area at the nozzle radius. The half circle arc covers the 180-degree area at the nozzle radius. The quarter circle arc covers the 90-degree area at the nozzle radius. The Rain Ling engineering team provides the spray pattern reference for the N6 to N17 nozzle family.

7. 4-Arc Reading Pattern for the Nozzle Matrix

The 4-arc reading pattern for the nozzle matrix is the procedure for reading the per-head GPM at each arc angle. The pattern is to select the nozzle radius (N6 to N17) for the row and the arc angle (90/180/270/360 degrees) for the column. Each cell shows the GPM at the design pressure. The matrix also shows the radius (m and ft) for the head-to-head spacing reference.

The 360-degree arc is 4x the flow of the 90-degree arc on the same nozzle at the same pressure. The radius also increases slightly with the larger arc due to the wider spray pattern. The Rain Ling engineering team provides the 6x5x4 matrix with 6 nozzle radius options 5 pressure points and 4 arc angles for the contractor reference.

The 4-arc reading pattern is the foundation of the flow rate chart reading. The contractor first selects the nozzle radius (N6 to N17) per the head-to-head spacing requirement. Then the contractor selects the arc angle (90/180/270/360 degrees) per the landscape geometry. The contractor reads the GPM at the design pressure from the cell. The contractor can also calculate the precipitation rate from the GPM and the head-to-head spacing.

The 4-arc reading pattern is also the foundation of the zone layout design. The contractor uses the mixed-arc layout with the multiple nozzle types and arc angles to match the landscape geometry. The mixed-arc layout minimizes the overspray and maximizes the uniform precipitation rate. The Rain Ling engineering team provides the sample layout drawing for the contractor reference.

8. Rain Ling Spray Nozzle Product Line and 10-Step BOFU Chart Reading Checklist

The Rain Ling spray nozzle product line supports the calibrated flow rate chart reading with the 5 SKU options. The Rain Ling adjustable spray nozzle product line is the standard option for the residential and commercial landscape irrigation. The Rain Ling engineering team can provide the specification sheets for the contractor project.

The Rain Ling spray nozzle product line includes the adjustable full-circle bubbler for the tree root irrigation the brass spray nozzles for the high-pressure application the strip spray nozzles for the narrow strip irrigation and the adjustable spray nozzles for the general landscape irrigation. Each nozzle type has the calibrated flow rate chart and the pressure-radius scaling law verification for the contractor reference.

10-Step BOFU Nozzle Flow Rate Chart Reading Checklist

1. Identify the nozzle radius (N6 to N17) from the product packaging or the catalog.
2. Identify the design pressure (typically 30 PSI / 2.0 Bar) from the irrigation system design.
3. Identify the arc angle (90/180/270/360 degrees) from the landscape geometry.
4. Read the GPM at the design pressure from the flow rate chart cell.
5. Convert the GPM to the contractor unit (m3/h or GPM) per the regional preference.
6. Verify the radius at the design pressure matches the head-to-head spacing.
7. Calculate the zone total GPM by multiplying the per-head GPM by the head count.
8. Compare the zone total GPM to the available water budget.
9. Document the nozzle selection with the per-head GPM and the arc angle for the as-built record.
10. Verify the field performance by measuring the actual GPM and the radius at the first head start-up.

For contractor project bidders ready to specify Rain Ling spray nozzles for the calibrated flow rate chart reading the Rain Ling contractor team can provide the calibrated per-head GPM data the pressure-radius scaling law verification and the field performance validation report. The Rain Ling quality system has supported the spray nozzle product line since the company founding with documented approval from major landscape contractors. For more information on the nozzle flow rate chart reading and to request a sample shipment contact the Rain Ling engineering team directly.

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