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Flow Monitoring Equations And Conversions

Most systems are engineered to operate at fluid velocities lower than 15 feet/second or 4.5

meters/second. This fact, along with the following set of equations, can assist with the correct

selection of a flow monitor's measuring range. Also, keep in mind that the most accurate part of a

Lake flow meter's measuring range is within the center third of the full range. (i.e. If the nominalflow rate in a system is 10 GPM, do not purchase a flow monitor that has a full-scale flow rate of

10 GPM order the next higher full scale range.)

Known: Pipe I.D. (inches), Fluid Velocity (feet/second)Unknowns: Liquid Flow Rate (GPM)Flow Rate (GPM) = 2.447994 x (pipe I.D.) 2 x Fluid Velocity

Known: Pipe I.D. (mm), Fluid Velocity (meters/second)Unknowns: Liquid Flow Rate (LPM)

Flow Rate (LPM) = 0.0471189 x (pipe I.D.)2

x Fluid Velocity

Known: Liquid Flow Rate (GPM), Pipe I.D. (inches)Unknowns: Fluid Velocity (feet/second)Fluid Velocity (ft./sec.) = (0.408498 x Flow Rate/(pipe I.D.) 2

Known: Liquid Flow Rate (LPM), Pipe I.D. (mm)Unknowns: Fluid Velocity (meter/second)Fluid Velocity (m./sec.) = (21.22291 x Flow Rate/(Pipe I.D.) 2

Known: Pressure (PSIG), Flow Rate (GPM)

Unknowns: Hydraulic Horsepower DevelopmentHydraulic Horse Power = (Pressure x Flow Rate)/1714

Known: RPM, Pump Displacement (CubicInches/Revolution)Unknowns: Flow Rate (GPM)Flow Rate (GPM) = (RPM x Pump Displacement)/231

Flow Rate Related Formulas

Volume and Capacity Equivalents

Units CubicInches

CubicFeet

CubicMeters

Liters U.S.Gallons

ImperialGallons

Cubic Inches 1 0.0005787 0.00001638 0.016384 0.004329 0.003607

Cubic Feet 1728 1 0.028317 28.317 7.48052 6.23210

Cubic Meters 61,023.4 35.3145 1 1000 264.17 220.083

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Liters 61.0234 0.0353145 0.001 1 0.264170 0.220083

U.S. Gallons 231 0.133681 0.003875 3.78543 1 0.833111

ImperialGallons

277.274 0.160459 0.0045437 4.54374 1.20032 1

Pounds of Water

27.6798 0.016018 0.00045359 0.453592 0.119825 0.099828

Example of How To Use This Chart:Question: Determine the number of U.S. Gallons in a cubic meter.Answer: Using the column labeled U.S. Gallons and the row labeled Cubic meters, the

conversion is 264.2 gallons/cubic meter

Pressure and Head Equivalents

Units psi Ft of Water Atmospheres kg/Cm 2 Bar kPa

psi 1 2.3039 0.06805 0.07031 0.06895 6.89465

Feet of Water 0.4331 1 0.02947 0.03045 0.029926 2.99267

Atmospheres 14.696 33.931 1 1.0332 1.01319 101.319

kg/Cm 2 14.2234 32.840 0.96784 1 0.98062 98.062

Bar 14.5038 33.4153 0.9869 1.01976 1 100

kPa 0.14504 0.33415 0.00987 0.010198 0.01 1

Example of How To Use This Chart:Question: Determine the psi equivalent to 10 bar of pressure.Answer: Using the column labeled psi and the row labeled bar, the conversion factor is

14.5038 psi/bar. The equivalent pressure to 10 bar would equal 10 x 14.5038 =145.033 psi