Hydraulic Motors Calculations Guide:
GPM of Flow Needed for Fluid Motor Speed:
Motor Displacement x Motor RPM ÷ 231
Example: How many GPM are needed to drive a 3.75 cubic inch motor at 1500 rpm
Motor Displacement = 3.75 cubic inches per revolution
Motor RPM = 1500
Motor Displacement x Motor RPM ÷ 231 = 3.75 x 1500 ÷ 231 = 24.35 gpm
Fluid Motor Speed from GPM Input:
231 x GPM ÷ Fluid Motor Displacement
Example: How fast will a 0.75 cubic inch motor turn with 6 gpm input?
GPM = 6
Motor Displacement = 0.75 cubic inches per revolution
231 x GPM ÷ Fluid Motor Displacement = 231 x 6 ÷ 0.75 = 1,848 rpm
Fluid Motor Torque from Pressure and Displacement:
PSI x Motor Displacement ÷ (2 x π)
Example: How much torque does a 2.5 cubic inch motor develop at 2,000 psi?
Pressure = 2,000 psi
Motor Displacement = 2.5 cubic inches per revolution
PSI x Motor Displacement ÷ (2 x π) = 2,000 x 2.5 ÷ 6.28 = 796.19 inch pounds
Fluid Motor Torque from Horsepower and RPM:
Horsepower x 63025 ÷ RPM
Example: How much torque is developed by a motor at 12 horsepower and 1750 rpm?
Horsepower = 12
RPM = 1750
Horsepower x 63025 ÷ RPM = 12 x 63025 ÷ 1750 = 432.17 inch pound
Fluid Motor Torque from GPM, PSI and RPM:
GPM x PSI x 36.77 ÷ RPM
Example: How much torque does a motor develop at 1,200 psi, 1500 rpm, with 10 gpm
input?GPM = 10
PSI = 1,500
RPM = 1200
GPM x PSI x 36.7 ÷ RPM = 10 x 1,500 x 36.7 ÷ 1200 = 458.75 inch pounds second
Unit Conversion Guide:
| To Convert | Into | Multiply By |
|---|---|---|
| Bar | PSI | 14.5 |
| cc | Cu. In. | 0.06102 |
| °C | °F | (°C x 1.8) + 3 |
| Kg | lbs. | 2.205 |
| KW | HP | 1.341 |
| Liters | Gallons | 0.2642 |
| mm | Inches | 0.03937 |
| Nm | lb.-ft | 0.7375 |
| Cu. In. | cc | 16.39 |
| °F | °C | (°F – 32) ÷ 1 |
| Gallons | Liters | 3.785 |
| HP | KW | 0.7457 |
| Inch | mm | 25.4 |
| lbs. | Kg | 0.4535 |
| lb.-ft. | Nm | 1.356 |
| PSI | Bar | 0.06896 |
| In. of HG | PSI | 0.4912 |
| In. of H20 | PSI | 0.03613 |