Hydraulic Motor Calculations

GPM of Flow Needed for Fluid Motor Speed

Motor Displacement (in³ per rev)   Motor RPM        GPM Flow Required

Example: How many GPM are needed to drive a 3.75 cubic inch motor at, 1500 rpm?

Formula: Motor Displacement x Motor RPM ÷ 231 = gpm

Fluid Motor Speed from GPM Input

Gallons per Minute (GPM)        Fluid Motor Displacement (in³)      RPM

Example: How fast will a 0.75 cubic inch motor turn with 6 gpm input?

Formula: 231 x GPM ÷ Fluid Motor Displacement = RPM

Fluid Motor Torque from Pressure and Displacement

Pressure (PSI)    Motor Displacement (in³)      Torque

Example: How much torque does a 2.5 cubic inch motor develop at, 2,000 psi?

Formula: PSI x Motor Displacement ÷ (2 x π) = torque in inch pounds

Fluid Motor Torque from Horsepower and RPM

Horsepower      Motor RPM      Torque

Example: How much torque is developed by a motor at 12 horsepower and 1750 rpm?

Formula: Horsepower x 63025 ÷ RPM = torque in inch pounds

Fluid Motor Torque from GPM, PSI and RPM

Gallons per Minute (GPM)  Motor PSI     Motor RPM    Torque

      =

Example: How much torque does a motor develop at 1,200 psi, 1500 rpm, with 10 gpm input?

Formula: GPM x PSI x 36.77 ÷ RPM = torque in inch pounds